Posted By Leslie Stoch,
Wednesday, May 01, 2013
Updated: Friday, April 26, 2013
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The Canadian Electrical Code’s long-winded definition of grounding is shown as: "a permanent and conductive path to the earth with sufficient ampacity to carry any fault current liable to be imposed on it, and of sufficiently low impedance to limit the voltage rise above ground and to facilitate the operation of the protective devices in the circuit.” This article discusses a number of permissible grounding requirements and methods covered by the Canadian Electrical Code.
As you no doubt noticed, the definition covers a lot of ground (excuse the pun), as it includes all of the electrical code requirements, including that grounding must:
- be permanent and continuous;
- carry available fault currents without failure;
- have sufficiently low impedance to ensure
- that voltage rise during a ground fault will
- not cause damage to components such as sensitive electronic devices; and
- ensure that fuses and circuit-breakers react
- quickly enough to prevent electrical failures,
- fires and shock hazards.
In some cases, the Canadian Electrical Code does not require that all electrical circuits be solidly grounded. In others, the CEC prohibits it. Rule 10-108 specifies that circuits supplying electrical arc furnaces (such as a scrap metal melting furnace) need not be grounded. Rule 10-110 specifies that circuits supplying cranes operating above highly flammable fibres in Class III hazardous locations must not be grounded. This provision reduces the probability of arcs and sparks along the crane rails and the current collector, thereby limiting the risk of a flash fire. Rule 10-112 permits ungrounded circuits supplied by a transformer incorporating a grounded faraday shield between the primary and secondary windings when permitted by other rules or in special cases to prevent electrical accidents (underwater swimming pool speakers, for example).
We are all at ease with solidly grounded electrical systems. They provide the benefit of limiting system voltages to ground and minimizing voltage stress on wiring and electrical equipment insulation. Solidly grounded systems may experience high ground fault currents, but when correctly arranged, faults are quickly detected and removed by fuses or circuit-breakers before there is damage. In an industrial environment, shutting down during a ground fault may be impracticable, and therefore other grounding methods are recognized in the Canadian Electrical Code. Rule 10-106(1) requires that except where otherwise specified, 120/240-volt and 120/208-volt AC systems or circuits that include a neutral conductor must be grounded.
Ungrounded delta systems don’t require shutting down during a single-phase ground fault since they have no reference to earth. However, they come with risk of equipment damage as well as personal safety risks when a second phase becomes inadvertently grounded. In addition, overvoltages tend to shorten the lives of electrical equipment. Rule10-106(2) requires that ungrounded delta systems must be equipped with ground fault detection devices such as ground indicating lights to ensure that inadvertent grounds are removed as quickly as possible. But you know what happens to those — the indicating lights burn out and are not promptly replaced, leaving people and equipment at risk.
A nice compromise is resistance grounding which permits operation during a single-phase ground fault. Resistance grounding offers a number of important advantages. It limits ground fault currents by connecting a grounding resistor between the electrical system neutral and the system ground electrode and thereby:
- minimizing damage to electrical wiring and equipment;
- reducing mechanical stresses;
- reducing arc flash and arc blast hazards ;
- controlling overvoltages; and
- no shutdown required during a ground fault.
Finally, effective grounding helps ensure that faults are quickly removed. Rule 10-500 defines effective grounding. Sound familiar? But what’s this about "impedance sufficiently low”? Appendix B provides an answer: impedance of the ground fault path should be sufficiently low so as to permit at least five times the setting of the circuit overcurrent devices to flow during a ground fault. For example, for a 400-ampere circuit, at least 5 times 400 amperes or 2000 amperes must be allowed to flow during a ground fault.
As with earlier articles, you should always check with the electrical inspection authority in each Province or Territory as applicable for a more concise interpretation of any of the above.
Read more by Leslie Stoch
Posted By Randy Hunter,
Wednesday, May 01, 2013
Updated: Friday, April 26, 2013
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Article 250 is the largest article in the National Electrical Code. It is often the most dreaded by those new to the code, and sometimes even by those who have dealt with the code for years. Some of the terminology is confusing and conceptually difficult to follow. In keeping with the Combination Inspector emphasis of this series of articles, we will cover those items which I have previously taught to inspectors who weren’t electrical by trade. In doing so, we will not cover every section of Article 250, but concentrate on those that are used most commonly by multi-trade inspectors.
Photo 1. Here is a very small sampling of some of the devices designed for grounding connections. Please note the bottom right device will bond the grounding electrode conductor to an enclosure or raceway.
Photo 2. This shows a sampling of bonding jumpers that are provided by the factory for main bonding jumpers in panels.
The scope of this article covers general requirements for grounding and bonding of electrical installations. First, we have two definitions that we need to consider in order to help us understand the principles of grounding. Effective grounded-fault current path is an intentionally constructed, low-impedance electrically conductive path designed and intended to carry current under ground-fault from the point of a ground fault on a wiring system to the electrical supply source and that facilitates the operation of the overcurrent protective device or ground-fault detectors on high impedance grounded systems. Ground-fault current path is an electrically conductive path from the point of a ground fault on a wiring system through normally non-current-carrying conductors, equipment, or the earth to the electrical supply source. Both of these are best understood as the emergency path the current takes in the event of a ground fault (which is a short from an ungrounded conductor to ground). If we have a good path, then the high current flow back to the source should operate the overcurrent device and shut down the system.
As you probably noticed, the main difference is that one is an intentionally constructed path, which is what we hope to have, and the second is any path in which the current may flow. To give a real life example of this, I remember getting a service call to a house which had smoke coming out of the walls. As luck would have it, I was very close and beat the fire department to the site. The first thing I did was shut off the main at the service and the smoke started to lessen. By the time the fire department got to the house, there was hardly any visible smoke coming out of the walls, just the smell of burning wood. The fire department broke open a hole in the wall and the plaster reinforcing wire lath had been burning its way into the wood studs, just like one of the old wood burning kits we used to have as kids. The only electrical device near this part of the dwelling was an air conditioner compressor unit. I opened the junction box of the unit and the grounding wire wasn’t connected. If it had been connected, there would have been a low impedance path that carried the current back to the breaker and caused it to open. However, one ungrounded conductor had shorted out and the only path for the fault current was through the copper refrigeration lines to the wall where they contacted the metal lath wire and energized it, causing it to heat up to the point of burning the wood framing. Without a good fault-current path back to the overcurrent device, the device just sees an additional load, but not enough to make it trip in a timely fashion.
Photo 3. The bare copper conductor here is the grounding electrode conductor that has been connected to the concrete- encased electrode (rebar) stubbed up from the building footing.
Where grounding starts
Now that we understand why we need good grounding paths, let’s start back at Part III Grounding Electrode System and Grounding Electrode Conductor, since this is where grounding starts, with a good connection made to the earth. The connections to the earth are called electrodes, and the code describes eight different types of electrodes. We will only cover the concrete-encased electrodes and ground rods, since they are the ones most commonly used in construction today. Details are found in 250.52(A)(3) for the concrete-encased electrode. This is the preferred electrode for any new construction, and it performs very well due to the fact that the concrete continues to extract moisture from its surrounding soil and has great contact with the earth simply due to its weight.
The second most common is rod or pipe electrodes, which are covered in 250.52(A)(5). Ground rods are very common and make a good connection to the earth due to the fact they are required to be 8′ in length and reach deep enough into the earth. This is the best option when adding a grounding electrode system to a facility where you can’t incorporate a concrete-encased electrode.
There are other electrodes covered in 250.52 (which you should take time to read), but I will mention one that is fading from use, and that is metal underground water pipe. For decades, it was the most common source of grounding electrode; however, with the advances made in water system products, it was found that if a facility had a metal water line that failed, it was being replaced by a non-metallic system. When that occurred, we lost our grounding electrode. Even in new housing construction, I haven’t seen a metallic water pipe feeding a residence in two decades. If you review 250.53, you will find the installation methods for each of the grounding electrodes mentioned above.
One item to note is a change made in the 2011 edition of the NEC for 250.53(A)(1) related to rod electrode installations. In the 2008 NEC 250.56, it stated that a rod, pipe or plate electrode that didn’t measure 25 ohms or less would have to be supplemented by an additional electrode. In the field, this meant an inspector had to have some assurance that one device would measure 25 ohms or less, but how do you do that? Does the inspector test it? Generally no, so it was up to the contractor to prove it met this code requirement. In practice it saved time and multiple trips to the site if the contractor simply installed two rods and then didn’t have to worry about the measurement at all. So in the 2011 NEC 250.53(A)(2), it states you will install two rod electrodes, and then there is an exception which allows one rod if you prove it meets the 25 ohms or less requirement. This is a good example of how the code is often modified to match what is actually the general practice in the field.
Photo 4. This is an example of 250.104, bonding of other systems. This is gas piping which goes throughout the house and may have the possibility of becoming energized and therefore shall be bonded.
Connecting to items to be grounded
So now that we have our actual connection to the earth, we have to connect it to those items we are trying to ground. To do this we use a conductor called the grounding electrode conductor. The grounding electrode conductor is covered in 250.62 through 250.68. First, this conductor must be made of a material resistant to any corrosive conditions to which it may be exposed. This could be various things, such as a corrosive soil, fumes within a building, or any other conditions that may damage it. Again, if we lose this connection to the electrode, we have totally lost our grounding system.
Article 250.64 is where we find the details on the installation of the grounding electrode conductor. Covered is how to secure and protect it, and depending on the size, it may need some physical protection such as a raceway. Please note that if protected by a metallic raceway, and the raceway isn’t continuous from the equipment to the grounding electrode, then the raceway must be bonded at each end to the grounding electrode, see 250.64(E). The reason for this is really pretty simple: the impedance of the conductor and the raceway are different and the current will travel at different speeds from one end to the other, so if they are not bonded and there is an air gap at one end or the other, it will arc. Repeated arcing will cause damage to the electrode conductor. It must be securely fastened to the surface on which it is carried and can be run through framing members. It shall be installed in one continuous length without a splice or joint; however, if it absolutely has to be spliced, there are four very specific ways to do it in 250.64(C). Remember this is a crucial element to the safety of the electrical system, and anytime we have a splice or connection we have created a possible failure point, so we try to avoid any conditions which may create a weak point.
