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Article 230, Services

Posted By Randy Hunter, Thursday, November 01, 2012
Updated: Tuesday, December 11, 2012

Article 230 is in some ways the genesis of the electrical system, meaning that it is very often the starting point of the electrical installation for a facility. Therefore, this is where I would usually commence my inspection process. As a rule of thumb, if the service is installed in a good workmanlike manner, the rest of the installation would also look good. However, if the service is a mess, you can generally assume that you are in for a long inspection and several items to note on your inspection record. The service is the location where we have some very specific things that have to happen to insure a good reliable system for the rest of the installation. The scope of this article covers the service conductors and equipment for control and protection of services and their installation requirements.

If we do a little review, the first item to remember is the term service point. Generally, it will be very close to the location of the service; and for most residential installations which are fed underground, the service point is at the meter base (see photo 1). From the service point, we start what we call the "service” which may consist of underground or overheard conductors, and then we will actually reach what most refer to as the service, or the main disconnect. If you will look at the first page of Article 230, you will find one of those handy road maps for the NEC. This diagram is a quick reference as to where you will find the requirements for a service installation.

Photo 1. This photo shows the service point, which is at the conductor terminations below the meter.

 

Photo 1. This photo shows the service point, which is at the conductor terminations below the meter.

 

In 230.2 we find the limitation on the number of services for a building or structure; one service is usually all that is required. However, we may have special conditions which would qualify for an additional service. These are commonly at larger locations which will have fire pumps, emergency systems fed from generators, and now with the sudden rise in alternative energy, we may find other types of services (see photo 3). In 230.2(B), Special Occupancies, we have language which allows multiple services for larger facilities. Often on larger apartment complexes, you may find more than one service. This is commonly true if the serving utility supplies a single-phase service which can be limited in capacity. For example, we are limited to only 600 amps for this type of service by the utility in my area. We’ve even had large custom homes which had more than one service due to this limitation. This condition is covered in (C), and again you should be getting used to the fact that one set of rules doesn’t fit every condition, so we add the last sentence to (C) which is "by special permission.” This means that the AHJ can grant permission depending on justification which he sees fit to accept. An example of this would be some of the newer data centers being constructed where reliability is of the upmost importance, requiring redundancy within the system.

Continuing with 230.2 in (D), Different Characteristics, you will find that if you have the need for different voltages you may be allowed to have an additional service. This is common in a manufacturing facility where the office may be supplied for a 120/208-volt, 3-phase service; however, the plant has larger equipment which is more efficiently run on a 277/480-volt, 3-phase system. The last part of 230.2 is the Identification requirement, which states that if a location has more than one service or a combination of sources, then we will have to properly inform people of the other locations of power feeding that location. This is accomplished by the use of a permanent plaque or directory installed at each service notifying one of all the other service, feeders and branch circuits supplying the building or structure. As I mentioned in the last article, this is the same requirement as found in 225.37. This is more than just a convenience for the electrician, it is also for our first responders who in the event of an emergency need to disconnect all power sources to a facility and to do so in a fast, orderly fashion.

Photo 2. Here is an example of a large service with signage to identify the main. As a local amendment, Las Vegas codes require the main to have a yellow sign, which helps the first responders identify the mains service disconnects.

Photo 2. Here is an example of a large service with signage to identify the main. As a local amendment, Las Vegas codes require the main to have a yellow sign, which helps the first responders identify the mains service disconnects.

Briefly I will mention 230.3, which states that service conductors may not pass through the interior of another building. This leads us right into 230.6 which outlines what is considered to be outside of a building. Here you will find that if conductors are beneath a building under 2″ of concrete or buried 18″ down, or if you have a raceway totally encased in 2″ of concrete within a building, these conditions would be considered outside. In the 2011 edition of the NEC, we now have a new addition to this section, which is that a service riser conduit may pass through an eave when installed on the outside of a building. This is one of those areas I had never considered as inside a building for the short distance that the riser may pass through an eave; however, I guess technically it was.

The next two sections mention that no other conductors shall be contained within a raceway or cable with service conductors, with only two exceptions (which I will trust you to review, as these conditions don’t happen often). However, the requirement for raceway seals in 230.8 is one of the most overlooked and missed inspection items I’ve seen, even though it can have catastrophic results if not followed. Simply put, if you have raceways entering from underground you are to seal them, even spare empty conduits. There are several products on the market which are great for this, even duct seal putty or clay will do the job just fine. One of the reasons for this requirement is that if you have some condition which will cause overheating of the underground conductors and they are installed in PVC conduit, the conduit might exceed its allowable temperature and start to degrade and even off-gas. These gases could be and often are very flammable; so if there is any type of an ignition source, like a loose connection or an arc from a breaker actuation, it may cause these gasses to explode. This makes for great photos, however, it is very expensive to repair and the lost time for this type of failure is huge. The simple task of sealing these with an approved method limits this type of condition and could save thousands of dollars.

We will now cover several items which were mentioned briefly in my previous article. I stated in the last edition that there is a huge overlap between Articles 225 and 230 when it comes to clearances, so this will be a bit of review. However, don’t discount the importance of these requirements, as they are all related to safe installations. So open the code book and please review the actual language as I summarize these again. First in 230.9 and 230.10, we find that we need to keep conductors 3 ft. from any openings, which will include windows, doors, porches, balconies, ladders, stairs, fire escapes or similar locations.

Photo 3. Here is an example of multiple services to one building, the normal power on the right and the alternate energy service on the left.

Photo 3. Here is an example of multiple services to one building, the normal power on the right and the alternate energy service on the left.

Overhead service conductors shall not be installed beneath any openings through which materials may be moved — which would include farm or other locations which may load and unload at an elevated portal — nor shall they block any building openings. And again vegetation shall not be used as a supporting means. Which brings to mind a situation, if you have a lodge pole pine tree that has died, is this still considered vegetation or is it now considered a utility pole? Where is the AHJ when you need him?

In Part II of 230 we get into specifics for overhead service conductors. First, these conductors are to be insulated, with one exception: the grounded conductor may not need to be insulated if it is part of a cable assembly. Next, we find the size and rating requirements. Generally, the conductors are to be sized to carry the calculated load as covered in Article 220; however, we do have a minimum size requirement in 230.23(B) which is 8 AWG copper or 6 AWG aluminum conductors. In 230.24 (A) and (B), we get into the specific clearances for overhead conductors which state they shall not be readily accessible, and it then expands further to explain what makes them meet this requirement. First, they shall have an 8-ft clearance over roofs, with five exceptions. Please read and review these on your own.

Next, we get the clearances from final grade. If the service voltage doesn’t exceed 150 volts to ground and the area is only accessible to pedestrians, then we only need a 10-ft clearance. This would commonly be a backyard. Next we cover residential property and driveways, and those commercial areas not subject to truck traffic, where the voltage doesn’t exceed 300 volts to ground. Here we need 12 feet of clearance, unless the voltage exceeds the 300-volt threshold, then the distance moves up to 15 feet.

Now for the last clearance: public streets, roads, and parking areas. Here we must have an 18-ft clearance. This is very important, as I’ve seen services pulled off walls by tall vehicles as a result of overhead conductors not meeting this requirement. This can obviously be a very dangerous condition. Also, please keep in mind that at certain times of the year we may have additional cable sag, which isn’t covered in the code specifically, but should be a design consideration.

One of the most important items to remember when in this area for those doing residential inspections is the additional clearance needed when dealing with swimming pools. This has to be mentioned here and you should take a moment to go to Article 680.8 and make sure you are aware of these distances, so that if you see a pool the little bell goes off in your head that you should double check all those clearance requirements specifically related to pools. Also note that in the 2011 NEC, we have new language to consider in 230.24(E) which mentions the clearance requirements from communication wires and cables.

Articles 230.26 through 230.28 deal with the attachment and support of overhead service conductors. The point of attachment shall never be lower than 10 feet, they shall be attached using fittings identified for the use with service conductors, and if the service mast is used as the support of the final span of the service conductors, it shall be of adequate strength. I mentioned in the last issue what I considered adequate. All this language boils down to this type of an installation, where the conductors are secured by a wedge clamp device that grips the bare grounded conductor which also has the steel core strand for strength, and then the conductors enter the raceway system through a weatherhead fitting.

Next we need to jump briefly to underground service conductors. These are generally utility-owned up to the meter, but you may have different local conditions. Underground service conductors are required to be insulated for the applied voltage, again with a few exceptions, which I will leave for you to review. The size and rating of these conductors don’t vary much from the overhead conditions. Where we have a different situation, in 230.32, Protection Against Damage, please note that the main reference here is to 300.5, where you will find a fair amount of installation requirements, do and don’ts, which we will cover when we reach that portion of the code. And the last item for underground service conductors is 230.33, which deals with splices. In rare cases, we may have to do splices, and this will refer you to the proper code requirements which may fit your application.

Photo 4. As an AHJ we are called out for all kinds of things. Here we had to investigate why a customer still had power even though he had no meter. However, getting past that issue, this photo is a good example of a weatherhead fitting for the proper conductor entrance to the raceway system, including a wedge clamp device which secures the conductors to the riser conduit.

Photo 4. As an AHJ we are called out for all kinds of things. Here we had to investigate why a customer still had power even though he had no meter. However, getting past that issue, this photo is a good example of a weatherhead fitting for the proper conductor entrance to the raceway system, including a wedge clamp device which secures the conductors to the riser conduit.

We now move on to Section IV of Article 230, which is titled Service-Entrance Conductors, so this would appear to cover both the underground and the overhead applications. Section 230.40 states that each service drop, overhead service conductors, underground service conductors or service lateral shall only serve one set of service-entrance conductors. A little review here: remember the difference between overhead and underground service conductors and the overhead drop and the service lateral is dependent on who owns that portion of the system. The ironic part of 230.40 is that we follow it up with nearly half a page of exceptions to this simple one sentence requirement. One of these exceptions will allow multiple service-entrance conductors if we have multiple occupancies. From my experience, when you have a condition which isn’t simply a one-on-one situation, I would recommend reviewing this section of the code carefully to see which condition best matches what you are seeing in the field and work from there.

Moving on, I want to jump up to 230.44. I mention this only to introduce you to the fact that a cable tray installation is permitted for service-entrance conductors.

Let’s move on to more of the mechanics of service installations. In 230.54, we actually begin with the requirements for service heads where the conductors enter a raceway system. Here we cover some simple but very essential items related to how to make sure we have a good weatherproof installation and points of attachment, so we do everything possible to prevent moisture infiltration into our equipment (see photo 4). This would include a drip loop, which is one of the most basic items which I see being done poorly. The intent of a drip loop is to provide a path for water that comes in contact with the wire to drip off of a low point without directing the water into the raceway or into the connections.

So we have danced all around services, but the most basic item in a service we haven’t touched yet, and we finally get to it in Section V, Service Equipment – Disconnecting Means. Now comes the basic items that we typically train combination inspectors to concentrate on when doing service inspections, many of which are service change-outs or upgrades (see photos 5 and 6). The first item is that a means shall be provided to disconnect all conductors in a building or structure from the service-entrance conductors. In 230.70(A) we explore locations for these disconnects. The main rule is that they shall be in a readily accessible location, followed by an item stating that they shall not be in a bathroom. This leads to a little humor as bathrooms are a location I would not consider to be always readily accessible anyway. However, as we’ve said before, much of the code is written due to various interpretations which have caused the need for clarification. The next obvious but frequently missed item is that all service disconnecting means must be suitable for the prevailing conditions; this may require a certain rating of the equipment, or protection.

We continue into 230.71, where we are given the maximum number of disconnects for each set of service-entrance conductors. You will notice that I stated this in a particular way, as I’ve had enforcement issues before where we have tried to state that you are only allowed a maximum of six switches per building for disconnecting means; however, the code doesn’t exactly state that. If you have multiple sets of service-entrance conductors, you can have up to six for each set. Also we have a list of additional items which may be in your service equipment but are not included in this requirement, such as power monitoring equipment, surge-protective devices and a couple of other items.

