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Article 110, Requirements for Electrical Installations

Posted By Randy Hunter, Sunday, May 01, 2011
Updated: Wednesday, January 09, 2013

In the last issue we discussed theNECrequirements up through 110.14, Electrical Connections, so we will start with 110.15, the requirement for identifying the high leg. Now you’re probably asking, what is ahigh leg? To answer that, we have to review some of the basics related to voltages and transformer windings and connections. We have two basic transformer configurations, wye (Y) and delta (∆). Using one of these configurations, utilities supply power to premises with different voltages, such as 120/208Y, 277/480Y, 120/240 single-phase, 120/240 three-phase ∆, and 480 ∆. (See figure 1.) In a Y system, we have equal voltage from each leg or phase to the grounded conductor which is connected to the center of the Y. In a ∆ system, there is an "open” delta which uses two transformers windings, and a "closed” delta which uses three transformers windings. In a delta system, one of the legs can be center tapped and grounded which makes 120 volts to each corner point of the leg from which it is tapped. Now we are ready to solve the mystery of the high leg: it is the leg carrying the voltage between the center-tapped grounded connection and the point of the triangle opposite of the leg tapped. The voltage to ground from the high leg is 1.732 times the single-phase center-tap voltage. As an example, if a 240-volt ∆ has a center tap to provide 120-volt single-phase, the opposite corner voltage will be 208 volts.

Figure 1. The top example is a Y connected system, which will provide voltages of 120/208 or 227/480. The bottom example is a delta system, which will produce 120 volts between the center tap in the bottom winding and each adjacent leg, however between the center tap and the top leg is what we call the high leg, as described in the article.

Now that we have discovered what a high leg is, the code requires that we identify it in a certain way. The special marking is necessary since 120-volt equipment doesn’t work very well or very long when connected to over 200 volts. Therefore, the high leg must be durably and permanently marked by an outer finish that is orange in color or by other effective means. How do we do that? I once had an inspector insist that I paint the busing of an electrical panel red to identify the high leg. Disagreeing with an inspector is never a comfortable situation; however, I just couldn’t do what he was asking. It would have created code violations for contamination of electrical equipment, and the color should have been orange rather than red. So, ignoring all common sense, I decided I just couldn’t let this go and had to find a way to tell the inspector he was wrong. The best way I could think of was to get a code book and discuss it with him. After reviewing the code, we came to an agreement that we weren’t going to paint anything and that orange was the right color for identifying the high leg. The code gives us a basic method to use and that is to place the identification at each connection point, and this is only needed at locations where the grounded conductor is present.

Arc-flash hazard warning

Moving on, we come to the requirement for arc-flash hazard warning (110.16), which simply states that we need to label equipment to let qualified persons know of the hazards present if energized. The labeling is not required for dwelling units. (See figure 2) for a label example.) Also in 110.18 we learn that any arcing parts must be enclosed or separated and isolated from combustibles. Keep in mind, simple items such as switches and receptacles have the ability to produce arcs, so we make sure they are enclosed in boxes.

Equipment label information

In 110.21, manufacturers are required to label equipment with information including their name, trademark or other descriptive identification, and other markings that indicate voltage, current, wattage or other ratings. This is one of the most valuable things in the code for both the electrician and inspector, since it allows both to make sure they have utilized the product in the proper way. If you come across an unfamiliar marking on equipment, it is handy to have a UL White Book which provides information on equipment listing requirements and marking guides.

Identification of disconnecting means

Identification of disconnecting means is detailed in 110.22, and requires that the installer shall legibly mark each disconnecting means. This is the case unless the disconnecting means is located in such a way as to be very obvious as to which device to which it is connected. It then goes further to discuss series combination systems, please take a moment to read the code language and find out how these systems are to be labeled with specific language.

Figure 2. This is an example of the arc-flash warning label and some of the locations it would be required

Available fault current

Now we come to an entirely new portion of the code in 110.24, Available Fault Current. As this is new, we will take a moment to cover this in detail and give you my opinion regarding the new language. This has been broken into two parts, Field Marking and Modifications. First is field marking, which requires the service equipment (other than dwelling units) to be marked with the maximum available fault current and the date the calculation was performed. Who is responsible for this labeling? The contractor will probably have the label made and install it. Who does the calculation? This comes from the design professional who has been in contact with the serving utility, has taken the figures provided, and has then calculated what the exact available fault current is at the service after taking into account the distance, conductor size, and more. So what is the purpose of the labeling? It simply gives us a snapshot of the exact conditions that exist at that exact time period when the label is applied.

How valid is the marking if changes are made anywhere on the system, such as a transformer change or added loads (which could include motors or a variety of other items) that could affect the calculated number? With this question in mind, the next paragraph in the code, 110.24(B), Modifications, then addresses what needs to be done. If system changes cause any change in the available fault current, then it needs to be re-calculated and re-labeled.

Photo 1. The working "cube”

So why do we need this marking? In my opinion, this is a good requirement that provides a record which is attached to the service equipment as to what the fault current is at a particular time. This will make it easy to inspect and to verify that the service equipment is sized adequately to handle the available energy. Also, it provides valuable information to anyone servicing the equipment at a later date, which should allow us to maintain the code-compliance of the installation. The only down side is that if a transformer changeout is performed by the serving utility, someone has to re-label the equipment to match the available fault current unless the new transformer is exactly the same as the old one. The utility is not responsible for the re-labeling, so the facility owner must be aware of the change and make sure their service equipment is re-labeled. For a variety of reasons, this re-labeling may not happen in many cases, so a little detective work may be necessary for the person servicing or maintaining the equipment. It might be necessary to locate an original set of plans to verify any modifications. Still, taking all the possible difficulties into consideration, this requirement is a good starting place to insure equipment isn’t misused.