Photo 5. In both of these photos, the grounding electrode conductor is the bare copper. It is being terminated on the grounded terminal location in these residential main services. Note the aluminum bussing that continues into the meter section in each of these photos to connect directly to the utility-grounded service conductor, which meets the main bonding jumper requirement.
Also please note 250.64(D), which has allowances for a single electrode and conductor to be tapped to serve several service-entrance enclosures located in close proximity to one another. Now for one of the key elements of the grounding electrode conductor — how do we size it? In Article 250.64(D)(2) we find that each electrode conductor is to be sized according to 250.66, and there we find that generally it is sized according to Table 250.66, which lists the size of the service conductors on the line side of a service and then shows us the size of the grounding electrode conductor. The sizing is based on the size of the conductors feeding the service, since we don’t have an overcurrent device on the service conductors. Refer to Table 250.66 and also review the notes, which cover the methods for multiple sets of conductors.
Now for three applications where we don’t need to use the table and that are covered in 250.66(A), (B) and (C): these deal with conditions where we have a single conductor which is the sole connection to the grounding electrode for rod, pipe, plate, concrete-encased and ground-ring electrodes. In these sections we find a new maximum size conductor requirement for each of these types of electrodes. For example, on a concrete-encased electrode you are not required to use a conductor larger than a 4 AWG copper conductor, no matter what the size of the service. I must caution you that if the design professional has designated a larger conductor, you would be obligated to follow his requirements. Remember that the code is a minimum and can always be exceeded.
Connecting to the grounded service conductor
So now that we have the electrode and the electrode conductor, what do we do with it? In 250.24 Grounding Service-Supplied Alternating-Current Systems, we find the answer. First, in 250.24(A) System Grounding Connections, we discover that the grounding electrode conductor shall be connected to the grounded service conductor. As simple as it sounds, this is one of the most critical requirements of the code. The connection can be done in various ways as outlined in 250.24, so please follow along in the code as we go.
This should be the only point where we connect together the grounded conductor, the grounding electrode conductor and the equipment grounding conductors. This is generally done at the main service disconnecting means of a service, utilizing what is called a main bonding jumper [see 250.24(B) and 250.28]. Failure to make this connection can lead to various issues, the least of which will be voltage fluctuations that may damage connected equipment.
Once we move past the service main location, we are not to connect the grounded conductor (remember this is generally referred to as a neutral) to any grounding conductors; this is covered in 250.24(A)(5). If you do, you will create parallel ground fault return paths that may not push the overcurrent device to react in a timely fashion. Or, if you are downstream of a ground fault sensor in either a GFCI or GFP device, it will cause the device to trip.
Connecting to equipment grounding conductor
From the service, the path continues in Part VI Equipment Grounding and Equipment Grounding Conductors. In 250.110 we learn that exposed, normally non-current-carrying metal parts of fixed equipment supplied by or enclosing conductors or components that are likely to become energized shall be connected to an equipment grounding conductor. In the remainder of 250.110 and in 250.112, 114 and 116, we see some specific requirements for various types of equipment. The types of equipment grounding conductors are outlined in 250.118, and the most common would naturally be a wire-type conductor. However, you will also notice within the article that various types of raceway also meet the grounding requirements. I will not go into details of any one of these specific methods, please review for yourselves.
We need to cover 250.119 Identification of Equipment Grounding Conductors, and here we find that these conductors can be bare, covered or insulated. If covered or insulated, they shall be identified with a continuous outer finish that is either green or green with one or more yellow stripes, except as permitted elsewhere in 250.119. Those exceptions make an allowance for conductors larger than 6 AWG, which normally doesn’t come in green from the factory. We are allowed to re-identify using three options: stripping the insulation or covering, coloring or marking at the termination points. Also covered in (B) and (C) are allowances for multiconductor cablesand flexible cords.
Our next concern with equipment grounding conductors is how to properly size them. In 250.122, it states that we shall size them according to Table 250.122. This table is based on the overcurrent device that is protecting the circuit. Basically, the larger the circuit ampacity size the larger the conductor that is required to handle the fault current back to the source and to cause the overcurrent device to operate. A couple of items need to be mentioned here; one is that if the ungrounded circuit conductors are increased in size for any reason, then the related equipment grounding conductor shall be proportionally increased. This might happen if voltage drop requires a larger phase conductor, since the larger conductors will have a higher fault current capacity and we have to compensate for that with a larger equipment grounding conductor.
The other item is found in 250.122(F) Conductors in Parallel, which states that in each raceway where an equipment grounding conductor is used it must be sized in accordance with the other rules in 250.122. So if you have six PVC conduits for a parallel run, you will have to install an equipment grounding conductor in each conduit, and each must be sized according to Table 250.122. However, in the body of 250.122 we find language which states that it will never have to be larger than the ungrounded conductors.
Photo 6. This is another example of bonding piping systems. On the left the water main is bonded, and in the upper left insert we have a poor example of bonding as the connection isn’t making direct contact due to the tape. On the right, I found a fire sprinkler riser at a gas station canopy and was wondering where they made the bonding connection.
Now that we have the equipment grounding conductors run where needed, what do we do with them? The purpose of the equipment grounding conductor is again to connect any normally non-current-carrying metallic parts that may become energized in order to provide what I call the emergency electrical relief system, which is needed to open the protective devices. In Part VII Methods of Equipment Grounding, you will find the details for such things as receptacles, certain boxes, ranges and dryers to name a few; again, please review these more completely on your own.
Connecting metallic items
Bonding is covered in Part V, starting at 250.90. Bonding is simply the connection of metallic items to ensure that we have a connection to the earth. Earlier we mentioned the main bonding jumper within the service, but now we are connecting other parts of the system for the purpose of ensuring electrical continuity to safely conduct any fault current that may be imposed. In 250.96, 97, and 98, we cover the most common bonding items we need to check for on our inspections.
Bonding of enclosures, raceways, cable trays and various other items (including around loosely jointed fittings) need to be addressed. One of the most common points is at factory knock-outs where we just don’t have a good ground path. So how do we size these jumpers? It depends on if you are working on the supply side of a system or on the load side. If you are on the supply side, then you use 250.66, based on the ungrounded conductor size. On the load side, we would use 250.122, which is based on the overcurrent device size. This distinction points out a very good general rule of thumb, which is that if you have an overcurrent device upstream, go to Table 250.122; if there is no overcurrent device, go to Table 250.66.
The last bonding items are in 250.104 and 106, which cover the bonding of piping systems, exposed structural steel and lightning protections systems. Review these requirements and make sure you are getting these items properly bonded in your areas. Often this is overlooked or not properly done as we sometimes tend to get casual about these items.
Connecting to separate buildings
One item which seems to be most overlooked (in housing construction especially) is 250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s). At each separate building or structure you should make sure you have a grounding electrode installed. I know this may sound bold, but let me explain. Often these types of projects start small, and you think you are going to have a single circuit, so you use the exception. Then the plan changes and now there are multiple circuits, and it is difficult to later install an electrode. In my local area, the home builders just decided to automatically install a concrete-encased electrode no matter what the original intended use of the separate structure. At times they would only intend them as a workout room, but then they could be converted to a casita (a small house) with a bathroom and cooking equipment, so it was just easier to stub up a rebar as a grounding electrode whether we needed it or not. A little planning ahead sometimes saves a lot of headaches later on.
Insuring reliable connections
The last items to cover are found in 250.8, 10 and 12. Notice that we started at the electrode and worked our way up, and these last requirements cover methods to insure good reliable grounding and bonding connections. This includes such things as the type of components to be used, even down to the types of screws. Ground clamps, which are devices for connecting conductors to various types of building materials, shall be approved for the use and may require protection, so you will have to review the listing and installation instructions on these. Through the years, probably one area of the most creative invention has been in the grounding and bonding process. There are so many products out there and electricians don’t always have access to the proper devices and therefore try to become designers, manufacturers and installers of some of the most unique methods. If it looks a little weird, ask for the literature that should have come with the components. Lastly, we must make these connections to clean surfaces, and that may require the removal of paint or other surface coating to ensure a good metal to metal connection.
This concludes the high level coverage of Article 250. I tried to do it in a logical inspection process from the bottom up, literally. Just remember to open the code book and review it with this article, and remember that grounding is the emergency safety line. Everything electrical will generally work just fine if the ground isn’t done right, but when we have some type of abnormal issue, it is the grounding installation that saves us. This is one of the most important portions of any inspection.
Read more by Randy Hunter
Posted By Ark Tsisserev,
Wednesday, May 01, 2013
Updated: Friday, April 26, 2013
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Apparently, there is some confusion on this subject. Let’s tackle it step-by-step.
Consumer’s service, a feeder and a branch circuit are defined by the Canadian Electrical Code as follows:
"Service, consumer’s — all that portion of the consumer’s installation from the service box or its equivalent upto and including the point at which the supply authority makes connection.
Feeder — any portion of an electrical circuit between the service box or other source of supply and the branchcircuit overcurrent devices.
Branch circuit — that portion of the wiring installation between the final overcurrent device protecting the circuit and the outlet(s)."
Although each of these defined portions of an electrical installation has a different purpose, Rule 8-104 of the CE Code offers absolutely similar fundamental requirements for a selection of a minimum rating of a consumer’s service, feeder or branch circuit.
This Rule also describes ampere rating as follows:
"8-104(1) The ampere rating of a consumer’s service, feeder, or branch circuit shall be the ampere rating of the overcurrent device protecting the circuitor the ampacity of the conductors, whichever is less.”