Grouping of the Disconnects, 230.72, covers the requirement to have disconnects grouped. One of the most important items is that each disconnect shall be marked to indicate the load served: this is a must (see photo 2). The allowance for additional disconnects for such things as fire pumps, emergency systems and such are allowed above the six disconnect rule, but the code wants these separated from the others. The exact words are that these shall be "remote” from the others, so this is an AHJ call as to what is "remote.” One of the other issues that I’ve seen in multi-occupancy businesses is the fact that each occupant shall have access to the service disconnection means. This can be a real issue when the electrical rooms are often locked and the owners don’t like to give every tenant keys to the room. One reason for restricted access is to prevent tenants from storing stuff in the electrical room. Remember, we must maintain proper working clearances, and storage and electrical rooms don’t go together. One of the worst I discovered was a shopping center that decided they needed a security staff. Of course, they had to have an office to work out of, so they made the electrical room into a security office, complete with desks, chairs, microwave, lockers and more.

Electrical rooms that have service disconnects in them have to be maintained and have to allow easy access so that in the event of something getting out of hand, or the need arises to shut down a unit, it can be done without delay or creating a hazardous condition.

Photo 5 and 6. These photos show why we are writing these articles, because as combination inspectors we are running onto these types of code violation installations daily.

Photo 5 and 6. These photos show why we are writing these articles, because as combination inspectors we are running onto these types of code violation installations daily.

This leads to another issue we need to mention here; often these electrical rooms may be very large and the location of the multiple main disconnects may not always be obvious. It could even be on the backside of the equipment you see when you first enter the room. In these cases, we need to provide some form of information as to where each disconnect is. Remember, we could be dealing with first responders who are not familiar with all forms of electrical equipment, so proper signage and whatever else can be done to direct them to each main disconnect will be helpful.

Locally, one option was to paint yellow lines on the floor to guide firefighters to each switch location. We have to keep in mind that personnel may face conditions that are not optimal, such as impaired visibility due to smoke, so the markings on the floor may give us the most advantageous condition. Along with this thought, 230.77 states that it shall be plainly indicated if the switch is in the open (off) or closed (on) position.

Moving along, we have to review the rating of disconnects. Here we find some minimum sizes for certain types of services. First, it must be sized according to the load calculated back in Article 220. Now for some special conditions, if you have a one-circuit installation, then the minimum service shall not be smaller than 15 amps, as detailed in 230.79(A). In (B), a two-circuit service is limited to 30 amps. Moving up to a one-family dwelling in (C), the minimum is 100 amps, 3-wire. And then for the all others, there is a catchall in (D) where the smallest service shall be 60 amps.

Section VII, Service Equipment – Overcurrent Protection, starts with a very basic requirement: each ungrounded conductor shall have overcurrent protection. Further, the rating of this overcurrent device shall not exceed the rating of the conductor ampacity. However, no overcurrent device shall be installed in the grounded conductor, unless the breaker is one that simultaneously disconnects the grounded and the ungrounded conductors. The service overcurrent device shall be an integral part of the service disconnecting means or shall be located immediately adjacent thereto.

The last thing we need to review in this article is 230.95, Ground-Fault Protection of Equipment. There are a few conditions that have to be met to kick in this requirement. First, the service has to be rated 1000 amps or more, and be a solidly grounded wye service of more than 150 volts to ground but not exceeding 600 volts phase-to-phase. So what fits this? It would commonly be our 277/480 wye services. The grounded conductor shall be solidly connected to ground through a grounding electrode conductor. The other information related to this requirement covers the settings, fuses, and the performance testing requirement. Generally speaking, on the ground fault protected systems we had in our area, we required third party testing. This would insure that the devices were set at the proper settings according the installation and the design professional’s requirements. From the factory, the settings are generally set to minimums which will cause nuisance tripping if not adjusted properly. We would then get a copy of this report and submit it as part of the record for the job. This was the best way, due to the time and equipment required, for this type of testing to be conducted. One extra note here, as simple as this may sound it is always a good idea to have this done and the report in hand before you authorize it to be energized.

This concludes Article 230; once again we have only hit the high spots and provided information which is common in the field and for testing purposes. Please take the time to thoroughly review the article in detail for those areas not specifically covered here. In the next issue, we will cover Article 240, Overcurrent Protection.


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Tags:  Featured  November-December 2012 

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Appreciating Hazardous Areas

Posted By Steve Foran, Thursday, November 01, 2012
Updated: Wednesday, December 12, 2012

Photo 1. Electrical wiring in a hazardous (classified) locationIt was the turn of the century and after thirteen years working on the utility side of the transformer I took on the role of managing a Hazardous Area Electrical Training Center. Ironically, at the time I was completely unaware of hazardous areas. Hey, everyone has to learn about something for the first time.

During my first week, I took the most popular course offering. It was an introductory course and I learned about glanding, zones, divisions, IS systems, standards, work methods and many concepts about which most people, including most electrical professionals, know very little.

A half dozen electricians and technicians, all of whom were experienced in working in hazardous areas also attended the course; their presence really enriched the learning. As the course ended and comments were openly shared, I learned a big lesson.

Every single participant commented that although they had heard this was a good course they did not think that there would be much that they would learn — because they already had lots of experience. And without exception every person (including senior engineers who governed electrical inspections) said, "I had no idea there was so much I did not know about hazardous areas.”

Therein lays the universal truth. People tend to strongly believe that their knowledge, beliefs and convictions are complete and correct. This belief in our abilities is often so strong that we do not consider that we might be wrong or that maybe, just maybe, we do not have all of the information.

Truly, there is far more that you do not know than what you know. This is OK. However, it is a problem when you think you are right when you are wrong. And when it comes to hazardous area electrical work, thinking you know what you are doing when you are wrong is a major problem that could lead to a catastrophe.

I am no longer involved with the training center which has since scaled back operations for a number of reasons, the main one being that we could not get enough people to believe that there were things about hazardous areas that they did not know. Companies and individuals most frequently justified that they did not need to take the hazardous area electrical training because they already knew it. Yet participants’ feedback repeatedly mentioned that they gained knowledge and skills that they thought they already had or did not need.

There are two ideas you can use from this.

The first is very simple and specific to hazardous areas. If your work involves hazardous areas, I do not care how much you already know, commit to continually upgrade your knowledge in this field (kudos to IAEI for focusing on this important topic in this issue).

The second is concerned with your talents and applies more generally. It is very important to recognize and appreciate the skills, knowledge and abilities that you do possess. Not that these alone define you as a human being, but they make up a large part of who you are. It is also important to appreciate these aspects in the people around you. That is, if you want them to feel valued.

However, there is a balance that you must find in appreciating your talents and developing your talents (as well as those of others). Knowing your limitations and acknowledging that you do not know everything enables you to use your talents wisely and leads you to develop and improve them. When you do this, you honor and respect your talents. This is a true sign of appreciation — appreciation to yourself and to all those who have contributed to your talents.

The great thing is that when you come to truly appreciate your own talents and abilities you will settle for nothing short of excellence… guaranteed.


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Tags:  Featured  November-December 2012 

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5 Methods of Protection

Posted By IAEI, Thursday, November 01, 2012
Updated: Wednesday, December 12, 2012

All three elements of the fire triangle — oxygen, ignition source, and fuel — must be present simultaneously and in specific quantities for a fire or explosion to occur. Often, in hazardous (classified) locations, the electrical system will be the ignition source of the triangle. This article looks at five methods of protection to prevent electrical systems from becoming ignition sources in these locations.

Location of electrical equipment

This method involves designing the electrical system so that much or all of it is located outside the classified areas. An accurate area classification of the space and careful placement of the electrical equipment are required. Depending on the type of process and the facility involved, this option could eliminate some or all special electrical equipment; it would be cost effective and would result in safer installations. [NEC 500.5(A) Information Note and 505.5(A) Information Note 2].

However, this method cannot always be used since in some cases the electrical components must be installed within the operating process; for example, pumps, compressors, instrumentation.

In other cases, the electrical equipment can be located to an area less likely to contain ignitible concentrations. Relocating equipment a relatively short distance away often has a major impact on safety and equipment requirements; the relocation can also result in decreased costs.

Figures 1, 2 and 3 demonstrate this protection method by relocating the luminaires. In figure 1, the luminaires are located within Division 1. In figure 2, the luminaires have been moved to Division 2. Then in figure 3, they have been installed outside Class 1, Division 1 or 2 locations. An accurate area classification and careful placement of electrical devices will always reduce both cost and risk of ignition in Class I locations.

 Figure 1. Luminaires installed in Class I, Division 1 locations must be suitable for that location.

Figure 1. Luminaires installed in Class I, Division 1 locations must be suitable for that location.

 Figure 2. Luminaires installed in Class I, Division 2 location must be suitable for that location.

 Figure 2. Luminaires installed in Class I, Division 2 location must be suitable for that location.

Figure 3. Luminaires installed outside a Class I, Division 1 or 2 location can be suitable for general use.

 Figure 3. Luminaires installed outside a Class I, Division 1 or 2 location can be suitable for general use.


The principles are exactly the same for space classified using NEC 505, the Zone system. As in the Division system, a relatively minor relocation of many electrical devices could result in the use of ordinary location equipment. As the equipment location is moved from Zone 0 to Zone 2, the number of permitted protection techniques increases. This provides more flexibility, a decrease in cost, and a safer installation.

However, in Zone 0 spaces, Article 505 allows only electrical equipment that is protected by the intrinsic safety, or encapsulation techniques. This stipulation prohibits many electrical functions from taking place in that space.

 Figure 4. Exhaust duct with the electric fan motor installed inside the duct (hazardous location)

 Figure 4. Exhaust duct with the electric fan motor installed inside the duct (hazardous location)

 Figure 5. Exhaust duct with the electric fan motor outside the duct (hazardous location)

Figure 5. Exhaust duct with the electric fan motor outside the duct (hazardous location)

With accurate area classification, on the other hand, much of the electrical equipment — lighting, alarm devices, security devices and communication devices — can be relocated to less classified or unclassified locations in many facilities. One example involves the location of the exhaust fan motor when ventilation is provided in hazardous (classified) locations. NEC 500.5(B)(1) Information Note 2, item 5 and 505.5(B)(1) Information Note 2 identify the "interior of an exhaust duct that is used to vent ignitible concentrations of gases or vapors” as a Division 1 or Zone 0 location. Figure 4 shows the exhaust fan motor located inside the duct, which is permitted in a Division system if the fan is explosionproof. In almost all applications, the motor could be located outside the duct in a Division 2 or unclassified location as shown in figure 5, and would achieve the same purpose using an ordinary location motor. With limited protection techniques permitted in Zone 0, installing the motor outside the duct may be the only practical option.

Containment of combustible materials

Controlling fugitive emissions

While the Environmental Protection Agency regulations address release of particles into the atmosphere in a different way than area classification, any control of release will have an impact on the area classification. This is not to say Division 1, Zone 0 or Zone 1 areas do not exist, but large-scale areas are not as common as they were in the past. It is no longer environmentally acceptable to vent waste products from a process, which, in some industries, could include flammable and combustible vapors into the atmosphere.

These EPA requirements have led to greater control of fugitive emissions, defined in American Petroleum Institute (API) Recommended Practice (RP) 500, Section 3.2.24 as "continuous flammable gas and vapor releases that are relatively small compared to releases due to equipment failures. These releases occur during normal operations of closed systems from components such as pump seals, valve packing and flange gaskets.”

Photo 1. Tight fill combustible liquid transfer

Photo 1. Tight fill combustible liquid transfer

NFPA 30, Flammable and Combustible Liquids Code defines fugitive emissions as both continuous and intermittent releases and includes additional components that may be the source of release. Today vapor recovery is provided with many fill operations involving flammable or combustible liquids. Consequently, a much smaller volume of flammable or combustible vapor is released into the atmosphere. A common example of vapor recovery is used with gasoline delivery (see photo 1). As the gasoline tanks are filled, the vapors located above the liquid level in the tank are recovered into the tanker trucks, rather than being forced out the tank vents. These recovered vapors are then taken back to the bulk storage facilities, where vapor recovery is also provided (see photo 2).

Photo 2. Vapor recovery operation at the bulk storage facility

Photo 2. Vapor recovery operation at the bulk storage facility

Adoption and enforcement of EPA regulations could have a different impact on area classifications from state to state, region to region and even from industry to industry since the goal of those regulations is environmental not prevention of ignitible concentrations as it relates to electrical installations. The National Electrical Code is used both in the U.S. and in other countries, some of which may have different regulations and may not have any environmental regulations.