It means that if the selected ampacity of conductors (based on a particular ampacity table) is, for example, 225 A but the selected rating of the overcurrent device is 200 A, then the ampere rating of such circuit (feeder or consumer’s service) is 200 A.
So far, so good. But what are the main criteria for selecting a rating of a circuit at a specific value? What is the most important reference point? Similarly to a selection of the shoe size, which should be based on the size of the feet (if we want some level of performance and safety), selection of a circuit rating should be based on the calculated load.
Rule 8-104 provides following clarity on this condition as well:
"8-104(2) The calculated load in a circuit shall not exceed the ampere rating of the circuit.”
It means that under no condition selected conductors of a circuit should have ampacity value less than the calculated load, or under no condition the selected O/C device protecting conductors of that circuit should have a rating or setting at the value less than the calculated load in the circuit.
This Rule also provides criteria for determination of whether a calculated load should be considered continuous or not.
"8-104(3) The calculated load in a consumer’s service, feeder, or branch circuit shall be considered a continuous load unless it can be shown that innormal operation it will not persist for
(a) a total of more than 1 h in any two-hour period if the load does not exceed 225 A; or
(b) a total of more than 3 h in any six-hour period if the load exceeds 225 A.”
Therefore, only if it could be demonstrated that a load does not persist for more than half of the time period described in a condition (a) or (b) above, such calculated load is permitted by the Code to be considered as non-continuous load.
In fact, the CE Code only considers total load as non-continuous when such load is calculated for a purpose of selecting service conductors for a single dwelling or service/feeder conductors for a dwelling unit in an apartment building. All other loads are considered by the Code to be continuous, and appropriate demand factors should be applied to those continuous loads.
Although Rule 8-104(2) mandates a general criteria for selection of a circuit rating (i.e., that the calculated load in a circuit cannot exceed ampere rating of that circuit), this general criteria is additionally supplemented by Subrules 8-104(4) and 8-104(5), and the Code users should clearly understand which particular Subrule should applyin each specific case.
Subrule 8-104(4) states the following:
"8-104(4) Where a fused switch or circuit breaker is marked for continuous operation at 100% of the ampere rating of its overcurrent devices, thecontinuous load as determined from the calculated load shall not exceed
(a) 100% of the rating of the circuit where the ampacity of the conductors is based on Column 2, 3, or 4 of Table 2 or 4; or
(b) 85% of the rating ofthe circuit where the ampacity of the conductors is based on Column 2, 3, or 4 of Table 1 or 3.”
This means that if a fused switch or a circuit breakerspecifically marked for continuous operation at 100% ampere rating of its O/C device is selected for the installation, then the size of conductors indicated in Tables 2 or 4 could be selected for that calculated loadbased on criteria outlined in Subrule 8-104(2) shown above,(i.e.,provided that the continuous load does not exceed the selected ampacity of the circuit conductors). This also means that if free air conductors are intended to be selected for such installation in accordance with Table 1or 3, then the continuous load under no condition is allowed to exceed 85% of the selected ampacity of conductors.
When a traditional (80% rated, readily available off the shelf) fused switch or a circuit breaker is specified for installation in a circuit, then provisions of Rule 8-104(5) must apply as follows:
"8-104(5) Where a fused switch or circuit breaker is marked for continuous operation at 80% of the ampere rating of its overcurrent devices, thecontinuous load as determined from the calculated load shall not exceed
(a) 80% of the rating of the circuit where the ampacity of the conductors is based on Column 2, 3, or 4 of Table 2 or 4; or
(b) 70% of the rating of the circuit where the ampacity of the conductors is based on Column 2, 3, or 4 of Table 1 or 3.”
In this case, the continuous calculated load under no condition is allowed to exceed 80% of the selected ampacity of conductors, if Table 2 or Table 4 is used (i.e., when a multi-conductor cable, or conductors in raceways are intended to be installed), or the continuous calculated load under no condition is allowed to exceed 70% of the selected ampacity of conductors – if Table 1 or 3 is used.
Subrule 8-104(6) warns the Code users of additional conditions that may exist in installation (i.e., high ambient temperature or more than 3 conductors are installed in a raceway), andthat in these cases specific derating factors must be applied.
"8-104(6) If other derating factors are applied to reduce the conductor ampacity, the conductor size shall be the greater of that so determined or thatdetermined by Subrule (4) or (5).”
So, based on the discussion above, the following conclusions could be made:
1. Rating of the circuit overcurrent devices and ampacity of the circuit conductors shall not have values smaller than the calculated load of that circuit; and
2. If the calculated load in the circuit is continuous, this load cannot exceed 70%, or 80% or 85% of the rating of that circuit, depending on the applicable requirements of Rule 8-104(4) or 8-104(5).
But what about a correlation between the ampacity of circuit conductors and the overcurrent devices protecting these conductors? Does any requirement exist in the Code for such correlation?
Theanswer to this question could found in Rule 14-104(1) of the Code as follows:
"14-104 Rating of overcurrent devices
(1) The rating or setting of overcurrent devices shall not exceed the allowable ampacity of the conductors that they protect, except
(a) where a fuse or circuit breaker having a rating or setting of the same value as the ampacity of the conductor is not available, the ratings or settings given in Table 13 shall be permitted to be used within the maximum value of 600 A;
(b) in the case of equipment wire, flexible cord in sizes Nos. 16, 18, and 20 AWG copper, and tinsel cord, which are considered protected by 15 A overcurrent devices; or
(c) as provided for by other Rules of this Code.”
This requirement indicates to the Code users that in general (except as it may be permitted in other Rules of the Code), the rating or setting of the circuit overcurrent devices are not allowed to exceed ampacity of the circuit conductors protected by such overcurrent devices. This Rule also advises the Code users that such general correlation requirementmay be disregarded under provisions of Table 13, but only in those situations where the standard rating or setting of the overcurrent device of the same (or smaller) value than the ampacity of the selected conductors is not available.
Let’s illustrate the above requirements of Rule 8-104 and Rule 14-104 by a couple of examples.
Example 1:A calculated load of a stand-alone building occupied by a restaurant is 300 A at 120/208 V. The power to the building is supplied by a buried 4 conductorcopper armoured cable installed by an electrical contractorfrom the utility PMTto the electrical service boxcontaining a standard 80% rated circuit breaker. The circuit breaker is marked for the maximum allowable termination temperature at 75 Deg. C.
In this case, Rule 8-104(5(a) would have to apply for selection of the ampacity of the service conductors. Based on the calculated load of 300 A the next standard value of the conductors ampacity should be selected fromthe 75 Deg. C column of Table 2, and this value should be equal or more to the result of multiplication of 300 A by 1.25, which is 375 A. From Table 2, the next standard conductor ampacity meeting this requirementis 380 A, and this ampacity will allow us to select a cable sized at 500 MCM. This ampacity (and this cable size) will workfor the intended continuouscalculated load if there are no additional needs to de-rate the assigned ampacity (i.e., due to the voltage drop or high ambient temperature requirements).
Now, we can select the trip setting of the service circuit breaker based on the provision of Rule 8-104(5)(a). As the trip setting cannot be less than 375 A, then the next standard setting allowed by Rule 14-104(1) should be 400 A, provided that such setting meets the criteria mandated by Table 13. Review of Table 13 will allow the Code users to ascertain that the conductors with ampacity values from 351 A to 400 A could be protected by the overcurrent device set or rated at 400 A. Thus, a circuit breaker with a 400 A frame and 400 A trip set will work in this case.
Therefore, the rating of the serviceis selected successfully for the continuous load of the restaurant in our example 1.
Example 2: A calculated load of a single dwelling (of a detached two storey house) is 178 A. An electrical contractor has lots of 4/0 aluminum 3 conductor armoured cable in stock and wants to use it as the consumer’s service conductors, to supply the loads of the house.
As the load of a single dwelling is not considered to be continuous for the purpose of selection of the ampacity of service conductors supplying the singledwelling [see Rule 8-200(3) of the CE Code], the ampacity of conductors selected from 75 Deg. C column of Table 4 should not be smaller than the calculated load of 178 A. 4/0 aluminum cable intended to be used by the contractor will do the trick, as the ampacity of this cable is 180 A. This means that the condition of Rule 8-104(2) is met. What about the selection of the service overcurrent device? Can thecontractorinstall a 225 A combination panelboard with the circuit breaker trip set at 200 A? Table 13 will allow such setting, as a 200 A overcurrent device will be able to protect conductors with ampacities between 176 A and 200 A.
This means that the rating of this service is also adequately selected for the non-continuous load of the single dwelling.
Let’s spend a few moments of interesting relaxation allowed by Rule 14-104, as shown below:
"14-104 Rating of overcurrent devices
The rating or setting of overcurrent devices shall not exceed the allowable ampacity of the conductors that they protect, except.......
(c) as provided for by other Rules of this Code.”
This relaxation is intended for specific needs to correlate the overcurrent devices with ampacities of conductors for such loads as motors and capacitors where inrush currents (in case of motors) or charging currents (in case of capacitors) could be quite large, and the O/C devices should be selected so as to allow a successful start of this type of connected loads.
Relaxation allowed by Rule 62-116(7) for the correlation between the overcurrent protection of the service, feeder or branch circuit conductors and the ampacity of these conductors is another example of such provision of Rule 14-104(c).
It appears that the fundamentals of the circuit loading have been sufficiently addressed.
But what about an additionalrelaxation allowed by Rule 8-106(1) shown below:
"8-106 Use of demand factors
(1) The size of conductors and switches computed in accordance with this Section shall be the minimum used except that, if the next smaller standard size in common use has an ampacity not more than 5% less than this minimum, the smaller size conductor shall be permitted.”
This relaxation creates lots of confusion to the Code users, as itflagrantly conflicts with fundamental requirements of Rule 8-104 (it should be noted that Rule 8-104 has no notwithstanding provisions for such relaxation). In addition, use of this relaxation could reduce electrical safety, as it may lead to a selection of the conductors with ampacities smaller than the connected load. A case in point is when the load is not determined by a calculation but bymeasuring a demand in accordance with Rule 8-106(8) of the Code.
Despite the fact that this relaxation exists in the Code, there are many electrical safety regulators who are reluctant to accept use of this relaxation for the reasons expressed above.
It should be noted that the proposal has been submitted to Section 8 S/C to delete this 5% relaxation permission from Rule 8-106 and to introduce it as a notwithstanding Clause to Rules 8-104(4) and 8-104(5)under a control of a special permission by the AHJ.
Thus, as usual, when any specific issues arise in respect to load calculations, the authorities having jurisdiction should be consulted by the designers and contractors.
Read more by Ark Tsisserev
Posted By Thomas A. Domitrovich,
Wednesday, May 01, 2013
Updated: Friday, April 26, 2013
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Arc flash has and continues to be an issue for our industry. All you need to do is speak with someone who has survived an arc flash event or look at the statistics to understand the magnitude of impact these events have on not only that person who may have survived but also on everyone else either directly or indirectly involved; at work and at home. This is a problem in our industry that happens all too often but I firmly believe that these events can and should be things of the past. We have the technology and work practice knowledge to take a bite out of the statistics of arc flash, and NEC 2014 is making great strides in the right direction.
Surprisingly, after a search for a definition of the term arc flash, I could not find a formal definition in IEEE, NFPA or other similar publications. These documents define arc flash boundary, arc flash incident energy, arc flash hazard and other similar terms but not arc flash. So I am taking a liberty here to provide a definition that I have put together based on reading many different documents relating to arc flash and arc flash energy. "An arc flash is the light, heat, sound and gases produced as a result of a rapid release of energy due to an arcing fault sustained by the establishment of highly conductive plasma.” The severity of the event is not in the definition above as that aspect of an arc flash event is addressed by some of the other definitions above which address boundaries and incident energy.
Figure 1. Arc Flash Statistics
Arc flash incidents occur all too often and impact many lives; the remnants of the event may last forever. Figure 1 is a small peek into the problem. It illustrates statistics around a survey of 120,000 workers. These events can be violent, yielding temperatures as high as 20,000°C and forces in excess of 100kPa (Kilopascal). In addition to temperatures and pressures, there may be flying debris that also can do an extensive amount of damage.
The plasma mentioned in our definition of arc flash, amongst other things, introduces impedances that work to reduce the three phase fault current to a lower value of arcing current: "A fault current flowing through electrical arc plasma, also called arc-fault current and arc current.” 1
Figure 2. Breaker response time for a bolted fault current. Note the very fast clearing time removes the fault reducing arc-flash energy.
Figure 3. Breaker response time for an arcing fault current which is of a magnitude less than the calculated bolted fault current. Notice you are in the overload region of the trip curve and your clearing times are much longer resulting in a lot more energy.
Arcing current can be significantly lower than the calculated three-phase bolted fault. This lower value may be lower than the instantaneous pickup of the overcurrent protective device which would mean that the arcing current could be permitted to flow for a long period of time. To illustrate this, figures 2 and 3 include the time current characteristic (TCC) curve of a standard thermal magnetic circuit breaker. Figure 2 shows a calculated bolted fault value that falls above the instantaneous pickup and in the instantaneous region of the overcurrent protective device. Figure 3 illustrates that the arcing current is a percentage of the bolted fault current that in this case falls below the instantaneous pickup of the overcurrent protective device.
This response time results in an arcing current that is permitted to flow from approximately 0.5 second to 3 seconds which happens to be a very long time when you consider energy is time multiplied by the square of current. This illustrates why an arcing current downstream of an overcurrent protective device can do a lot of damage before a device trips. For an example such as that shown in Figure 2, some other means would have to be put in place to address the arcing fault and clear it in a shorter amount of time.
Arc flash events can be caused by metallic tools, test probes, loose equipment parts, or similar items coming in contact with energized bare parts creating a short circuit. Other sources have been known to include the misapplication of test instruments as test instruments applied beyond their listing. To address the problem in the industry we turn to codes and standards. A peek into the activity in this area illustrates the type of attention arc flash is getting by the electrical industry.
Electrical Codes / Standards
When I think about arc flash and codes and standards, two key documents come to mind; NFPA 70 National Electrical Codeand NPFA 70E Standard for Electrical Safety in the Workplace. These documents work together to help reduce the incidents of arc flash, in addition to many other hazards.
The key thing that separates these two documents is how they are enforced. NFPA 70 is familiar to many, enforced by electrical inspectors across the country, used as an installation requirement by many electrical contractors across the country and in the design process by many professional engineers across the country. It is an installation requirement that is adhered to and enforced at the early stages of the development of a structure. This document includes such requirements as GFCI, AFCI, equipment ground fault and grounding/equipment bonding which all act to prevent a problem from occurring or work to mitigate the effects of events should they occur. The systems installed per the NEC are later maintained by many in the industry.
NFPA 70E, on the other hand, is not enforced in the same manner. This document is primarily enforced by OSHA and usually after an event occurs. Recently though, OSHA has been enforcing workplace safety practices during routine inspections. In my mind, when it comes to stopping the problem before it occurs, NFPA 70 is the document that has the most impact.
With respect to arc flash, the NEC has not historically been very active until just recently. Section 110.16, Arc-Flash Hazard Warning, was the first introduction of the term arc-flash to the NEC. It was introduced in the 2002 version of the Code and is a requirement for a sign that raises awareness of the hazard. Signs are great ways to raise awareness of hazards but implementing technologies that act to mitigate the problem is a more direct way to address the issue.
NEC 2012 took a more direct approach in the fight against arc flash. This document introduced a new section 240.87, Noninstantaneous Trip, intended to specifically target the arc flash issue. Controversial as any other big change, this new section came in with one proposal (Proposal 10-82) and many comments (Comments 10-36, 10-37, 10-38, 10-39, 10-40, 10-41, 10-42, 10-43, and 10-44). Figure 5 illustrates the language that was decided upon for 240.87 and which can be found in NEC2011. This language was met with many questions. For example, the phrase "utilized without an instantaneous” came under fire by some in the industry as it was debated whether or not simply having instantaneous trip capabilities on the breaker, even when turned off, was enough to meet the intent of the code. But as with many sections of the NEC, time will help this section get better.
The 2014 cycle of the NEC offered another opportunity for public input. The Proposal phase of NEC 2014 saw 7 proposals on section 240.87 of the Code (10-53a, 10-54, 10-55, 10-56, 10-57, 10-58, and 10-59). The Comment phase brought out 10 comments (10-20, 10-21, 10-22, 10-23, 10-24, 10-25, 10-26, 10-27, 10-28, and 10-29). The panel settled on a language that is not only crystal clear for the inspector but will also have a considerable impact on the arc flash problem. The 2014 language, as gathered from ROP and ROC documents, is shown in figure 6. Note that the final published version of the NEC may have some minor changes but this should get you in the ballpark. The new language has removed any ambiguity of where this section applies. I will add that the technologies outlined in this section can be applied below 1200 amps as well.
The code panel utilized language from section 230.95 of the NEC when creating what we will soon see as the new Section 240.87. Section 230.95 states ". . . The rating of the service disconnect shall be considered to be the rating of the largest fuse that can be installed or the highest continuous current trip setting for which the actual overcurrent device installed in a circuit breaker is rated or can be adjusted.” With minor modifications, this language served the panel well in that the language is familiar to the inspector and installer. Good code is clear, concise and familiar. This new section is just that.
Arc Reduction Technologies
There are four technologies included in this section plus a provision that permits the application of an approved equivalent. Let’s talk briefly about each of these technologies and we’ll focus a little more on the approved equivalent later.
Figure 4. Section 110.16
Zone Selective Interlocking (ZSI)
A circuit breaker equipped with zone selective interlocking provides a method to reduce fault clearing times should a fault occur while working on energized circuits within the zone of protection (between the upstream and downstream pair of circuit breakers). The reduced clearing times greatly reduce arc flash energy.
Zone selective interlocking utilizes a communication signal between two or more trip units applied on upstream and downstream pairs of breakers that have already been selectively coordinated. During fault conditions, each trip unit that senses the fault sends a restraining signal to all upstream trip units. When the upstream trip unit sees this restraining signal, it will remain closed while the downstream breaker clears the fault. In the absence of a restraining signal, when the fault is between the two trip units, the upstream trip unit ignores its programmed settings and trips with no intentional time delay, reducing the clearing time, minimizing damage at the fault point and reducing the arc flash energy.
Differential relaying is very similar to zone selective interlocking in that it is able to determine if a fault occurs within a particular zone of protection, reduces the clearing time, minimizes damage at the fault point and reduces the arc flash energy. It is different in that it monitors the amount of current going into and out of a zone of protection. If the amount of current going into the zone is greater than the amount of current flowing out of the zone, then the device knows that the fault is within the zone and acts to open the circuit with no intentional delay. If the current going into the zone and the current going out of the zone are equal there is no fault within the zone, so the circuit breaker does not trip.
Energy Reducing Maintenance Switch
A circuit breaker equipped with an arc flash reduction maintenance system provides a simple and reliable method to reduce fault clearing times should a fault occur while working on energized circuits downstream. The reduced clearing times greatly reduce arc flash energy.
An arc reduction maintenance system can be turned on and off automatically or manually to reduce arc flash energy. In the "on” position, it reduces the clearing time of a circuit breaker that has been intentionally delayed for selective coordination purposes. In the "off” position the system responds in the manner in which it has been programmed to meet selective coordination requirements.
This technology is based on the realization that when working on energized electrical equipment, a fault that occurs within that gear needs to be cleared as quickly as possible. While this seems obvious, in actual installations, intentional delays are included in upstream devices to ensure selective coordination with downstream devices. This means that if a fault were to occur inside the equipment, the downstream breaker might never clear the fault regardless of how much delay is or isn’t programmed in the upstream breaker. This maintenance switch technology permits removing this delay while energized work is being conducted.