Controlling the fuel side of the fire triangle

For Class II and Class III locations, dust collection systems and housekeeping have a major affect on area classification through the containment of combustible or ignitible material. These concepts provide health benefits to employees, greater mechanical life for moving equipment, and minimize overheating of electrical equipment that would otherwise be covered with layers of dust or fibers.

In order to realize the benefit of dust collection and housekeeping and also to use this method of protection by controlling the fuel side of the fire triangle, the installation must comply with the standards and recommended practices for the specific industry (see sidebar).

Section 3-3.2 of NFPA 499 indicates that areas designated as unclassified based on dust collection should be required to include adequate safeguards and warnings against failure. This might include some method to turn dust-producing equipment off when dust collection equipment is inoperable. Photo 3 shows a dust collection system that limits the dust cloud in this operation and, in turn, minimizes the dust layering. That in combination with housekeeping can greatly limit the amount of special electrical equipment needed for this operation.

 Photo 3. Typical dust collection system (equipment shown inside of structure)

Photo 3. Typical dust collection system (equipment shown inside of structure)

In many facilities, classified areas can be limited by providing closed storage vessels and transporting flammable and combustible materials through well-maintained closed piping systems. NFPA 497 and 499 both recognize these situations as unclassified areas. Special electrical equipment in the closed systems might be limited to instrumentation devices.

Containing with solid partitions

Separating hazardous locations with walls, enclosed vaults, or other solid partitions is another means to contain combustible materials and limit area classification. Containing the flammable or combustible materials is possible with Class I, Class II and Class III location materials. Since dusts and fibers/flyings are solid materials rather than gas, they may be easier to contain by separation. Where separation of smaller hazardous areas within a larger facility is used as a method of protection, extreme caution should be used to completely close off the classified spaces. All openings and penetrations through the separation must be considered for possible releases of the combustible materials. Figure 6 shows an example where an unpierced wall on one side of a structure that contains a Class I point of release ends the classified space. The opposite wall of the structure has openings that require the classified area to extend outside the structure.

Figure 7 shows a structure containing a Class II point of release. Walls on two sides of a structure are unpierced and an additional wall has an infrequently used self-closing door. The classified space does not extend beyond any of these walls. The other wall of the structure has a frequently opened door that requires the classified area to extend outside the structure.

 Figure 6.  Extent of classified locations can be extended due to openings in walls or structures

 Figure 6.  Extent of classified locations can be extended due to openings in walls or structures

 Figure 7.  The classified space does not extend beyond the walls

Figure 7.  The classified space does not extend beyond the walls

Ventilation

NEC 500.5 recognizes the affect of ventilation in the area classification process. Adequate ventilation is defined in Section 1-3 of NFPA 497 as "a ventilation rate that affords either 6 air changes per hour, or 1 cubic feet per minute (cfm) per square foot of floor area, or other similar criteria that prevent the accumulation of significant quantities of vapor-air concentrations from exceeding 25 percent of the lower flammable limit.”

It should be recognized that the air change information included in this definition is not very specific. If the air changes noted do not limit the concentration of vapors to 25 percent of the lower flammable limit, the area classification should not be adjusted. In many cases where limited releases are occurring, those air change rates will likely provide adequate ventilation. In other cases where larger releases are expected, it may be determined that those air change rates are not sufficient to change the area classification. A review of the specific occupancy code, standard or recommended practice is advised prior to adjusting the area classification based on 6 air changes per hour. Some standards are very specific about the location of the exhaust and supply ducts, depending on the vapor density of the material involved. Some require product shutdown upon failure of ventilation. Others require gas detection systems to be interconnected with shutdown of a process. In every case, the code, standard or recommended practice for the facility should be considered prior to adjusting area classification based on ventilation.

Section 3-3.2 of NFPA 497 also indicates that outside installations and installations within open or partially open structures may be considered to have adequate ventilation and be classed "unclassified.” Nevertheless, a review of many of the occupancy documents will result in those spaces being classified. Section 1-2.3 of NFPA 497 indicates the occupancy document is a recommended practice and is intended as a guide that should be applied with sound engineering judgment. For example, when the information is used within its context and all of the parameters are considered, some outside installations will result in unclassified areas and others will result in classified areas. When it is determined that adequate ventilation has been provided, the specific standard for the industry or material involved will provide the guideline for the impact of ventilation on the area classification.

Great care should be used when the classification of a space and type of electrical equipment is changed based on the fact that ventilation is provided. Ventilation is required and may be provided in many facilities for reasons other than reducing the area classification. NFPA 500, Section 38.7 addresses attic ventilation; Section 54.4 requires ventilation of elevator rooms to maintain required temperatures during fire fighter service operations; Chapter 49 requires all rooms and occupied spaces in buildings to be ventilated; Section 49.2.2.1 requires various types of occupancies to conform to ASHRAE 62, Ventilation for Acceptable Air Quality. ASHRAE Standards provide ventilation requirements for spaces intended for human occupancy and specify minimum and recommended ventilation air quantities for preservation of the occupant’s health, safety and well-being.

NFPA 91, Standard for Exhaust Systems for Air Conveying of Vapors, Gases, Mists and Noncombustible Particulate Solids provides some general requirements for design and construction of exhaust systems which may be modified by other applicable standards. Systems that comply with this standard are limited to conveying flammables that are not more than 25 percent of the lower flammable limit unless they also meet the requirements of NFPA 69, Standard on Explosion Prevention Systems. Under normal conditions, fire detection and alarm systems are not permitted to shut down these air-moving devices.

Grounding and bonding requirements

Grounding is required for the protection of electrical installations, which, in turn, protect the buildings or structures in which the electrical systems are installed. Persons and animals that may come into contact with the electrical system, or are in these buildings or structures, are also protected if the grounding system is installed and maintained properly. The National Electrical Code does not imply that grounding is the only method that can be used for the protection of electrical installations, people or animals. Insulation, isolation and guarding are also suitable alternatives under certain conditions. Grounding of specific equipment is covered in several articles of the NEC. The scope and general requirements for grounding and bonding are contained in NEC 250.4. Included are the grounding and bonding performance requirements for grounded systems and ungrounded systems.

The Code places some special requirements for grounding and bonding in hazardous (classified) locations. These requirements can be found in NEC 501.30 for Class I locations; in 502.30 for Class II locations; and in 503.30 for Class III locations. For Class I, Zone 0, 1 and 2 hazardous (classified) locations, see NEC 505.25. Since this protection method is far more detailed than can be covered in this article, it is recommended that the reader refer to these Code sections, and to chapter 2 of Hazardous Locations, and to Soares Book on Grounding and Bonding, both books published by IAEI.

System shutdown and alarms

Methods of protection for hazardous locations often include engineered designs that incorporate specific ventilation systems, interlocks, and alarms. The basic objective of these systems is to minimize or remove one or more of the components of the fire triangle. Where movement of air is applied, the possibility of ignitible concentrations of hazardous atmospheres is reduced. A couple of examples are found in NEC 511.

Section 511.3(C)(1) indicates that the area 450 mm (18 in) above the floor in a commercial garage is unclassified if there is mechanical ventilation that provides a minimum of 4 air changes per hour or 1 cubic foot per minute of exchanged air across the entire floor area, and if the exhausted air is taken from a point within 0.3 m (12 in.) of the floor.

Section 511.3(C)(3) also indicates that lubrication service facilities — consisting of pit, belowgrade work area or subfloor work area — are classified according to whether ventilation is provided. If ventilation is not provided, any pit or subfloor work area is classified as Class I, Division 1 up to the floor level. If mechanical ventilation provides a minimum of 6 air changes per hour, the classification is Class 1, Division 2. There is no transfer of any Class 1 liquids, pits or work areas below grade level that are provided with not less than 0.3 m3/minute/m2 (1 cfm/ft2) of exhaust ventilation. The exhausted air must be taken from a point within 300 mm (12 in.) of the floor level of the pit or subfloor work area. Note that there are no requirements for interlocks or alarms in these Code rules; however, the Code does require that the exhaust ventilation for the pit of belowgrade work areas be operational at all times when the building is occupied or when vehicles are parked over the pit or belowgrade work area(s). A mechanical engineer can usually provide a design and documentation verifying to approving authorities that the require air movement or exhaust has been provided to allow the area to be considered unclassified. It is important that the occupant and operators of the facility understand the importance of these ventilation systems as they relate to building and personnel safety.

Another method of protection can be provided by a combination of gas detection system and air changes, which are generally specific to the project or location. An example would be a design that might include an exhaust system that provides a minimum number of air changes in the appropriate location, depending on the properties (vapor density) of the gas involved. If the gas is heavier-than-air, exhausted air will generally be taken from locations close to the floor or grade level. If the gas is lighter-than-air, exhausted air is usually taken from locations near the highest point of the facility or location. Interlock systems are often used to provide warnings by audible and visual alarms, or both in combination, to warn qualified operators that the method or protection is not operational. In addition to interlocks for personnel warning systems, there could be a shutdown interlock system that removes power from the electrical system in the area where the exhaust or ventilation system has failed or is not operating. This can be accomplished by using shunt-trip breakers and contactors that are interlocked with the specific exhaust or ventilation system. Usually any necessary electrical circuits or systems, such as emergency lighting equipment of exit lighting are provided in these areas, but they are installed using the appropriate protection technique for the area so they remain operational.

Sometimes gas detection systems are used as the primary protection method and are part of a system design that includes not only detection of ignitible concentrations but also works cooperatively with an exhaust or ventilation system and a shunt-trip interlocking system for system shutdown. These systems are usually equipped with early warning audible and visual alarms to warn facility personnel or operators of ventilation or exhaust systems failure and ignitible mixture accumulations that are increasing to hazardous (explosive) levels. These types of engineered systems or designs are generally limited to applications in industrial facilities or to installations where there are qualified persons who are familiar with the operation and servicing of these safety systems. Even where these multilevel methods of protection are employed, safety depends on qualified persons that can respond appropriately if any necessary component of the designed system were to fail or become inoperative.

Documentation

The Code requires documentation of areas designated as hazardous (classified) locations as provided in 500.4(A). Although this section only calls for the hazardous areas to be designated, often the documentation provided by engineering and design teams includes how the area was classified, together with information about associated exhaust or ventilation systems and interlocked systems that allow for definitive delimitation of the hazardous locations. The documentation should also include the hazardous area classification that can result from ventilation system failure. As indicated in NEC 500.4(A), the documentation is required to be available to those authorized to design, install, inspect, maintain, or operate electrical equipment at those locations. It is important that an adequately designed protection system be properly operated and monitored to maintain minimum levels of safety in hazardous locations.


Dust Collecting and Housekeeping

A few of the standards and recommended practices that include specific requirements related to dust collection and housekeeping are:

  • NFPA 36.  Standard for Solvent Extraction Plants
  • NFPA 61.  Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Products Facilities
  • NFPA 120.  Standard for Coal Preparation Plants
  • NFPA 480.  Standard for the Storage, Handling, and Processing of Magnesium Solids and Powders
  • NFPA 481.  Standard for the Production, Processing, Handling, and Storage of Titanium
  • NFPA 482.  Standard for the Production, Processing, Handling, and Storage of Zirconium
  • NFPA 499.  Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas 
  • NFPA 651.  Standard for the Machining and Finishing of Aluminum and the Production and Handling of Aluminum Powder 
  • NFPA 654.  Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids
  • NFPA 655.  Standard for the Prevention of Sulfur Fires and Explosions
  • NFPA 664.  Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities


Ventilation requirements for codes & standards

NFPA 30, Flammable & Combustible Liquids Code requires all atmospheric storage tanks that contain flammable or combustible liquids to be adequately vented to prevent the development of vacuum or pressure conditions that might distort the tank or exceed the design pressure of the tank. This adequate vent of the tank is not going to provide ventilation that is adequate to prevent the accumulation of vapor-air concentrations from exceeding 25 percent of the lower flammable limit. This code includes ventilation requirements in sections 2.2.7.5 for vaults that contain tanks storing Class I liquids; 2.3.4.4 for tank buildings; 4.4.2.7 for inside liquid storage areas; 4.6.3.4 for hazardous materials storage lockers; and 5.3.4.1 for enclosed processing areas handling or using Class I, Class II or Class III liquids above their flash point. With the ventilation requirements met, some of these spaces are Class I Division or Zone 1 and others are Class I, Division or Zone 2. 

NFPA 57, Liquefied Natural Gas (LNG) Vehicular Fuel Systems Code requires buildings with indoor fueling to provide continuous mechanical ventilation or a mechanical ventilation system that is activated by a continuous gas monitoring system, which activates the ventilation system when a gas concentration of one-fifth of the lower flammable limit is present. Both of these ventilation options are required to shut down the fuel system if the ventilation system fails. The ventilation rate shall not be less than one cubic foot per minute per 12 cubic feet of room volume. When adequate ventilation is provided, some locations are classed Class I, Group D, Division or Zone 1 and others Class I, Group D, Division or Zone 2. 

Additional requirements are provided for commercial marine vessels operating on LNG.

NFPA 120, Standard for Coal Preparation Plants allows adequate ventilation to reduce area classification from Class I, Division 2 where methane can reach ignitible concentrations to unclassified. Any equipment that is needed to restore the facility to a safe condition such as lighting, ventilation, and sump pumps must be installed based on Class I, Division 1 requirements. Additional gas monitoring and shutdown provisions are also required when area classification is reduced because of ventilation.

NFPA 409, Standard on Aircraft Hangars permits mechanical ventilation for vapor removal in accordance with NFPA 91, Standard for Exhaust Systems for Air Conveying of materials.

NFPA 651, Standard for the Machining and Finishing of Aluminum and the Production and Handling of Aluminum Powders includes a reference to the ventilation requirements in NFPA 30, where aluminum dusts or powders are present in the same area with flammable or combustible solvents.

NFPA 820, Standard for Fire Protection in Wastewater Treatment and Collection Facilities indicates that ventilation rates used in that standard are based on air changes per hour and are calculated by using 100 percent outside air for the supply air that is exhausted. Air changes are calculated using the maximum aggregate volume of the space to be ventilated under normal conditions. Ventilation is not required, but is permitted if designers and owners desire area classification reduction. Ventilation systems used to reduce area classification in this standard are required to have both supply and exhaust fans, a means to provide power from an alternate power source, a power loss alarm on the primary power source, and include a variety of ventilation rates depending on what location or function in the collection and treatment process is involved and area classification that is desired to be achieved. All continuous ventilation systems installed for these facilities are required to include flow detection devices which are connected to an alarm signaling system and include both visual and audible alarms located in specific locations.

NFPA 853, Standard for Installation of Stationary Fuel Cell Power Plants requires mechanical ventilation of rooms where fuel cell power plants are located. The exhaust rate must be at least 1 cfm per square foot of floor area for the room and not less than 150 cfm of total floor area. That standard also requires the ventilation to be interlocked so that the unit will be shut down upon loss of ventilation.


Excerpted from Hazardous Locations, Second Edition, International Association of Electrical Inspectors, Richardson, Texas. Updated to NEC-2011.

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Diversify Your Investment Risk

Posted By Jesse Abercrombie, Thursday, November 01, 2012
Updated: Wednesday, December 12, 2012

All investments carry risk. But, as an investor, one of the biggest risks you face is that of not achieving your long-term goals, such as enjoying a comfortable retirement and remaining financially independent throughout your life. To help reach your objectives, you need to own a variety of investment vehicles — and each carries its own type of risk.

If you spread your investment dollars among vehicles that carry different types of risk, you may increase your chances of owning some investments that do well, even if, at the same time, you own others that aren’t. As a result, you may be able to reduce the overall level of volatility in your portfolio. (Keep in mind, though, that diversification can’t guarantee a profit or protect against all losses.)

To diversify your risk factors, you first need to recognize them. Here are some of the most common types of investment risk:

Market risk. This is the type of risk that everyone thinks about — the risk that you could lose principal if the value of your investment drops and does not recover before you sell it. All investments are subject to market risk. You can help lessen this risk by owning a wide variety of investments from different industries and even different countries.

Inflation (purchasing power) risk. If you own a fixed-rate investment, such as a Certificate of Deposit (CD), that pays an interest rate below the current rate of inflation, you are incurring purchasing power risk. Fixed-income investments can help provide reliable income streams, but you also need to consider investments with growth potential to help work toward your long-term goals.

Interest-rate risk. Bonds and other fixed-income investments are subject to interest-rate risk. If you own a bond that pays 4% interest, and newly issued bonds pay 5%, it would be difficult to sell your bond for full price. So if you wanted to sell it prior to maturity, you might have to offer it at a discount to the original price. However, if you hold your bonds to maturity, you can expect to receive return of your principal provided the bond does not default.

Default risk. Bonds, along with some more complex investments, such as options, are subject to default risk. If a company issues a bond that you’ve bought and that company runs into severe financial difficulties, or even goes bankrupt, it may default on its bonds, leaving you holding the bag. You can help protect against this risk by sticking with "investment-grade” bonds — those that receive high ratings from independent rating agencies such as Standard & Poor’s or Moody’s.

Liquidity risk. Some investments, like real estate, are harder to sell than others. Thus, real estate is considered more "illiquid” than many common investments.

Make sure you understand what type of risk is associated with every investment you own. And try to avoid "overloading” your portfolio with too many investments with the same type of risks. Doing so will not result in a totally smooth journey through the investment world, but it may help eliminate some of the "bumps” along the way.


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Introduction to PLCs

Posted By Steve Vidal, Thursday, November 01, 2012
Updated: Wednesday, December 12, 2012

The programmable logic controller (PLC) is a microprocessor-based system that accepts input data from switches and sensors, processes that data by making decisions in accordance with a stored program, and then generates output signals to devices that perform a particular function based on the application.

An important review

It is important to review previous articles that dealt with magnetic motor starters, input and output devices, and ladder logic as they provide some necessary background for PLC operation. As you recall, the magnetic motor starter is the controller that operates the connected motor load. Two-wire and three-wire control circuits use various types of input devices to energize the coil of a magnetic motor starter. These input devices are pushbuttons, proximity sensors, liquid level sensors, photoelectric sensors, selector switches, and pressure transducers. Typical output devices are contactors, magnetic motor starters, solenoids, pilot lights, and intelligent display panels. These output devices will behave according to the connection of the input devices.

It is also important to review some background on logic functions and binary number states as they relate to PLCs. The binary number system has two numbers, namely 0 and 1. The 0 refers to a logic state low (off), and the 1 refers to a logic state high (on). Ladder logic is the symbolic language of motor control.

Two logic functions most common in motor control circuits are the "and” operation and the "or” operation. The "and” operation occurs when two contact devices are connected in series. For example, if two switches are connected in series, switch #1 "and” switch #2 must both be in the on position for the load to be energized. In terms of logic, this means switch #1 (input #1) and switch #2 (input #2) can either be in the on or off position. When both switches are on (logic state 1), the load is energized. When both switches are off (logic state 0), the load is de-energized.

The "or” operation occurs when two contact devices are connected in parallel. For example, if two switches are connected in parallel, either switch #1 "or” switch #2 can be in the on position for the load to be energized. In terms of logic, this means switch #1 (input #1) and switch #2 (input #2) can either be in the on or off position. When one of the switches is on (logic state 1), the load is energized. A truth table is a graphical way of showing how inputs and outputs behave according to logic function. The "ones” and "zeros” in the table are binary numbers that represent on and off states. Figure 3 illustrates PLC logic functions.

Figure 1. A 3-wire central circuit listing input and output fuctions

Figure 1. A 3-wire central circuit listing input and output fuctions

Figure 2. Ladder diagram as entered into PLC programing

Figure 2. Ladder diagram as entered into PLC programing

Figure 3. PLC Logic functions

Figure 3. PLC Logic functions

Necessity for a programming language

A traditional motor control circuit is normally a hardwired system; therefore, any required circuit design change is a rather involved process in terms of material and labor. The manufacturing and automotive industries were interested in automating the motor control process in a way that offered flexibility to make circuit design changes easier. The interesting challenge was to design a programming language that would allow the industrial electrician a familiar way to communicate with the electronics of the PLC. This programming language would utilize symbols encountered in conventional ladder diagrams of the hardwired variety.

The original purpose of the PLC was to allow electro-mechanical and electronic input devices to communicate with a computer that would perform logical operations on the input data and output a corresponding signal to some form of output device (see figure 2).

Understanding inputs and outputs

To properly understand PLCs, it is very important to break down functions into inputs and outputs. If we revisit the standard three-wire control circuit as shown in figure 1, you will notice there are a normally closed momentary stop pushbutton and a normally open momentary start pushbutton. These contact devices represent the input function. The coil of the magnetic motor starter represents the output function. The normally open start pushbutton energizes the coil of the magnetic motor starter and the normally closed stop pushbutton de-energizes the coil of the magnetic motor starter. In this example, the PLC would recognize two input functions; the stop and start pushbuttons, and one output function the coil of the magnetic motor starter.

In very simple terms, a PLC is designed to perform three tasks: (1) check the input status, (2) execute the program, and (3) update the output status. The PLC checks the input status by scanning each input to determine if the connected device is on or off and then records that information in memory. Next, the PLC has to execute the user program one line at a time to make decisions. For example, maybe the user program tells the PLC to turn on an output device if input #1 is on, and then turn off another output device if input #2 is off. The PLC will analyze these conditions and execute the appropriate action and then store that information in memory. Lastly, the PLC has to update the output status. This means it will send data to an output device such as the coil of a magnetic motor starter to enable some type of manufacturing process to begin. The time it takes the PLC to go through this cycle is called the scan time.

The PLC uses a programming language that is based upon readily identifiable symbols common to motor control. Handheld programmers or PCs are the most common methods for programming the PLC. Figure 2 is an example of programming code setup to perform an "and” operation. Switch #1 and switch #2 are connected in series to the coil of a relay. The first rung of the ladder diagram shows two inputs; namely, switch #1 and switch #2 and an output, namely the relay. Each rung of the ladder diagram should contain input(s) and output(s). The input(s) should be the first listed instruction and the output(s), the last listed instruction. Usually programming code requires the END command to be listed as the last instruction on the last rung of the ladder diagram.

The following specifications are for a GE Fanuc PLC. This list will give you a sense of the type of information that is important in the selection and application of the PLC.

80188 CPU 8MHZ Clock Speed

Input Points – 16

Output Points – 12

High Speed Counter – 10KHZ

Maximum User program – 1K

Registers – 256 Words

Internal Coils – 2560

Memory backup w/Lithium battery – 5 years

LED Status Indicators for I/O and CPU Status

Scan Rate – 18mS/1K of Logic

The programmable logic controller gives the end user a very flexible means to automate the control circuit process in a manufacturing environment.


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LED Lighting for Hazardous Locations

Posted By Steve Henry, Thursday, November 01, 2012
Updated: Wednesday, December 12, 2012

Light-emitting diodes are not a particularly new technology. Affordable LEDs have been available since the late 1960s. From then until now, the technology has steadily progressed in terms of cost-effectiveness, color options, light output, and efficiency. Thanks to ongoing advancements in semiconductors, optics, and materials, LED applications have grown exponentially.

Because LEDs are rugged, reliable, and long-lived, they’re still the universal choice for indicator lamps on all types of electronic equipment more than 40 years after they first began to replace incandescent lamps. They soon found application in alphanumeric displays for calculators, clocks, watches, and appliances; and as brighter LEDs became available in more color options, they quickly became ubiquitous in traffic lights, animated signage, automotive brake and signal lights, decorative lighting, flashlights, and much more.

Photo 1. LED lighting is superior for safe lighting of variouss locations

Photo 1. LED lighting is superior for safe lighting of variouss locations

All of these applications benefit from the relatively low cost of LEDs, their remarkable efficiency, their minimal environmental footprint, and their long and reliable operation even under extreme conditions. But the advantages of LED technology have never been available as a realistic choice for high-quality area and task lighting. Until now.

At the Gates to the City

For industrial settings, hazardous locations, and public areas such as parking garages, LED lighting has always been something of a golden city: rumored to be just over the horizon, but never actually within reach. But in the last two years, things have changed. Through advancements in technology and manufacturing, bright white LED luminaires for industrial lighting applications are now coming to market.