Figure 5. NEC-2011 language for Section 240-87, Noninstantaneous Trip
Energy Reducing Active Arc-Flash Mitigation Systems
A circuit breaker equipped with an energy reducing active arc-flash mitigation system provides a simple and reliable method to reduce fault clearing times. Work locations downstream of a circuit breaker with this technology can have a significantly lower incident energy level. When activated, this system monitors system parameters and acts to identify an arc flash. If an arc flash event occurs, the arc is diverted via various types of technology while opening an upstream circuit breaker, eliminating the faulted condition and de-energizing the system.
Approved Equivalent Means
Section 90.4 of the NEC has a provision for the authority having jurisdiction for enforcing the Code, to permit alternative methods to a requirement where it is assured that equivalent objectives can be achieved by establishing and maintaining effective safety. The phrase "or equivalent” is used 77 times in NEC 2011 with some instances being much more clear cut than others. The phrases "approved equivalent means” and "or equivalent” can be quite controversial in some instances when the inspector is being presented with a design that doesn’t meet the letter of the code but is being asked to be considered as equivalent. Inspectors across the country probably have those top two or three examples that they see all the time and have their dialog down pat when presented with the "equivalent” design. Section 240.87 offers another example of this but the answer can be quite clear.
Figure 6. NEC 2014 Section 240.87
Before an inspector evaluates a proposed equivalent means, we must first understand the intent of this section of the Code. The new title change helps considerably with this as it clearly states that it is there for "Arc Energy Reduction.” The inspector can make his/her job very transparent when approving an equivalent means. The first step is to request the results of an arc flash study for one of the four listed options and the results of an arc flash study with the proposed equivalent means. This yields two arc flash numbers that can be compared. The proposed equivalent means shall be considered "approved” when the arc flash value for the proposed equivalent means is equal to or less than the arc flash value calculated for one of the four listed technologies.
The inspector does not have to perform a calculation, read a TCC curve or any of the literature for a breaker or other type of system being offered as an equivalent means. Keep it simple. Ask for two arc flash values as described above and compare the numbers. It’s that simple.
NEC 2014 Section 240.87 is a historical code change and one of the most important leaps in arc flash safety for the electrical industry. This new language, through my eyes, will take a bite out of the arc flash issue and save lives. As we come closer to the annual meeting in Chicago for the final stages of NEC 2014, stay tuned for the final agreed upon language. Together we can make a difference.
As always, keep safety at the top of your list and ensure you and those around you live to see another day.
1IEEE Std. 1584-2002 "IEEE Guide for Performing Arc-Flash Hazard Calculations”
Read more by Thomas A. Domitrovich
Safety in Our States
Posted By Jesse Abercrombie,
Wednesday, May 01, 2013
Updated: Friday, April 26, 2013
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Have you recently received a pension buyout offer? If so, you need to decide if you should take the buyout, which could provide you with a potentially large lump sum, or continue accepting your regular pension payments for the rest of your life. It’s a big decision.
Clearly, there’s no "one size fits all” answer — your choice needs to be based on your individual circumstances. So, as you weigh your options,you’ll need to consider a variety of key issues, including the following:
Estate considerations — Your pension payments generally end when you and/or your spouse dies, which means your children will get none of the money. But if you were to roll the lump sum into an Individual Retirement Account (IRA), and youdon’t exhaust it in your lifetime, you could still have something to leave to your family members.
Taxes — If you take the lump sum and roll the funds into your IRA, you control how muchyou’ll be taxed and when, based on the amounts you choose to withdraw and the date you begin taking withdrawals. (Keep in mind, though, that you must start taking a designated minimum amount of withdrawals from a traditional IRA when you reach age 70½. Withdrawals taken before age 59½ are subject to taxes and penalties.) But if you take a pension, you may have less control over your income taxes, which will be based on your monthly payments.
Inflation — You could easily spend two or three decades in retirement, and during that time, inflation can really add up. To cite just one example, the average cost of a new car was $7,983 in 1982; 30 years later, that figure is $30,748, according to TrueCar.com. If your pension checksaren’t indexed for inflation, they will lose purchasing power over time. If you rolled over your lump sum into an IRA, however, you could put the money into investments offering growth potential, keeping in mind, of course, that there are no guarantees.
Cash flow— Ifyou’re already receiving a monthly pension, andyou’re spending every dollar you receive just to meet your living expenses, you may be better off by keeping your pension payments intact. If you took the lump sum and converted it into an IRA, you can withdraw whatever amount you want (as long as you meet the required minimum distributions), butyou’ll have to avoid withdrawing so much thatyou’ll eventually run out of money.
Confidence in future pension payments — From time to time, companies are forced to reduce their pension obligations due to unforeseen circumstances. You may want to take this into account as you decide whether to continue taking your monthly pension payments, but it’s an issue over which you have no control. On the other hand, once your lump sum is in an IRA, you have control over both the quality and diversification of your investment dollars. However, the trade-off is that investing is subject to various risks, including loss of principal.
Before selecting either the lump sum or the monthly pension payments, weigh all the factors carefully to make sure your decision fits into your overall financial strategy. With a choice of this importance, you will probably want to consult with your financial and tax advisors. Ultimately, you may find that this type of offer presents you with a great opportunity — so take the time to consider your options.
Read more by Jesse Abercrombie
Posted By Steve Foran,
Wednesday, May 01, 2013
Updated: Friday, April 26, 2013
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In the early 90s, utilities were in the midst of
massive change as downsizing, right-sizing—or whatever you called it — swept
the continent. Driven by technology, fewer people were needed to get the same
work done and from this emerged an industry called Process Re-engineering.
Our utility was engulfed in change. Our new business
processes resulted in many changes in responsibilities for many people, but one
affected our department very significantly. At the time we were responsible for
technical training associated with revenue metering.
The proposed change would reduce both travel and the
number of people needed to deliver metering services to residential customers
by combining two separate job functions together into a single job. I cannot recall
the exact numbers, but for illustrative purposes it was projected that we could
combine the work of 15 meter installers and 95 meter readers into, say, 100
multi-disciplined metering workers, resulting in a net reduction of 10 people.
The challenge was that the technical competence
required in the newly created position was higher than that of the 95 meter
To safely perform their duties, meter installers must
understand the meter nameplate, know how to identify the proper device for a
service and be competent to work around energized equipment. Quite simply, the
meter readers were not competent to do this work.
A comprehensive training program was developed and
delivered. It covered many aspects of the residential service which included
both theoretical and practical components where employees had to demonstrate
From the training, participants learned about the
risks associated with metering and energized equipment. Most importantly, they
obtained the knowledge and skills needed to safely manage the risks.
Of the many risks at the electrical service entrance,
there is one that stands out above all others. This risk came as a surprise to
every single participant in our training. In fact, none of the meter readers
were aware that this risk even existed.
Most meter readers thought the greatest risk was
electrical shock. Contact with 120 V is a risk; however, a far greater risk is
the fault level available at the service entrance in the event of a ground
fault. The potential physical harm to people and property as a result of a
short circuit in a meter base can be catastrophic.
For our system, we calculated the maximum possible
fault level at a 200 A 120/240 Volt service (close to a large substation, short
service run, large distribution transformer, etc.). Here’s what we found: the power delivered in the event of a short
circuit (even though only momentarily) is comparable to the power delivered by
a typical jet engine that you see on the wings of a large airplane.
In our training, we explained this to our
participants and asked them, "Would you stick a screw driver into a jet engine
while it’s running? What kind of
precautions would you take around a jet engine?”
A fault at a meter
base has the ability to instantaneously produce the same power delivered by a
jet engine. But unlike the jet engine, which makes all kinds of noise and
produces so much wind that you wouldn’t dare get too close, a meter base just
sits there — you can’t even tell if it is energized by looking at it.
Trainees told us that their biggest take-away was
their newfound appreciation of something which they were previously unaware.
As for me, I learned that we must be open to looking
at situations in new ways so we can see what was once invisible. Secondly, use
appreciation (appreciation of the risk, work methods, design, etc.) to replace
feelings of fear and lack of understanding.
The new service model was safely
implemented and I hear from colleagues who still work at the utility that they
continue to re-engineer their metering and customer services processes.
Posted By Steve Douglas,
Wednesday, May 01, 2013
Updated: Friday, April 26, 2013
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Residential load calculations first appeared in
the Canadian Electrical Code Part I (CE Code) in
the second edition dated 1930. In the 1930 edition, the load calculation rules
were in Section 6 Conductors. The calculations were quite different from the
present day calculations. For residential installations, the calculations were
based on the number of branch circuits being installed instead of the dwelling
floor area. In the fourth edition, dated 1939, a demand factor table for
lighting load based on the floor area was added. In the sixth edition dated
1953, the Conductor Section including the load calculation requirements were
moved to Section 4 Conductors. This calculation format remained until the
seventh edition, dated 1958. A new section called Circuit Loading and Demand
Factors including the single dwelling load calculations was added as Section 8
to the eighth edition of the CE Code dated 1962.
Photo 1. Single dwelling units as defined in the CE Code Part I
In the 1958 edition, calculations were similar to the
calculations of today with the main difference in the calculations being the
basic load. The basic load covering lighting and convenience outlets was 3,500
W for a residence with a living area up to 500 ft² (46.5 m²). For a residence
with a living area over 500 ft² and up to 1500 ft² (139.4 m²), the basic load
was 4,500 W with an additional 1000 W for each 1000 ft² (93m²) or portion
thereof. The 1958 basic load requirements stayed the same until the twelfth
edition dated 1975 when the basic load was increased to the requirements of the
Rule 8-200 of the 2012 CE Code covers load
calculations used to determine the minimum feeder or service size for
single dwelling units. To start off, we should establish what a dwelling unit
is. Section 0 defines a single dwelling unit as "a dwelling unit
consisting of a detached house, one unit of row housing, or one unit of a
semi-detached, duplex, triplex, or quadruplex house,” and a dwelling unit
as "one or more rooms for the use of one or more persons as a
housekeeping unit with cooking, eating, living, and sleeping facilities.”