Recent legislation in the U.S. has led to the phase-out of mercury vapor ballasts and lamps as well as 150 to 500 watt metal halide luminaires. Lighting designers who used to choose these products for their broader spectrum compared to high-pressure sodium, and for their longer life compared to incandescent, must now look at other options. LED enters the market at the perfect time to fill these needs, while far exceeding government mandated efficiency standards.

While other lighting sources will continue to play their roles, LED clearly owns the future.

It’s no longer just a rumor; LED is here today and promises to become an increasingly dominant technology in the future for all kinds of industrial and general purpose lighting needs.

Figure 1. Comparison of lighting designs in a walkway installation

Figure 1. Comparison of lighting designs in a walkway installation

Getting Oriented

Whenever a new technology emerges, it takes time for standards to coalesce and for new concepts to become clear. That’s true not only for end-users, but also for manufacturers who are just getting started with technologies that differ radically from what they’re used to working with.

Consider the first few months after the introduction of compact fluorescent lamps. Manufacturers had to play a guessing game regarding which wattages and sizes would become standard, and what luminaires they would need to design to accommodate these standards. Through the passage of time, standards emerged, products based on incorrect guesses and bad ideas were weeded out, and customers gained access to proven products that would provide reliable performance and compatibility for years to come.

Although practical LED industrial lighting has emerged fairly recently, the field has stabilized to a point where this technology can be regarded with practically the same understanding and confidence that compact fluorescent lighting has earned. Poorly designed products are being purged from the market, misleading claims have been retracted, and the major manufacturers are providing products that perform as advertised.

The market is still experiencing somewhat of a holdover in which misconceptions, uncertainties, and fears continue to persist. By shedding light on the most widely misunderstood issues, we hope to help you make more informed decisions today and to have a better idea of what to expect for LED lighting in the years ahead. While other lighting sources will continue to play their roles, LED clearly owns the future.

Figure 2. LEDs are directional, enabling much higher efficiency compared to a conventional lamp mounted in a luminaire. Bulb: HID lamps emit light in every direction; this light is controlled using a reflector or refractor. The result is poor utilization, with efficiencies as low as 40%. LED directs the light to where it’s needed without the use of external optics. This results in efficiencies as high as 80%.

 

Figure 2. LEDs are directional, enabling much higher efficiency compared to a conventional lamp mounted in a luminaire.
Bulb: HID lamps emit light in every direction; this light is controlled using a reflector or refractor. The result is poor utilization, with efficiencies as low as 40%.
LED directs the light to where it’s needed without the use of external optics. This results in efficiencies as high as 80%.

 

LED is Versatile

Let’s start with an overview of the features that make LED lighting suitable, and in many cases superior, for nearly any industrial lighting application. Well-designed LED luminaires are:

White and bright. Far from the dim, bluish-green flashlight you keep in your glove compartment, today’s industrial LED luminaires provide extremely high-quality light, comparable to any other lighting technology.

Long-lived. Correctly designed, LED luminaires offer up to 60,000 hours of illumination, with no droop and no penalty for frequent on/off cycles.

Highly directional. LED luminaires can be configured to produce virtually any horizontal and vertical distribution of light, from illuminating a tall, narrow fence line for security purposes to providing area lighting that allows production crews to work efficiently and safely.

Resistant to shock, vibration and corrosion. LEDs can be used in environments where other technologies fail — either prematurely or catastrophically.

Cold start capable. LEDs provide instant on and instant restrike capabilities to –40°C, with no warm-up time to full brightness.

Non-damaging. LEDs produce none of the harmful UV or IR radiation often associated with other lighting sources.

Safe for hazardous locations. Available LED luminaires are rated for use in areas where flammable gases and vapors are present under conditions defined by NEC Class I, Division 2 and IEC Zone 2.

Superior for difficult locations. LED lighting is often the best choice for areas with low clearance, severe weather conditions, excessive moisture or dust, corrosive atmospheres, and high ambient temperatures.

Low maintenance. Rugged and long running, LED lighting requires very little maintenance. If you choose a luminaire with an intelligent modular design, even end-of-life replacement of components becomes quick and simple.

With all these benefits, we still haven’t touched upon three of this technology’s most remarkable qualities: LEDs are efficient and environmentally friendly and cool. Because there are many misconceptions in the popular imagination and even in industry literature, we’ll devote the rest of this article to examining these three unique qualities of LED lighting.

Figure 3. While the surface and beam of an LED produce little heat, the T junction can become quite hot.

 

Figure 3. While the surface and beam of an LED produce little heat, the T junction can become quite hot.

 

LED is Efficient

The main driver for LED adoption is efficiency. Achieving the lighting levels required for a particular application at the lowest possible energy input becomes critical as energy costs rise and as government regulations clamp down on waste of energy resources.

Defining efficiency

Comparing the efficiency of dissimilar systems can lead to confusion. Consider the following specifications (see figure 1):

A 175 watt pulse start metal halide lamp requires 208 watt input power to the luminaire (the excess power is lost in the luminaire’s ballast). The light output for each lamp is 17,500 lumens, and the average lighting when four luminaires are installed at a 13-foot height over a 100 x 15 foot walkway is 5.67 foot-candles. Total input power for the installation is 832 watt.

A 165 watt QL induction lamp requires 165 watt power to the luminaire. The light output for each lamp is 12,000 lumens, and the average lighting when six of these luminaires are installed over the walkway is 6.34 foot-candles. Total input power for the installation is 990 watt.

A 48 x 1.7 watt LED array requires 98 watt input to the luminaire (the excess power is lost in the driver). The light output for the luminaire is 5,400 lumens (this figure cannot be compared directly with lumens from a conventional lamp). The average lighting over the walkway when four of these luminaires are installed is 9.55 foot-candles. Total input power for the installation is 392 watt.

It may be tempting to look at the input power to the entire system versus the power actually consumed by the lamps, and to conclude that LED is the least efficient of the three. That would be a mistake. The important comparison is input power versus actual illumination at the point where it’s needed. In this scenario, LEDs are more than twice as efficient, providing brighter illumination at less than half the power consumption of either QL induction or pulse start metal halide.

Comparing lumen output

It may also be tempting to conclude that LEDs are less efficient than the alternatives based on the lumen figures given in the previous bullet points — 17,500 for the pulse start metal halide lamp, 12,000 for the induction lamp, and 5,400 for the LED luminaire. These figures cannot be directly and fairly compared. Figure 1 gives a lumen value of -1 for the LED luminaire. This value is used by our photometric software to distinguish LED from other types of lighting in its calculations to produce results that are valid across these very different technologies.

An LED luminaire incorporates an array of point sources that direct light precisely where it’s needed, with very little scattering or loss. Light distribution is controlled by the placement of LEDs, as well as by efficient use of optics that take advantage of the focal point presented by each individual LED. By contrast, conventional lamps cast light in every direction, and the luminaires incorporate hoods, reflectors, and lenses to direct light to where it’s needed and shade areas where it’s not. Due to scattering and absorption, only 40 percent of the available light reaches its intended destination, versus up to 80 percent for an LED luminaire (see figure 2).

A lumen rating calculated by totaling the light output of all LEDs in the luminaire is simply not comparable to a lumen rating for a lamp based on measurement of light output in all directions. Most light from the lamp never reaches its destination, while nearly all the light from an LED does, and this is why even our estimation of 5,400 lumens for a 48-LED array shouldn’t be used for purposes of comparison. LED is inherently incomparable with other lighting systems in terms of lumen output. What matters is how much light reaches the intended surface, and at what energy cost. In these terms, LED is the clear efficiency leader.

LED is "Green”

Properly designed, an LED luminaire produces a pleasant and eminently usable white light. But LED is also remarkably "green.” Several factors combine to give LED the smallest environmental footprint of any manufactured source.

LED is energy efficient

The most important "green” feature of LED is its energy efficiency. By choosing LED luminaires, you can significantly reduce your energy costs for lighting. Because 70 percent of electricity in the U.S. is produced by burning fossil fuels, your choice is also likely to cut emissions of greenhouse gases and toxic pollutants by half. Your total energy consumption is likely to be even lower when you consider that many buildings will require less cooling due to the lower operating temperature of LEDs. Consuming less energy is not only good for the environment; it’s also good for your company’s public image.

LED is Non-Toxic

LED lighting is also the only non-incandescent lighting source that contains no mercury. This eliminates any chance for mercury to escape into the environment either in operation or after disposal. Combined with LED’s inherent durability, the lack of mercury makes installation, maintenance, and disposal much easier. There are no special handling requirements. The extended lifetime of LED compared to most other lighting sources means less material being disposed over time — another ecological benefit. If you’re careful to choose a manufacturer that uses lead-free solder, you can be sure that no toxins are entering the environment when components do finally reach end-of-life.

Choose ENERGY STAR®- certified products for best performance

For manufacturers and customers alike, ENERGY STAR certification provides the benefit of knowing that products have been tested and approved by a reputable third-part organization to ensure they meet stringent environmental and operational requirements. Not all manufacturers seek or obtain this certification, which means they’re depending on customers to trust their claims and specifications without objective corroboration.

More than just meeting energy consumption requirements, ENERGY STAR certification means that a product has been tested to ensure the highest quality. Simply put, this government created certification body will not approve luminaires that don’t meet customer expectations, no matter how energy efficient they may be. Among many other requirements, ENERGY STAR certification ensures that LED lighting luminaires:

Use at least 75 percent less energy than equivalent incandescent lighting, and provide efficiency as good as or better than fluorescent lighting

Offer brightness equal to or greater than other technologies, with good distribution over the lighted area

Provide constant light output that decreases only near the end of the product’s rated lifetime

  • Provide excellent color quality, with a shade of white light that remains clear and constant over time
  • Turn on instantly, and use no power when turned off other than a maximum of 0.5 watts in the control gear

LED is Cool

If you own an LED flashlight, you know that LEDs put out very little heat. No matter how bright, you can touch the light source indefinitely with no discomfort. Moreover, LEDs produce no harmful ultraviolet or infrared radiation. These properties offer many benefits — lowering cooling costs, simplifying maintenance, prolonging product life, avoiding damage to eyes and sensitive equipment, and providing a margin of safety in hazardous environments.

Industrial LED luminaires do produce some heat

Unlike a battery-powered flashlight, however, AC powered LED technology does produce a significant amount of heat outside the beam. It’s important to understand why this is so and how to manage the heat properly.

LEDs operate naturally on direct current. To light an LED on an AC circuit without destroying it, you need a driver that converts AC to DC and steps the voltage down from 120 Vac (or more) to 24 Vac. Unlike a flashlight battery, the output current is at very high amperage — much higher than the milliamps required to light the LED. This current is fed into the T junction at the rear of the LED (see figure 3).

The T junction can be compared to a tiny nozzle mounted on the end of a large fire hose. In stepping the input current down to meet the requirements of the LED, the T junction absorbs a substantial amount of energy — similar to the friction a large volume of water under high pressure creates when it meets with the constriction of a nozzle. This energy is released as heat. While the beam of an LED luminaire may be cool, the back side of the LED array can become quite hot. The T junction is the hottest spot on the luminaire.

Accurately determining its maximum temperature is crucial when rating products for use in the potentially flammable atmospheres of oil refineries, paper mills and other manufacturing environments.

The other main heat-producing component is the driver inside the luminaire unit, which is analogous to the ballast compartment in conventional lighting systems. The driver is a solid state device and as such it needs to operate within a specified case temperature rating.

Managing heat

Properly managing the heat generated within the LED luminaire is important for three primary reasons:

  • Excess buildup of heat at the T junction can degrade the phosphor and reduce lamp life
  • Excess heat at the driver unit can also reduce product life
  • Inadequate heat management can limit the range of ambient temperatures for which the product can be specified.

Luminaires rated for maximum ambient temperatures below 55°C cannot be used in many areas of the world (for example, the Middle East) and in many specific applications (for example, smelting and casting).

A properly designed LED lighting luminaire will have a large external heat sink — often visible as a series of bare or powder-coated metallic fins surrounding the LED array itself. This heat sink is designed to pull heat away from the T junctions on each LED as well as from the driver housing. After several minutes of operation, the heat sink will become noticeably warm to the touch, even while the beam itself remains cool.