Subrule (1) of Rule 8-200 is divided into two items (a) and (b). Item (a)
details the specific criteria for calculations and Item (b) mandates the
absolute minimum allowable ampacity of the service or feeder size – based on
the floor area. 100 A is required by the Code where the floor area of the
single dwelling, exclusive of basement floor area, is 80 m² (861 ft²) or more,
and 60 A is the minimum permitted service/feeder ampacity – where the floor area
of the single dwelling, exclusive of basement floor area, is less than 80 m².
Item (a) is further divided into seven items (i) to (vii).
Items (i) and
(ii) detail a basic load for the dwelling unit. This basic load includes 120 V 15- and 20-amp
convenience outlets, lighting loads and motor loads rated up to 1500 W. The
basic load for the dwelling unit is 5000 W for the first 90 m² (968 ft²) of
living area plus an additional 1000 W for each 90 m² or portion thereof in
excess of 90 m². The living area is determined as 100% of the ground floor,
100% of any area used for living purposes on the upper floor, plus 75% of the
basement area of the dwelling unit.
The next step in Item (iii) is to add the electric
space-heating and air-conditioning loads. Where it is known that the
installed electric space-heating and air-conditioning loads will not be used
simultaneously, the larger of the electric space-heating load or the
air-conditioning load is added to the base load. For electric space-heating
systems consisting of electric thermal storage heating, duct heater, or an
electric furnace, the connected heating load is calculated at 100% of the
equipment ratings. Where the electric heating installation is provided with
automatic thermostatic control devices in each room or heated area, the
electric space-heating load is 100% of the first 10 kW of connected heating
load plus the balance of the connected heating load at a demand factor of 75%.
Photo 2. A 11 kW electric range used in the article example
The next loads to add are any electric ranges.
Item (iv) allows 6000 W for a single range to be added to the basic load
provided the range does not have a rating in excess of 12 kW. In the event the
electric range is rated more than 12kW, 40% of any amount exceeding 12 kW will
need to be added as well.
Now we add water heaters. Item (v) indicates
any electric tankless water heaters or electric water heaters for steamers,
swimming pools, hot tubs, or spas are added to the basic load at 100% of
Item (vi) is new for the 2012 CE Code and
requires that any electric vehicle charging equipment loads also be added to
the basic load at 100% of equipment ratings.
The final step in Item (vii) is to add any
additional loads at 25% of the rating of each load with a rating in excess
of 1500 W if an electric range has been provided for, or 100% of the rating of
each load with a rating in excess of 1500 W up to a total of 6000 W plus 25% of
the load in excess of 6000 W if an electric range has not been provided for.
Photo 3. The nameplate of a 1500 W microwave oven
Photo 4. A 1500 W microwave oven used in the article example
As an example we will look at a 269 m² (2900 square
foot) residence with the following loads:
- lighting load
- 4 small appliance branch circuits
- laundry circuit 1500 W
- natural gas heating
- air conditioner 6000 VA
- electric range 11,000 W
- hot tub 8000 W (2 hp motor)
- Level II electric vehicle charger 7200 W
- electric dryer 5000 W
- garbage disposal 800 W
- microwave 1500 W
- dishwasher 1200 W
- electric water heater 4500 W
The calculated load for the 2900 ft² (269 m²)
single dwelling in this example is 173.1 amps.
The basic load is calculated based on the floor area
of the single dwelling. The load for the first 90 m² is 5000 W, leaving 179
m² of floor area. The next 90 m² has a load of 1000 W, and an additional
1000 W for the remaining 89 m². The total basic load of 7000 W includes the
lighting, convenience receptacles, small appliance branch circuits, laundry
circuit, garbage disposal, and the dishwasher.
The heating of the single dwelling is a gas furnace
and no electric heat is installed, leaving the 6000 W air-conditioning load
added with a demand factor of 100%.
The electric range for this single dwelling is less
than 12 kW providing a load for the calculation of 6000 W.
The 8000 W hot tub and the 7200 W electric vehicle
charging equipment are now added with a demand factor of 100%.
Any additional loads with a rating in excess of 1500
W are now added with a demand factor of 25%. In this example, the additional
loads over 1500 W are the 5000 W dryer and the 4500 W storage type water
heater; 25% of the 9500 W gives us 2375 W to be added to the calculation.
Table 1. Summary of the single dwelling service load calculation
Now that we know the calculated load, we can
determine the minimum service and conductor size. The ampacity of the load is
173.1 amps (41550 / 240 = 173.1). In most installations, the continuous load on
a service is limited to the continuous load rating of the equipment being used.
Subrule (3) of Rule 8-104 considers all loads continuous unless it can be shown
that in normal operation the load will not persist for a total of more than one
hour in any two-hour period for loads not exceeding 225 amp, or a total of more
than three hours in any six-hour period for loads in excess of 225 amp. In the
case of single dwelling units Subrule (2) of Rule 8-200 allows these loads to
be considered as a non-continuous load for application of Rule 8-104. However,
although Section 86 considers the EV charging equipment to be a continuous
load, when this load is calculated for the purpose of defining the ampacity of
a service in a single dwelling, such EV charging equipment load is not
considered as continuous load, similarly to all other loads under this Rule.
This means 100% of the calculated load for a single dwelling can be used to
determine the service equipment ampere rating. For our 269 m² example a
standard rating of 175 amp overcurrent device could be selected in the service
box as the calculated load is 173.1 amp. Typically 175 amp rating of the
overcurrent device will necessitate installation of the 200 A rated service
box, as 175 A rating for the service fused disconnect or the service circuit
breaker for residential installations is not available. In most cases a 200-amp
service would be installed with a 175-A or 200-A trip setting or rating. Let’s
consider that the trip setting of the service overcurrent device was selected
at 200 A.
The size of the service conductors are now
established using Rules 4-004, 4-006, and 14-104. As all distribution equipment
presently available has a temperature limitation of 75⁰C, Rule 4-006 requires
the allowable ampacity to be based on the 75⁰C column of either Table 2 or 4
for conductors installed in a raceway. The smallest 75⁰C conductor allowable
ampacity from Tables 2 and 4 for the calculated load of 173.1 amp are 2/0
copper with an allowable ampacity of 175 amp, or 4/0 aluminum with an allowable
ampacity of 180 amp.
Photo 5. The nameplate for a 1200 W dishwasher used in the article example
The next step is to verify the conductor selected meets
the requirements of Rule 14-104. Rule 14-104 requires the overcurrent device to
have a setting not higher than the allowable ampacity of the conductors being
protected. Where the conductor allowable ampacity does not correspond with the
overcurrent protection commercially available, Table 13 provides details on
acceptable limits for over protection settings. Based on the fact that a
200-amp service will be installed with a main 200-amp trip setting for the
breaker, Table 13 limits the conductor allowable ampacity to be not less than
176 amps. In the case of the copper conductors, the 2/0 copper conductor with
the allowable ampacity of 175 amp is undersized. At this point some code users
will try to apply "the 5% rule” in Subrule (1) of Rule 8-106 to the 175
allowable ampacity of Table 2. Subrule (1) of Rule 8-106 allows loads
calculated in accordance with Section 8 to be within 5% of the allowable
ampacity of the conductors selected. This means the 5% allowance can be applied
to a calculated load. Applying the "5% rule to a conductor allowable ampacity
table is a misapplication of Subrule (1).
In summary, the minimum
conductor size allowed for the 200-amp service where the conductors are
installed in a raceway for the example in this article is either 3/0 copper or
4/0 aluminum. If the main breaker of this service was reduced to 175 amp the
minimum copper conductor size could be reduced either 2/0, and the aluminum conductor
would remain at 4/0.
Posted By David Clements,
Friday, March 01, 2013
Updated: Wednesday, February 13, 2013
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Do you recall the day when personal and business computers first came on the market, along with the notion that they would put people out of work? I can recall buying the first personal computer for my son, a Commodore 64, and not having a clue how to work it; then taking a continuing education class at the local high school on computer basics and programming; and seeing the text "Syntax Error” forever etched into my personal database.
First flat screens replaced the thick tube-type televisions, followed by LED, LCD, and Plasma screens with 3 D capability. Then came phones with more power than computers, tablets with cameras, and the list goes on—what’s next?
Keeping current with the latest technology is expensive and challenging. Five years ago we updated our office servers, desk top computers and software programs to the latest and greatest of its day. Today we are once again updating our systems and software in order to better serve our customers.
IAEI is not standing still and watching technology pass us by. I’m very excited to announce that IAEI has embarked on two new initiatives that will be coming to a screen near you.
Redesigned and Updated Website
First, we are launching a fully redesigned and updated website. After months of brainstorming, planning, and data transferring, we created a fresh new look with user-friendly navigation that will provide new features such as an online membership community, accessible personal profiles, and instant social networking. Within this secure online community, each section, chapter and division will have its own homepages in which to create an online presence. Committees will manage the assignments for which the group is responsible. Membership rosters will be accessible, as will forums and photo galleries; online tools such as multimedia, and RSS feeds will also be available for your use. Social networking will be taken to new heights with features that will allow members to actively connect and collaborate with each other as well as grow professionally.
Each member will have control over his or her profile, deciding which information to allow others to see. If they are members of a committee, they will have access to that particular committee. After you have logged in, you may edit any of this information. Your Profile Home page can be accessed from any page on the site.
Even with all the latest features, our website will continue to provide you with the latest up-to-date industry news and events as well as information on our products and services. So I encourage you to explore our new website. To get you started, we have included Quick Link buttons to the new features on our homepage.
Interactive Version of IAEI Magazine
Along with our newly redesigned website, we will be releasing an interactive version of IAEI magazine downloadable through App Store, Newsstand, or Google Play, and viewable on iPads, Samsung Galaxy and Kindle Fire. Smartphone viewing will be available in April.
Through the interactive version, valuable information will be available in real time. When changes or new information are added, you will receive a Push Notification alerting you of the latest updates and keeping you current and in-the-know.
For authors, interactive makes sharing information boundless with capabilities such as video links, photo galleries or drawings, links to additional resources or reports, designs or any other instant information that will enrich their articles. Our imagination and ever-growing technology define the limits of what IAEI magazine can become and be able to offer IAEI members.
IAEI interactive magazine will encourage social sharing on Twitter, Facebook, Tumblr, Pinterest and email. With instant web access, posting feedback, consulting and comparing with others in the electrical industry will be instantaneous. Interact and follow your favorite authors through their Twitter feed or LinkedIn account as they keep you up-to-date on the latest news in the electrical industry. All these links will be at your fingertips; just touch, swipe, clip and share, watch, or purchase from our online store. The choice is yours.
Graphically, we’ve come a long way from the unassuming 20-page, letterpress publication called the News-Bulletin that debuted in March 1929, but we still share information, facts, shortcuts and — always — safety requirements.
For years we’ve had both a digital and a blog version of the magazine on the website, but now the interactive version adds another dimension to each article.
It is still our voice — louder, more persuasive, and now interactive!
IAEI Interactive will be available to members for free. For others, it is subscription based. The preview version is free to everyone for a limited time. Go to the App Store, Newsstand or Google Play and try IAEI magazine for yourself.
Read more by David Clements
Follow Dave on Twitter @DavidEClements
Posted By Thomas A. Domitrovich,
Friday, March 01, 2013
Updated: Wednesday, February 13, 2013
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Recognizing shock hazards can be difficult to the untrained or inexperienced eye on job sites and especially areas / facilities that have experienced storm damage. An electrocution is the result of coming in contact with a lethal amount current. Shock protection comes in many forms with ground-fault circuit interrupters (GFCIs) being that last line of defense of protection; as long as you are lucky enough that this type of protection has been installed and installed correctly. There are many ways to stay safe, we simply need to train our eyes and implement the correct procedures and tools to facilitate it.
Based on data from the National Institute for Occupational Safety and Health (NIOSH) National Traumatic Occupational Fatalities (NTOF) surveillance system, electrocutions were the fifth leading cause of death from 1980 through 1995. The 7,326 deaths caused by electrocutions during this period accounted for 7.8% of all fatalities in the workplace and averaged 488 deaths per year. Electrocutions were fifth as compared to motor vehicle incidents (#1), machine related deaths (#2), homicides (#3) and, finally, falls (#4). Yes, it is hard to protect from something you can’t see, but there are lines of defense that you can use to ensure you do not come in contact with energized conductors and/or equipment.
Based on data from the National Center for Health Statistics (NCHS), the total number of electrocutions in the United States has decreased from 670 in 1990 to 400 in 2000. This is a reduction of 40%. During this same period, an estimated number of electrocutions related to consumer products decreased from 270 to 150, a whopping 44%. The work we do in codes and standards is driving these numbers in the right direction. Product standards are making the necessary changes to ensure products are more robust with this regard, installation codes like the NEC are including changes that help to provide the protection needed in new structures being built and work practices standards like NFPA 70E help to address safety in the workplace. On top of all of this activity, we are more educated on the topic of shock protection through articles such as this and IAEI training events like those held across the country every day.
Figure 1. Electrical tape or similar methods are not a fix for these types of severe neglect.
Lines of Defense
There are many ways to avoid coming in contact with energized conductors and equipment and there are various documents that help us understand how to do just that. The primary document that comes to my mind on this topic is the National Fire Protection Association’s (NFPA) number two best seller, NFPA 70E, "Standard for Electrical Safety in the Workplace.” In addition to this document, the National Electrical Code, NFPA 70, also helps. Let’s review some important lines of defense.
Grounding and Bonding: NEC 2011’s Article 250 takes a total of 31 pages to help ensure the grounding and bonding of your system is such that equipment type ground faults have the lowest amount of impedance possible, resulting in them being high enough to be overcurrents that are cleared by the overcurrent protective devices in the circuit. Ground faults can be overcurrents if they are high enough to exceed the ratings of the conductors and other equipment. In fact, NEC 2011 Article 100’s definition of overcurrent includes ground faults; it states that an overcurrent is "any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault.” By ensuring an effective ground path, overcurrent protective devices can do their job in clearing these dangerous faults that if left unattended due to high impedances, could result in fires and even electrocutions should someone touch these energized parts. Acting to de-energize problem circuits before a person comes in contact with them or the equipment they energize helps avoid an electrocution from occurring.
Distance: Putting distance between yourself or others and a hazardous location is one sure way to prevent electrocutions. Barriers and guards can help ensure only qualified individuals are in work areas. NFPA 70E has provisions for limited approach boundaries and advises that physical mechanical barriers should be installed no closer than the restricted approach boundaries defined within that document. It’s advisable to use non-conductive barriers, especially where they may come in contact with energized parts. Tools also help to put some distance between you and the work you are performing that may present opportunities for you to come in contact with energized equipment. Tools such as communicating management systems will provide the ability to open or close protective devices or switches from the safety of an office well away from the equipment. Hot sticks and similar type devices also facilitate the separation needed. Your equipment, though, must be well maintained and inspected before every use.
Insulated Tools: Insulated hand tools, matting and other personal protection equipment (PPE) can help prevent electrocution should you or your tool come in contact with energized equipment. Ensure your tools have not fallen in to disrepair, as insulation that is there to protect you could be jeopardized. You may have hand tools with insulated handles worn through, creating safety concerns. Figure 1 is a severe case of neglect. Electrical tape or similar methods are not a fix for these types of problems. There comes a time when if your tools don’t pass basic visual inspections, they should be replaced. Some tools require more than just a visual inspection; specific testing to identified standards may be required. NFPA 70E’s Table 130.7(C)(14), "Standards on Protective Equipment,” provides reference documents for various PPE items you will use on projects.
Rubber protective products require visual inspection before every use. Table 130.7(C)(14) has the following with respect to these types of products. Rubber Protective Products — Visual Inspection Standard Guide for Visual Inspection of Electrical Protective Rubber Products ASTM F 1236 - 96(2007)
Figure 2. This drawing Illustrates that the ground-fault sensor must have both conductors passing through the device. This sensor senses an imbalance in current and sends the difference of current between that which is going to the load and that which is coming back from the load to the relaying equipment.
For even more detail on rubber insulating equipment, NFPA 70E has Table 130.7(C)(7)(c), "Rubber Insulating Equipment, Maximum Test Intervals,” yet another good example of testing frequency and reference test standards. This table advises that blankets should be tested before first issue and every 12 months thereafter. Gloves should be tested before first issue and every 6 months thereafter. Gloves are tested to ASTM F 496. This table addresses blankets, covers, gloves, line hose and sleeves.
Personal Protective Equipment: Your personal protective equipment is important on every job. You must not only maintain your PPE, but you must also ensure you are using the correct equipment for the job at hand. NFPA 70E 130.7(C)(15), "Selection of Personal Protective Equipment When Required for Various Tasks,” is the perfect reference for this line of defense. This section includes a wealth of information providing guidance on which PPE should be utilized for various types of projects. This section includes those tables illustrated above as well as hazard / risk category guidance to help convey which PPE is required when working on various types of equipment.
Working De-Energized / Lockout-Tagout: Yet one more way to ensure your team avoids electrocution is to work on de-energized equipment. We should always strive to work de-energized. Proper lock-out tag-out procedures should be followed, and effective testing techniques to ensure equipment is de-energized are important as well.
GFCI Protection: The acronym GFCI is used quite often and if I were to hazard a guess, I would say that very often it is used incorrectly. It is not only important to use terminology correctly but to also understand the limitations of the various ground-fault devices out there to facilitate in their proper application. GFCI protection is your last line of defense that is hopefully provided in your situation. The next few sections will take a high level look at a few different types of ground-fault devices.
Safety Plan: Last but not least is your safety plan. This is that document that pulls together all of your safety procedures and policies providing your plan to electrical safety. This document is your springboard for safety training and reporting. It is the glue to all that is safety for your organization.
Figure 3. This image demonstrates all of the conductors passing through the sensor, as it is the job of the sensor to ensure all current is accounted for. Only 2-pole devices are adequate for these types of applications.
UL 943 vs. UL 1053 Ground-Fault Protection Devices
We’re talking people protection versus equipment protection when we set these two UL standards side-by-side. A device tested to UL 943, "Ground-Fault Circuit Interrupters,” is one that is intended for the protection of personnel. The Scope of UL 943 reads as follows: "This Standard applies to Class A, single- and three-phase, ground-fault circuit-interrupters intended for protection of personnel, for use only in grounded neutral systems in accordance with the National Electrical Code (NEC), ANSI/NFPA 70, the Canadian Electrical Code, C22.1 (CEC), and Electrical Installations (Use), NOM-001-SEDE. These devices are intended for use on alternating current (AC) circuits of 120 V, 208Y/120 V, 120/240 V, 127 V, or 220Y/127 V, 60 Hz circuits.”
A UL 1053, "Ground-Fault Sensing and Relaying Equipment,” device on the other hand is one that is designed to protect from equipment damage due to ground fault. The scope of this standard reads as follows: "These requirements cover ground-fault current sensing devices, relaying equipment, or combinations of ground-fault current sensing devices and relaying equipment or equivalent protection equipment for use in ordinary locations that will operate to cause a disconnecting device to open all ungrounded conductors at predetermined values of ground-fault current, in accordance with the National Electrical Code, ANSI/NFPA 70.” These types of devices help to prevent burn downs and other types of electrical fires.