Prominent heat sinks may be unfamiliar to most people who are used to seeing LEDs in lower current applications such as signal lights, or outdoor luminaires that benefit from free flow of air and nighttime temperatures. For industrial lighting applications, when circuitry and lamps are housed in an enclosed and gasketed or explosion-proof luminaire, these heat sinks are critical. They ensure that LEDs achieve their full 60,000 hour lifespan with no degradation in the quality of light. The heat sink allows luminaires to operate reliably in temperatures ranging from –40°C to as high as 55°C.

Overdriving LEDs

Even with adequate heat sinking, good thermal management requires that luminaires be designed with the optimum number of LEDs to achieve the desired lighting levels. It’s possible to achieve a dramatically whiter, more intense light by adding more LEDs than the optimum number. This strategy will inevitably overdrive the system, reducing lamp life, damaging the phosphors, and causing a noticeable color shift or "droop.”

When too many LEDs are incorporated into the design, what began as an impressive display of white light may shift to an unacceptable color within weeks, and may die altogether within a few thousand hours of operation.

Locating and measuring hotspots

Luminaires designed for use in hazardous atmospheres must be rated according to stringent requirements to ensure that a spark or hotspot doesn’t ignite the atmosphere. If an internal ignition occurs it should not be allowed to escape from the luminaire into the surrounding atmosphere.

Construction and testing standards for these luminaires are controlled by the IEC, NEC, and other standards and testing bodies. For the most part the standards are well understood and consistent, but LEDs require a new approach to temperature rating.

Conventional wisdom based on more established technologies suggests that the hotspot is likely to occur on the surface of the lamp, but as we have seen this is not true with LEDs. The hotspot is at the T junction, which is sealed inside the LED assembly. The T junction is impossible to reach with a thermocouple in order to take a temperature reading directly.

Currently, different manufacturers and testing bodies use different methods to place the thermocouple as close as possible to the T junction, as well as different methods to analyze the results and estimate the true hotspot temperature.

We expect to see a single, accepted standard emerge for temperature rating of LED luminaires. In the meantime we suggest talking with the manufacturers whose products you are considering, and asking how they arrive at their temperature ratings and how much margin of error is built into the results. Because LED luminaires tend to have a lower temperature rating than most of the alternatives, you should be able to find a suitable product rated at a significantly lower temperature than the safety threshold for most applications.

LED is the Future

LED industrial lighting is here today, and it’s here to stay. The benefits it provides simply can’t be ignored, either by end users or manufacturers. Even local and national governments are taking notice of the benefits as they increasingly focus on the problems of energy consumption, greenhouse gases, pollutants, and toxic waste.

While LED technology is not the only choice, or in some cases even the best choice, it will rapidly become the leading choice to replace many of today’s energy hungry industrial lighting systems. In the years ahead — as standards become more firm, product lines more established, and customers more conversant with the technology — LED will also become a relatively easy choice. We’re not there yet. We’ve just entered the gates of the golden city, and there’s still a lot to explore.

The important thing is that we’ve seen enough to know where we’re going. The fundamentals are in place, and some very good LED products are already on the market. The knowledge of how LEDs work and the best ways to harness the technology are available. As with anything new, big, and potentially lucrative, a lot of misinformation has been made available as well.

Our goal in this article has been to present the facts you need to know about LED luminaires and to dispel the misinformation. Armed with this knowledge, you should be better prepared to enter the world of LED product evaluation for your own lighting design projects. With a little hands-on experience, you should soon be as comfortable with LED as with any other lighting system.


Read more by Steve Henry

Tags:  Featured  November-December 2012 

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On the performance of arc flash analysis in DC power systems

Posted By Michael Furtak, Thursday, November 01, 2012
Updated: Wednesday, December 12, 2012

Direct current (DC) arcing fault incident energy calculations are presented to assess the level of risk involved when working around high current DC apparatus. The proposed procedure allows evaluation of incident energy and arc flash boundaries, while taking into account as many circuit parameters as possible. These parameters include fixed or variable gap length, system voltage, available fault current, equipment configuration, circuit time constant and evaluated threshold energy for a second degree burn.

DC Arc Steady State Modeling

The resistance load line of the equivalent steady state circuit diagram representing a linear DC supply can be described by Equation (1) below:

V=Vs–I*Rs, (1)

where Vs stands for open source voltage and Rs is system resistance including source and feeders. The applications include battery packs, power converters and chargers, mining sites, public transportation, solar and wind farms, etc. Substituting into the Equation (1) voltage drop across an arc (Varc), arcing current can be resolved as:

Iarc=Isc*(Vs-Varc)/Vs, (2)

where Isc is prospective short-circuit current at the arcing point. It is shown that arc voltage is mainly determined by the arc length, and the voltage is within the 10 to 20V/cm range for arc currents up to the order of 50kA.1 Incident energy exposure for an open-air arc where the heat transfer depends on the spherical energy density is then expressed as:

Einc=Varc*Iarc*tarc/(4*π*D2), (3)

where tarc is the arc duration and D represents the distance from the arc. This formula assumes the radiant heat transfer. Not all of the arc energy will be transferred as radiant heat 2 especially within the short time interval after the arc was ignited. Therefore, the Equation (3) will produce a conservative but safe estimate of incident energy exposure. For the arc in a box, the enclosure has a focusing effect on the incident energy. For the selected enclosure type and test distance,3 the incident energies calculated for enclosures are 2.2 times larger than the incident energies calculated for open air.

Equation (3) written in terms of arc flash boundary, becomes:

AFB=[Earc/(4*π*Et)]0.5, (4)

where Et stands for threshold incident energy to second degree burn 4 evaluated as:

Et=1.2*t0.3,(5)

Figure 1. Sample arcing power and time to 2nd degree burn vs. arcing current at 0.5 meter distance away from arc in open air 600 VDC system.

Figure 1. Sample arcing power and time to 2nd degree burn vs. arcing current at 0.5 meter distance away from arc in open air 600 VDC system.

DC Arc Transient Conditions

The problem of determining the arc flash boundary becomes less trivial when gap is not fixed and distance between anode and cathode is anticipated to increase by separation of the contacts. Also, the arc operates at the intersection of the arc volt-ampere characteristic curve and the resistance load line of the DC circuit. Therefore, the arcing current will stabilize itself at a fixed point on the curve and the arc will dissipate a relatively constant amount of power. However, it’s hard to predict how long it will take for the arcing current to stabilize before the arc burns out or is cleared by the upstream protective device. The load line may intercept the characteristic curve in two locations, but only one point is stable. The stable operating location is the point with the lowest arc voltage. 5

Stokes and Oppenlander 3 demonstrated that there is a minimum voltage needed to maintain an arc. That minimum depends on the current magnitude, gap width, and orientation of the electrodes. This transitional point can be expressed as:

It=10+0.2*Zg, (6)

where the length of the gap, Zg, is expressed in mm., It is measured in amperes. Above that minimum, the arc V-I characteristic can be expressed as: 3

Varc=(20+0.534*Zg)*Iarc0.12, (7)

To find the point where the arc V-I characteristic crosses the circuit load line, solve equations (2) and (7) using the iterative method. As the first approximation, assume Varc is equal to half of the system voltage Vs. Then, follow the steps below:

  1. determine Iarc from Equation (2)
  2. substitute Iarc into Equation (7) to determine new Varc

Cycle through the steps listed above until the answers for Varc converge. Additionally, circuit time constant affects current rise and protective device performance characteristics, thus impacting the arc duration. In this case, time current characteristic of the upstream protective device clearing the fault may have to be adjusted for the time constant. If this occurs, the process of determining the protective device operating time is cumbersome. First, the time-current characteristic of the protective device has to be analytically expressed as a function of the available fault current. A paper by Cynthia Cline6 provides an equation describing the relationship between the effective RMS current, the available fault current, and the number of time constants:

Irms=Iarc*K, (8)

where the K factor is expressed in numbers of time constants n=tarc/tconst:

K=(1 + 2e-n /n - e-2n/2n - 1.5/n)0.5, (9)

This creates a dilemma due to the fact that one cannot determine the arcing time without the RMS value of the arcing current, and one cannot solve for the RMS current without the arcing time represented by the n term in Equation 9. This requires an iterative solution. As a first approximation, begin by assuming that Irms equals Iarc, determining tarc from the analytical expression for the fuse T-C characteristics tarc=f(Irms), determining the number of time constants n and calculating K from Equation 9, substituting its value into Equation 8 to calculate the new RMS current, and then solving for the arc duration again. Once the first approximation of the arc duration has been made, determine the new number of time-constants n, re-calculate the K term and substitute its value into Equation 8. This produces a new Irms. Re-calculate for a new tarc by using the new Irms and continue until the answers converge. Then, Equations (3) through (5) can be utilized to complete the DC arc analysis under the transient conditions.

Figure 2. Simplified block diagram for resolving arcing faults in DC power systems.

Figure 2. Simplified block diagram for resolving arcing faults in DC power systems.

Generalized Solution

With numerous variable parameters on hand, which results in the difficulty to accurately model DC arc and to predict the arc V-I characteristic and thermal behavior, we decided to consider the worst-case scenario leading to an arbitrary burn hazard in the shortest possible time. Figure 1 shows arcing power as a function of variable arcing current for the DC equivalent circuit described by Equation 1. The red line on figure 1 represents time to 2nd degree burn as a function of heat flux.4 Note that the minimum time to 2nd degree burn, as well as any other burn hazard, coincides with the maximum power released by an arc, hence, the maximum heat flux.

For a fuse with an inverse time-current characteristic, the amount of arcing currents is inversely correlated with the fuse operating time, and consequently, with the arc duration. With the decrease of arcing current, power released by an arc will actually increase and reach its maximum value corresponding to the middle point on figure 1. Further decrease in arcing current will lead to a decrease in arcing power and an increase in arc duration time when it takes more time for the upstream protective device to clear the fault. Therefore, there is a minimum amount of time leading to a specified burn severity produced by any given DC arc, and, for the 2nd degree burn on bare skin, that time can be expressed as:

t=[0.015*Isc*Vs/(π*D2*Eb)]-1.43, (10)

where Eb is equal to 1.2 cal/cm2/sec. The Equation (10) assumes rectangular flash pulse, thus producing the minimum time to 2nd degree burn under the specified circuit conditions. It can also be applied for hazards other than 2nd degree burn by selecting a different Eb factor on the right side of the Equation 10. When analytical expression for the protective device clearing the fault time-current characteristic is available, it is possible to examine power and energy released by an arc as a function of arcing current and arc resistance, and to determine maximum damage that can be caused by the arc during the selected time interval. A simplified block diagram on figure 2 describes the proposed approach for calculating incident energies and for determining arc flash boundaries in DC power systems.

Summary

With a better understanding of the DC circuit parameters and the DC capabilities of fuses, modeling DC arcs and selecting appropriate fuses for mitigating arc-flash hazard can be accomplished without much difficulty. The generalized solution presented in this paper considers the worst-case scenario, effectively eliminating the need for accurately predicting arcing gap and arc resistance.

References

1 "Electric Arcs and Arc Interruption.” C.E. Sölver. Chalmers University of Technology. February 2005.

2 "Electric Power Transmission Systems.” 2nd Edition. J. Robert Eaton, Edwin Cohen. Prentice-Hall, Inc.

3 "DC Arc Models and Incident Energy Calculations.” R. Ammerman, T. Gammon, P.K. Sen, J. Nelson. IEEE Transactions on Industry Applications, Vol. 46, No. 5, September/October 2010.

4 "Evaluation of Onset to Second Degree Burn Energy in Arc Flash.” M. Furtak, L. Silecky. Electrical Safety Measures, March/April 2012.

5 "Arcing Faults on Direct Current Trolley Systems.” P. Hall, K Myers and W. Vilchek. Mine Safety and Health Administration.

6 "Fuse Protection of DC Systems.” Cynthia Cline. Annual Meeting of the American Power Conference. April 1995.


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Life Safety Loads Depend on Reliable Power Systems

Posted By Tim Crnko and Mark Hilbert, Monday, September 03, 2012
Updated: Thursday, September 20, 2012

What matters to a person when they are in a facility that has capacity for many people and an emergency situation such as fire, flooding, storms, earthquake, explosion, or merely loss of normal utility electrical power occurs? Naturally, this depends on the situation, but the basic human instinct is to want to escape the event without physical or extreme emotional trauma. We desire safety for our family, ourselves, and others.

In buildings where large numbers of people can assemble, such as office buildings, schools, high rises, hotels, theatres, arenas, and hospitals, there are electrical loads that are intended to provide for human safety in emergency situations. The 2012 NFPA 101 Life Safety Code provides minimum life safety requirements for the design, operation, and maintenance of buildings and structures. Examples include emergency loads such as elevators, emergency lighting, emergency egress lighting, alarm systems, ventilation, smoke control, fire pumps, and more. These life safety loads need to operate when there is an emergency and need to operate as long as possible, even if the building and electrical system supplying these loads are under physical distress. And if a portion of the electrical system is damaged due to fire or other causes, it is imperative to restrict any resultant electrical outage to the minimum portion of the electrical system thereby keeping as many vital loads powered as possible. Lives may depend on these loads.

A key requirement for the electrical systems that power these life safety loads is reliability. It is superior to that typically provided for ordinary loads and thereby increases the probability people can survive or escape during emergency events. The reliability of electrical systems supplying life safety loads and functions is just as important and possibly more so for first responders. Merely relying on the normal system does not provide sufficient continuity of electrical power for life safety. Additional alternate electrical source(s) (in case the normal source is lost) and an electrical distribution system designed, installed, and maintained to be more reliable are necessary. Components such as generators, automatic transfer switches, and circuit wiring with higher reliability features are needed. This increases the cost, space requirements, and design, installation, and maintenance complexity of the facility electrical system. But not having these could mean loss of life or severe injuries if an emergency event occurs.

Figure 1. This overly simplified electrical distribution system one-line depicts the various circuits and panels. Each emergency panel may have one or more life safety type loads or functions with one or many branch circuits for each life safety function.

Figure 1. This overly simplified electrical distribution system one-line depicts the various circuits and panels. Each emergency panel may have one or more life safety type loads or functions with one or many branch circuits for each life safety function.

There is an ever continuing trend to utilize more and increasingly sophisticated life safety and emergency electrical functions. In other words, for facilities where large numbers of people assemble, there are more emergency loads with more complexity and interdependencies. Elevators have long been used for transporting first responders and their equipment. However, now in some cases, elevators are being used for emergency egress of building occupants; the 2012 NFPA 101 has added new requirements for occupant evacuation elevators. Now there are sophisticated public safety communication systems, fire detection and alarm systems, and more. As you walk in the middle of a large unfamiliar building at night ask yourself what you would do if a major fire or explosion ensued and all the lights go out, and none of the life safety loads functioned.

Figure 2. Cascading overcurrent protective devices will result in unnecessary loss of power to other life safety loads.

Figure 2. Cascading overcurrent protective devices will result in unnecessary loss of power to other life safety loads.

The 2011 NEC has minimum installation requirements for the electrical systems supplying these vital life safety loads. These minimum requirements provide the baseline for the electrical system reliability. Systems can be designed and installed for more reliability than the NEC requirements, but the minimum NEC requirements must be met and not compromised.

The bottom line is that if it is your family at the top of a high rise building during a major fire, their path of egress to safety relies heavily on the electrical system. Whether the normal source or the emergency source is supplying the power to the life safety loads, come "hell or high water,” your family’s fate may very well be in the hands of the electrical system. If they are on the 20th floor and have to exit via a stairway, will the egress lighting be operational to illuminate their pathway? Will the smoke control system keep the stairway free of smoke so they can survive? Will the public safety communication system be powered to deliver vital messages to assist in their journey to exit the building or to a safe location? Will the elevators be powered so the first responders and their equipment can quickly get to where they need to be and they can move quickly to other locations? The answer to these questions lies within the integrity of the "emergency system.”

If fire, smoke, or physical damage to the building causes a fault in the emergency electrical system, will the fault be localized to only the faulted circuit, or will multiple levels of overcurrent protective devices cascade open and unnecessarily cause loss of power to life safety loads? Remember, it could be your family relying on the integrity of the electrical system to ensure their pathway to safety.

The authority having jurisdiction (AHJ) has an important role. They very well could be the last line of defense against an electrically compromised pathway to safety. From an enforcement standpoint, those responsible for approving the electrical installation have the responsibility to ensure the minimum requirements are met for these vital life safety systems. If AHJs are able to review the plans and installations and ensure code-compliance, your family has an increased probability of coming home if ever they are caught in a building when an emergency event occurs. In some cases, the AHJ has to establish the "interpretation of the rules” per NEC 90.4 which is an especially significant responsibility when it concerns the emergency electrical system.

It is important to mention that besides the NEC and NFPA 101, there are other applicable codes and standards that are not mentioned in this article but that have relevant requirements for specific life safety functions, systems, or loads.

Systems Vital for Life Safety

The societal demands upon modern building life safety are necessitating more life safety systems, more interdependency of various electrical functions which are supplied by emergency systems, and greater reliability.

Elevators are an example. In normal conditions elevators are a convenience to move people vertically in a building. Over the decades, we have been educated not to use the elevators during fires. However, elevators can have the provision for first responders to take control of elevators for improving their speed of response. In some cases, elevators might only be supplied by the normal electrical system and have no provision for emergency power. In other cases, elevators may be on the emergency system and therefore supplied by either the normal or emergency source, depending on the circumstances.

However, in emergency conditions elevators are now permitted to serve as occupant evacuation elevators (2012 NFPA 101 7.14) if approved by the AHJ and if all requirements are met (includes NFPA 101, NEC, and others). The NFPA 101 requirements include the emergency command center continuously monitoring and displaying the elevators, elevator lobbies, elevator machine rooms, and status of many related functions serving the elevator system. The following are a few such interdependent functions powered by the emergency electrical system. The lobbies of occupant evacuation elevators must be equipped with a status indicator display system to communicate visually to occupants the condition of use: (1) normal use, (2) available for occupant evacuation, or (3) out of service – use the stairs.

If elevators are used for occupant evacuation, then the building must be protected throughout with a fire alarm system and a voice/alarm communication system with capability to give voice directions on a selective basis to any floor. In addition, occupant evacuation elevator lobbies must be equipped with a two-way communication system to permit communications between persons in the elevator lobby and the emergency command center or another designated location. This illustrates the level of sophistication modern building life safety systems may have; there are multiple interdependent systems vital for human safety that are powered by the heart of the electrical system, the "emergency system.” Losing one or more of these systems reduces the probability the occupants will survive.

Photo 1. This photo was taken by Mark Hilbert after an earthquake in Hawaii. The entire island was without power because the utility generators sensed the movement and shut down. The only thing illuminated in the entire hotel was the stair tower.

Photo 1. This photo was taken by Mark Hilbert after an earthquake in Hawaii. The entire island was without power because the utility generators sensed the movement and shut down. The only thing illuminated in the entire hotel was the stair tower.

There are many other life safety electrical loads or systems that may be deployed in a building. These can include fire pumps, emergency lighting, egress lighting, smoke control systems, fire detection and alarm systems, communications systems, video systems, ventilation, HVAC for specific applications, monitoring various electrical functions and other functions.

Reliable Electrical Power

Reliable power supply and reliable electrical circuits for life safety loads are vital. The NEC has specific requirements for fire pumps in Article 695 and elevators in Article 620. In addition, Article 700 Emergency Systems, Article 701 Legally Required Systems, and Article 708 Critical Operations Power Systems provide requirements for electrical distribution systems that demand more reliability than normal systems.

Per NEC Article 700, the life safety loads and systems are powered by the normal electrical source and, in addition, with one of the type emergency electrical power sources complying with 700.12. So in simple terms, life safety loads or functions are powered from an emergency electrical distribution system which is supplied by a normal source and an emergency source. There can be a wide variance in the electrical distribution system layouts based on the building type and life safety loads or functions required by the AHJ or by chosen design. Figure 1 is an overly simplified electrical distribution system one-line depicting the various circuits and panels. Each emergency panel may have one or more life safety type loads or functions with one or many branch circuits for each life safety function. So what makes NEC Article 700 emergency systems more reliable than normal NEC electrical systems? In addition to complying with Chapters 1 – 4 of the NEC, emergency systems must comply with NEC Article 700 which can supplement or modify Chapters 1 – 4. In addition, there may be requirements applicable for an emergency system from Chapters 5 for Special Occupancies, 6 for Special Equipment, and other Chapter 7 articles for Special Conditions. The following discussion will highlight some of the key Article 700 requirements that provide the increased reliability to power life safety loads.

700.3 Requires AHJ witnessed testing of the emergency system upon installation and periodically.

700.4 Capacity and rating for simultaneous operation of all loads. All equipment must have short-circuit ratings equal to or greater than the available fault current and all overcurrent protective devices must have interrupting ratings greater than the available fault current.

700.5 Automatic transfer switches and all transfer equipment shall be identified for emergency use.

700.10 All boxes and enclosures must be permanently marked as part of an emergency circuit or system. Emergency circuit wiring must be separated from other wiring. Wiring must be located to minimize failures due to adverse conditions such as flooding, fire, etc. There are special fire protection requirements for some occupancies which may require a two-hour fire rating.

700.12 If normal power is lost, emergency power shall be available to loads within 10 seconds. This section provides the type of alternate power sources that may be used. The specific type of alternate source utilized is typically based on the performance required by the NEC and other codes and standards predicated on the type occupancy and type of service required.

700.15 Emergency lighting branch circuits can only supply lighting designated as required for emergency use.

700.16 The failure of one lighting element must not result in total darkness to any space requiring emergency illumination. This is an extremely important element (no pun intended) that ensures that while under emergency conditions, the objective of avoiding spaces without illumination is met.

700.20 Only authorized personnel shall have control of emergency lighting.

700.25 Only authorized personnel may have access to emergency branch circuit overcurrent protective devices.

700.26 Ground fault protection with automatic disconnecting means, as required by 215.10, is not required for the alternate emergency source. This is an important permission since this relegates the delivery of power to life safety loads at a higher priority than the damage resulting due to a ground fault. However, if this permission is granted then ground fault indication is required in accordance with 700.6(D).

700.27 "Emergency overcurrent protective devices shall be selectively coordinated with all supply side overcurrent protective devices.” This requirement is especially important when the emergency is a fire, explosion, earthquake, or similar event which may increase the risk of a fault on a circuit. Fires may cause the ionized gases to initiate a fault in equipment or the resulting high temperature may result in a short circuit. Earthquakes and explosions can cause faults in equipment and circuits as well. If the installed overcurrent protective devices are not selectively coordinated for all levels of available fault current, a fault on one part of the system may unnecessarily cascade two or more levels of overcurrent protective devices upstream. Cascading overcurrent protective devices will result in unnecessary loss of power to other life safety loads.

See figure 2. A branch circuit fault such as X1 or X2 should only be cleared by the branch-circuit overcurrent protective device (1 or 1A, respectively). No feeder overcurrent protective devices upstream should open for a branch-circuit fault (X1 or X2). If a branch-circuit fault X1 unnecessarily opens the feeder 2 overcurrent protective device, an entire emergency panel will be without power versus only the life safety load(s) on the faulted branch circuit 1. Or if branch-circuit fault X2 unnecessarily opens the feeder 2A overcurrent protective device, a whole bank of elevators will unnecessarily be without power versus only the one elevator on the faulted branch circuit. If the cascading goes even higher in the system, such as when feeder 3 overcurrent protective device unnecessarily cascades open for a branch-circuit fault (X1 or X2), all the emergency loads will unnecessarily be without power. The unnecessary opening of overcurrent protective devices can jeopardize the life safety of the building occupants and first responders who may need those specific life safety loads.

Summary

People’s lives depend upon the emergency power sources and emergency distribution systems delivering power to life safety loads during emergency situations. In essence, emergency systems are "insurance” that people are more likely to survive an emergency event, but there is a price to pay for this reliability. All the extra electrical equipment it takes to comply with NEC Article 700, Emergency Systems, has costs plus the additional cost for the associated engineering, installation, and maintenance. However, the bottom line is that it’s going to be someone’s family member on the 20th floor of that building during a fire, earthquake, explosion, or other emergency situation that has to find a pathway to safety. If it was your family member, wouldn’t you want these systems designed, installed, inspected and maintained as required?