A ground-fault device is going to be present to serve one of two basic needs: provide people protection or provide equipment protection. We’ll discuss the applications of both of these types of devices after covering some of the basics of ground-fault protection to help us understand their goals and their proper application. Suffice it to say that a device listed to UL 943 is designed for personnel protection and a device listed to UL 1053 is designed for equipment level ground-fault protection. Let’s take a quick refresher on how a GFCI device works before addressing the differences between these two basic types of devices.
Ground-Fault Device Operation Basics
A ground-fault device operates off of the basic principle of differential current; that current which goes out to the load through the hot conductor has to come back from the load over the neutral conductor. (Reference figure 2). The conductors involved are the expected paths for current. This applies to 2-wire, 3-wire or even more conductors in the case of three-phase installations. A three-phase device may appear to get a little more complicated due to phase angles and more hardware that needs to be installed, but you are still working off the basic fundamental principal of what goes out must come back over the expected paths, the conductors for the circuit.
A ground-fault device will employ two key components that work together to determine if ground-fault current is flowing. The system is comprised of sensing equipment and relaying equipment. The sensing equipment will come in the form of a current transformer that can be placed at various locations within the circuit. Sensing equipment and relaying equipment do not have to all be in one self-contained device. Industrial power systems will employ separate sensing equipment in the form of current transformers around bus bars or large conductors that must be wired back to the equipment. In the case of smaller ground-fault type devices like those you will find in residential applications, both sensing equipment and relaying equipment are located in the same small enclosure. Just to keep things simple, we’ll address what you would find in a residential ground-fault device as both of these key components are typically located within one small compact device.
Your basic ground-fault breaker or receptacle-type devices include a current transformer that surrounds the hot and neutral conductors of the circuit and a small circuit board that receives the signal from this sensor and makes the decision of whether or not to open the circuit. The conductors that pass through the sensor window must include all hot and neutral conductors serving the load. This is why, for shared neutral applications, you cannot apply a handle tie to two single-pole breakers and share the neutral. Both breakers need their own neutral return path. A two-pole GFCI device ensures the integrity of current flow through the internal current transformer for proper operation. (Reference figures 2 and 3 for examples of this).
Ground- fault currents are seeking the path of least resistance back to the source. NEC 2011’s Article 250 takes the time in a total of 31 pages to help you ensure the grounding and bonding of your system is the best it can be. For equipment ground faults, you want a low impedance path to the source. Article 250 helps get you there. Every wire connector and connection point in the grounding system is important to achieve your goals. If you have a good low impedance path to ground, your equipment type ground faults will become overcurrents that are acted upon by your standard overcurrent protective devices up stream.
Personnel Protection – UL 943
Now that we have a basic understanding of how ground-fault devices work, let’s explore what makes a ground-fault device a GFCI, one that is intended to protect personnel. To get electrocuted, three things are important: (1) the amount of current, (2) the path it takes through the body and (3) the amount of time it flows. A GFCI device does not know the path that current takes through your body and can have no control over that, but it can detect the amount of current and identify when to open the circuit. UL 943 defines these two key parameters for these types of devices. A GFCI device is designed to not trip for currents less than 4 mA and to always trip for currents above 6 mA. The amount of time it takes is determined by a couple of equations. For low-resistance faults, the equation is as follows:
For high-resistance faults, the equation is as follows:
So as an example, for a high-impedance fault which would result in a small current flowing, say 6mA as an example, the GFCI device as per the above equation will take 5.59 seconds to trip.
In reality, all GFCI devices trip much faster than that required by UL 943 and a 6mA fault would normally take no more than 0.1 seconds, with some margin for error, to be cleared by an off-the-shelf GFCI device.
To understand what this means to a person, the following table is used by many documents to describe the effect of current.
A GFCI device is designed to open the circuit to avoid the problems identified in table 1.
Table 1. The effect of current on humans
Equipment Protection – UL 1053
A device designed to this standard for equipment level protection is not meant to protect a person from electrocution. The UL standard for this type of device does not specify the current level at which it will pick up; it merely defines, amongst many other requirements, the amount of time it can take to clear. A UL 1053 device establishes the time criteria for clearing a ground fault at the pick-up level defined by the manufacturer of the device.
This performance criterion is not based on when the heart goes into defibrillation or when it may stop. This is an important thing to remember as it would be a mistake to apply a UL 1053 device, thinking you are going to achieve personnel protection.
Table 2. A UL 1053 device establishes the following as the time criteria for clearing a ground fault at the pick-up level defined by the manufacturer of the device.
There are many ways to prevent electrocution. Leverage your various lines of defense to avoid coming in contact with energized conductors and/or equipment; and as your last line of defense, ensure you have employed the correct GFCI device for personnel protection. GFCI devices are not required on every circuit at every voltage and for every application. Do everything you can to keep your distance, use insulated equipment, take care of your tools, and think and observe before proceeding in and around hazardous areas.
As always, keep safety at the top of your list and ensure you and those around you live to see another day.
Read more by Thomas A. Domitrovich
Posted By Joseph Wages, Jr.,
Friday, March 01, 2013
Updated: Wednesday, February 13, 2013
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The National Electric Code, in Article 650, contains the electrical requirements for pipe organs. Pipe organs have been in existence since early Greece in the third century B.C. They were viewed at one time as the greatest of human achievement. But why on earth is there an article in the NEC dealing with these music producing instruments?
A Little History
Pipe organs have been around a long time. In the early years, these devices used water pressure for the production of wind to produce their all too familiar sounds. Unlike a piano, the pipe organ continues to produce its desired sound as long as the pedal is depressed. Many of us have fond memories of hearing these at churches and cathedrals from around the world. Their unforgettable sounds have been played in musicals and movies such as The Phantom of the Opera. Who can forget those eerie (or to some, wondrous) sounds!
Many dignitaries have been laid to rest in the presence of the sounds of this instrument. Presidents and other world leaders have been resting in state or officiated over with the accompanying sounds from the pipe organ. Thousands of weddings have been officiated over and joyful lifetimes begun in buildings that employ these magnificent instruments. The pipe organ has played a large part in many religious ceremonies throughout the ages and continues to do so to this day.
The oldest playable organ was built in 1430. It is known as Organ Sion Switzerland Notre Dame de Valere. As one might expect, there are many locations in Europe that have famous pipe organs that have been around for hundreds of years. The largest pipe organs in the United States are found in Atlantic City, New Jersey, and Philadelphia, Pennsylvania. One of the most well-known locations is the Washington National Cathedral. There are many official events held yearly at this historic location. A recent earthquake on the East Coast had many concerned about whether there had been any extensive damage to the structure or contents of the building. There had been some damage to the building but the organ was unharmed. One construction worker remarked, "God watches over this building.”
Electricity and Electronics
The advent of electricity led inventors to replace mechanical and wind action with electro-pneumatic and electric action. By using low-voltage direct current (dc) electricity, keyboards could use electronic magnets with valves and electro-mechanical actions to play the pipe work. Electricity also allowed other musical sounds to be played with the organ pipes, mimicking the sounds of other instruments.
The pipe organ also has a long history in the National Electric Code. I have researched our library at the IAEI back to the 1930 edition; and, as expected, there exists an article covering the pipe organ. It might be in earlier versions, as well, but I did not have them for my use at this time. Although the article has seen a few changes over the years, the pipe organ is still installed or maintained using the valuable information found within the NEC requirements.
Article 650 is a relatively short article compared to others in the NEC. One would not think that an article that is not well-known would still hold any relevance in the electrical industry. Believe it or not, there were changes within this article between the 2008 and the 2011 code cycle! This article falls under the purview of code-making panel 12 of the National Fire Protection Association. It is a pertinent article that has applications to a specific item that many in this industry may never have an opportunity to work on or inspect. But the application it serves for the pipe organ is relevant and important to the safety of the equipment, the public, and its user. Here is a brief overview of Article 650, Pipe Organs.
650.4 Source of energy is a transformer-type rectifier, not to exceed 30 volts dc.
650.5 Grounding requires the rectifier to be bonded to the equipment grounding conductor according to 250, Parts V, VI, VII, and VIII.
650.6 Conductors have restrictions of size, insulation, cable, and covering.
650.7 Cables shall be securely fastened in place and are permitted to be attached directly to the organ structure without insulating support, but not in contact with other conductors.
650.8 Overcurrent protection must be provided for 26 AWG and 28 AWG conductors at not more than 6 amperes; other conductor sizes are to be protected according to their ampacity.
One of the 2011 changes occurred in 650.3 concerning other articles in the NEC that apply to this article. Two additions were made to this section to include (A) Electronic Organ Equipment and (B) Optical Fiber Cable. Electronic organ equipment shall also conform to Article 640, Audio Signal Processing, Amplification, and Reproduction Equipment. Optical fiber cable shall conform to Article 770, Optical Fiber Cables and Raceways.
Another change occurred within 650.7 as it applies to the installation of conductors. The change deals with abandoned cables that do not terminate at the equipment. The change states that the cables shall be identified with a tag.
Photo 3. The introduction of electricity led inventors to replace the mechanical and wind action in pipe organs with electric action. Then, of course, that installation was covered in the NEC — in 1930 [the earliest version in the IAEI library]. Shown here are representative copies of the Code from the 1930s, 1950s, 1960s, 1990s, and the current 2011 Code.
But keep in mind that there are other requirements found in the NEC that apply to pipe organs. An example is found in Article 250.112(B) which speaks to a requirement for an equipment grounding conductor. This requirement applies to the generator or motor frame of a pipe organ, unless effectively insulated from ground and the motor driving it.
Pipe organs have had an impact on society for approximately 2300 years or more. With proper maintenance and installation practices, they will continue to fascinate and invigorate another generation of people. The articles that some believe are insignificant within the NEC often play a bigger role than some might expect. Take time to know the sometimes overlooked articles in your code book. They might just bring about a new appreciation for items like the pipe organ.
Read more by Joseph Wages, Jr.