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Magnetic Motor Starters as Controllers — A comparison of NEMA- and IEC-type devices

Posted By Stephen J. Vidal , Monday, September 03, 2012
Updated: Thursday, September 20, 2012

NEC Article 100 defines a controller as "a device or group of devices that serves to govern, in some predetermined manner, the electric power delivered to the apparatus to which it is connected.” Section 430.2 gives a more motor-specific definition: "For the purpose of this article [Article 430], a controller is any switch or device that is normally used to start and stop a motor by making and breaking the motor circuit current.”

The magnetic motor starter is such a controller and utilizes electromagnetically operated contacts that start and stop the connected motor load. A control circuit with momentary contact devices connected to the coil of the magnetic motor starter performs this start and stop function. A three-pole full-voltage magnetic motor starter is made up of the following components: set of stationary contacts, set of movable contacts, pressure springs, operating coil, stationary electromagnet, set of magnetic shading coils, and the moving armature.

It is also important to remember that a magnetic motor starter is a contactor that has the addition of an overload relay assembly that provides running overload protection to the motor. Selection of the thermal overload relay is done using the manufacturer’s table included with the magnetic motor starter. It is always important to know the full load current (FLC) of the motor, the service factor (SF) of the motor, and the ambient temperature in which the equipment is being operated. Thermal units are based on an ambient temperature of 40° C (104° F).

Types of starters

Magnetic motor starters are commonly available as full-voltage (across-the-line), reduced-voltage, and reversing. A full-voltage or across-the-line magnetic motor starter applies full voltage to the motor, which means it is designed to properly handle the levels of inrush current that will develop as the motor is started (see figure 1).

Figure 1. Full-voltage (across-the-line) magnetic motor starter

Figure 1. Full-voltage (across-the-line) magnetic motor starter

Reduced-voltage starters are designed to limit the effects of inrush current during motor startup. These are available in electro-mechanical and electronic formats.

Figure 2. Full voltage reversing starter

Figure 2. Full voltage reversing starter

Reversing starters are designed to reverse shaft rotation of a three-phase motor. This is accomplished by interchanging any two-line conductors that supply the motor load. The reversing magnetic motor starter features a forward and a reverse starter as part of the assembly (see figure 2). Electrical and mechanical interlocks are provided to ensure only the forward or the reverse starter can be engaged at any given time, but not at the same time.

Comparison of NEMA and IEC starters

In this article we will focus on how NEMA (National Electrical Manufacturers Association) and IEC (International Electro-Technical Commission) relate to the selection and application of magnetic motor starters.

NEMA magnetic motor starters are available in various voltage and horsepower ratings with the following designations: sizes 00 through size 9, consecutively. These NEMA sizes classify a magnetic motor starter by voltage and maximum horsepower. Examples of AC voltages include 24V, 120V, 208V, 240V, 277V, 480V and 600V varieties. The magnetic motor starter is also offered in different types of enclosure depending on the environment in which the equipment will operate, not to mention DC coils. Typical protective enclosures are NEMA 1 (general purpose), NEMA 4 (watertight), NEMA 12 (dust-tight) and NEMA 7 (hazardous location).

IEC-style magnetic motor starters are usually available in a modular format with a contactor and an overload relay. Three-phase contactors are available in 208V, 230V, 460V and 575V variety with corresponding maximum horsepower ratings. IEC magnetic motor starters are often supplied as part of original equipment manufacturer (OEM) equipment, as are NEMA starters.

If we compare the NEMA magnetic motor starter to the IEC magnetic motor starter, we would notice the following differences:

IEC device typically is physically smaller than the comparable NEMA device but not in all cases, especially in larger sizes.

The life cycle can be different between NEMA and IEC devices. Performance evaluation between NEMA and IEC, as well as variances in how manufacturers develop the data (not validated by 3rd parties so test methods could vary greatly). The general safety performance of either IEC or NEMA devices is evaluated by a 3rd party testing agency in North America. The EU does permit self-certification, but manufacturers of NEMA devices also use self-certification for NEMA-specific performance characteristics. A NEMA controller is typically from an OSHA accredited lab, while an IEC device may be self-certified, with a CE mark, or certified by a lab that may not be OSHA accredited. NEMA starters can now be used in conjunction with electronic/solid state overload relays that are adjustable.

IEC device has an adjustable overload relay assembly, while the comparable NEMA device has a fixed and removable overload relay assembly. In addition, NEMA devises can be used in conjunction with electronic/solid state overload relays that are adjustable.

IEC device should normally be protected with fast-acting current-limiting fuses, while the NEMA device can be protected with conventional time-delay fuses, but this varies from product to product and from manufacturer to manufacturer.

Many IEC and NEMA devices are designed for use with conventional (non–current-limiting) fuses and circuit breakers, at least for standard fault SCCRs. Fact-acting, current-limiting may be used for high fault SCCRs and/or Type 2 coordination.

The end user should carefully consider all these requirements before making the decision to install a NEMA magnetic motor starter or an IEC magnetic motor starter in their specific application.


Read more by Stephen J. Vidal

Tags:  Featured  September-October 2012 

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Selective Coordination of Emergency Systems — Taking the mystery out of enforcement

Posted By Chad Kennedy, Monday, September 03, 2012
Updated: Thursday, September 20, 2012

Selective coordination of the emergency system is intended to provide a high level of reliability and continuance of supply needed for systems providing emergency functions. As with all electrical installations, an effective plan review and installation inspection of the overcurrent protective devices (OCPDs) coordination for emergency systems is fundamental in approving and inspecting such systems. In addition, understanding which circuits require emergency systems also must be considered. Chapter 27 in the International Building Code (IBC) establishes a number of occupancies and systems that require emergency power such as egress illumination, exit signs, and hazardous materials occupancies. Let’s start by looking at the foundational elements for selectivity found in the NEC.

The 2011 NEC defines selective coordination in Article 100 as…

Coordination (Selective). Localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by the choice of overcurrent protective devices and their ratings or settings.

In layman’s terms, selective coordination means that only the overcurrent protective device nearest to a fault should clear the fault. This applies to all fault types: overload, ground fault, and short circuit.

For emergency systems, the requirements for selective coordination are provided in NEC 700.27.

700.27 Coordination. Emergency system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices.

The "mystery” of selective coordination compliance can be easily overcome with training. Where desired, current staff capabilities can be expanded with education and experience and several OCPD manufacturers have excellent programs to assist in this area. Although it is not necessary to understand the myriad of devices and equipment considered in a selective coordination analysis, enforcers intending to review coordination designs should understand the types of documents which should be supplied and how to interpret them.

How do I get started? From an enforcement perspective, there are two basic paths which can be taken. A community that has a plan review department often has the expertise to understand and review the coordination documents while smaller communities without plan review may have a policy which relies solely on the designer or professional engineer to provide the appropriate documentation for field inspection of settings.

Performance Level

It is important to remember that the NEC requirements apply to the installation; however, the performance requirements come from other documents. In addition to specifying which systems must have emergency power, Chapter 27 of the 2012 International Building Code requires compliance with NFPA 110 in Section 2702.1.

IBC 2702.1 Installation. Emergency and standby power systems required by this code or the International Fire Code shall be installed in accordance with this code, NFPA 110 and 111.

Health Care facilities establishes the minimum performance requirements for Healthcare Systems. Photo courtesy of John Watson

Health Care facilities establishes the minimum performance requirements for Healthcare Systems. Photo courtesy of John Watson

NFPA 110-2010, Standard for Emergency and Standby Power Systems, sets the minimum performance requirements for Emergency Systems and NEC Article 700 specifies the material and process associated with putting equipment in place and making it ready for use in accordance with the specified performance requirements. NFPA 110 Section 6.5.1 requires OCPDs be coordinated to optimize selective tripping and A.6.5.1 recognizes there are certain systems which require practical limits or levels.

NFPA 110, 6.5.1 General. The overcurrent protective devices in the EPSS shall be coordinated to optimize selective tripping of the circuit overcurrent protective devices when a short circuit occurs.

NFPA 110, Annex A, A.6.5.1. It is important that the various overcurrent devices be coordinated, as far as practicable, to isolate faulted circuits and to protect against cascading operation on short circuit faults. In many systems, however, full coordination is not practicable without using equipment that could be prohibitively costly or undesirable for other reasons. Primary consideration also should be given to prevent overloading of equipment by limiting the possibilities of large current inrushes due to instantaneous reestablishment of connections to heavy loads.

NFPA 99-2012, Health Care Facilities Code, establishes the minimum performance requirements for Healthcare Systems and NEC Article 517 specifies the material and process associated with putting equipment in place and making it ready for use in accordance with the specified performance requirements. NFPA 99 clauses 6.4.2.1.2, 6.5.2.1.1 and 6.6.2.1.1 set the performance requirements for Types 1, 2, and 3 essential electrical systems with additional explanation provided in Annex A clauses A.6.4.2.1.2, A.6.5.2.1.1 and A.6.6.2.1.1.

NFPA 99, 6.4.2.1.2Selective Coordination. Overcurrent protective devices serving the essential electrical system shall selectively coordinate for the period of time that a fault’s duration extends beyond 0.1 second.

NFPA 99, Annex A, A.6.4.212. It is important that the various overcurrent devices be coordinated, as far as practicable, to isolate faulted circuits and to protect against cascading operation on short-circuit faults. In many systems, however, full coordination could compromise safety and system reliability. Primary consideration also should be given to prevent overloading of equipment by limiting the possibilities of large current inrushes due to instantaneous reestablishment of connections to heavy loads.

While these performance requirements provide the minimum acceptable level, many system designers and engineers will design to obtain higher levels. It is also important to note that some jurisdictions across the country have set specific requirements for the qualifications of selective coordination design personnel and set performance levels which must be followed.

Installation Inspection

Reviewing the coordination documents is just the beginning, ensuring that the installation matches the coordinated design can be an equally challenging hurdle once the equipment has been installed. Manufacturers typically ship equipment with the circuit breaker settings at minimum levels and fusible disconnects without fuses installed. Depending upon the system design, there may be other adjustable devices such as ground-fault relays, circuit protection relays, zone-selective interlocking and energy-reducing maintenance systems with required settings and adjustments. Proper device verification for each circuit breaker or fuse and the settings for any adjustable devices are essential to the performance of the system. A systematic approach using the emergency system one line diagram and the selective coordination documentation is required to perform the system inspection including device type, and settings.

Maintaining Coordination

Since the selective coordination is device and settings dependent, how long will the system be coordinated after inspection? Replacement of fuses or circuit breakers with different types or from a different manufacturer has an impact on the selective coordination of the system. It is important that the maintenance staff understand these constraints and communicate this to their staff. In some cases, marking should be added to provide this communication at the device to ensure that quick response actions don’t impact the coordination by installation of the wrong fuse or breaker.

Summary

Key installation items to verify:

Compliance begins with understanding where emergency power is required. The IBC, Chapter 27, specifies systems and occupancies which must have emergency power.

Determination of the required performance level utilizing NFPA 110, NFPA 99 and any local jurisdictional rules.

A selective coordination study and resulting documents providing device details. Simply walking through and looking at the system devices will not verify the coordination unless a study has been completed.

Ensure adjustable trip settings for the system devices are appropriately set.

When using ratio tables for fuses or selectivity table for circuit breakers, confirm all of the fuses and breakers in the system are the appropriate size, type and from the same manufacturer.

Check the ground fault and other protection relay adjustments and settings.

Consider recommending markings to communicate proper adjustment of breaker settings, and replacement of fuses with specific manufacturer brand and type.

Selective coordination of emergency systems may seem like a difficult task but like many worthwhile challenges the most difficult step is getting started. The life safety importance of emergency systems warrant the performance and installation requirements provided in NFPA 99, NFPA 110 and NEC Article 700. Understanding the codes and standards requirements along with any jurisdictional regulations form the foundation for plan review and installation inspection of these systems. The key implementation items provide areas to verify and potential maintenance concerns to consider as the system is inspected.


Read more by Chad Kennedy

Tags:  Featured  September-October 2012 

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