Spaces about electrical equipment

We are now closing in on the last thing we are going to cover in Article 110, which is Spaces about Electrical Equipment. The requirements start in Section II of Article 110 with 110.26. The requirements of this article have always been held in the highest regard by myself and other inspectors, as this outlines the areas needed to safely approach, service and exit from locations with electrical equipment. I’ve always considered these requirements to be essential for life safety. If a person were to be injured and the proper clearances were not there, the results could be catastrophic. Due to this, I’ve always taken this portion of the code very seriously.

The first item to be covered is access to the working space, which shall be provided as a clear and maintained area to allow ready and safe operation and maintenance of the equipment. After we get access to the area, we next have to define the actual working space right in front of the equipment. Depth of the working space is outlined in 110.26(A)(1), and the requirements vary according to the voltage and what is directly across from the equipment, such as a grounded surface or other electrical equipment. The distances vary from three feet to four feet, according to the exact conditions. Please review this section as it is written very clearly and in detail, and it has several items to be considered when applying the requirements.

Figure 3. Pictured are the condtions for entrance and egress about large equipment, in the above example if the door was opposite from the equipment (at the top of the room in this example) then that would create a clear unobstructed egress path. a=required working clearance.

Next we have to address the width of the working space. As you can see, the code addresses each dimension separately. The width must be a minimum of 30 inches, or be equal to the maximum width of the equipment (whichever is greater) and in all cases shall permit the opening of doors or hinged panels a minimum of 90 degrees. Don’t confuse this item and think that every door or hinge panel must open 90 degrees. TheNEConly requires that the space shall permit the opening, not that the doors will open, since that is a product standards issue.

Next we address the height of the working space, which shall be a minimum of 6½ feet or the maximum height of the equipment, whichever is greater. If we have other equipment associated with the electrical installation which is located above or below the equipment, it is permitted to extend 6 inches past the face of the equipment and not be considered a code violation to the working space. One important thing to keep in mind on this 6-inch allowance is that electrical meters are exempt from this limitation. This exception was added to allow for all the new "super” meters, since they keep getting bigger and extending farther from the attachment point. To sum up the actual "cube” of working space we’ve just outlined, as you stand in front of any gear, picture yourself inside a large box where the width, height and depth are equal to the dimensions as described above (see photo 1). The last requirement for working space is that we must not use the area for storage. This means no cleaning supplies, boxes, or anything else in the working space.

Entrance and egress

The next set of requirements in 110.26 covers the entrance and egress to and from the working space. The basic requirement is at least one entrance of sufficient area shall be provided for access to and egress from the working space described above. If we encounter what is referred to as "large equipment” we have added requirements for entrance and egress. First, what constitutes large equipment? It is equipment which is rated 1200 amps or more and is over 6 feet wide. Once you reach this size, you have to have a means of entrance and egress at each end of the working space. Also in the same paragraph as the two exit requirements, we finally have a size for the entrance, which is a minimum of 2 feet wide and 6½ feet high. There are alternates to the double entrances rule, including if you have a totally unobstructed egress path, or you have double the working space as previously described. However, getting electrical rooms this large is rare as architects hardly ever give us extra room, mainly because electrical rooms do not generate any revenue within the building. (See figure 3.)

Did you notice that we talked about the size of the entrance without actually mentioning doors? Doors may or may not be used, and are often triggered by the requirements of other codes, such as the building codes. When we have equipment rated 1200 amps or over, and we have personnel doors for the entrance and egress located within 25 feet of the required working space, then these doors must open in the direction of egress and be equipped with panic bars, pressure plates or other devices that are normally latched but open under simple pressure. This requirement is to allow rapid egress from an electrical room in the event of a dangerous event. This does not mean every door in the building within 25 feet, only those providing direct access to the electrical room. These requirements often cause problems for the electricians as we have nothing to do with the building design, room size and specification of doors or hardware, so please be proactive and inform whoever needs to know about these requirements as early as possible in the building process. This can save a lot of hair pulling when it comes time for final inspections. The code also requires illumination for working spaces about electrical equipment, as detailed in 110.26(D).

Dedicated equipment space

The last item we’ll cover in Article 110 is the requirement for dedicated equipment space. This is another one of those requirements which is frequently violated due to the fact that other trades are often required by their design professionals to install systems foreign to the electrical system above our electrical equipment. First, we don’t worry too much about outdoor installations, so I’m going to concentrate on the requirements for indoor installations. These requirements are outlined in 110.26(E)(1)(a) through (d), and the main items are as follows: the space equal to the basic footprint of the equipment and extending for a distance of 6 feet above the top of the equipment or to the structural ceiling is considered dedicated space, meaning that any piping, duct leak protection apparatus or other equipment foreign to the electrical installation is not permitted. I’ve witnessed all kinds of creative ways of trying to satisfy this requirement under the guise of structural ceiling. However, the structural ceiling is defined as an element which is required to maintain the stability of the building, not some infill framing element creating a ceiling, and the code addresses this in (d). One exception is a suspended ceiling with removable panels, which are permitted in this space due to the easy access and removal of these systems. Sprinkler systems are permitted above the equipment as long as they comply with the dedicated space requirement. If we have foreign systems located above the dedicated 6-foot space, then we have to make sure that protection is provided to ensure any leakage from the systems will not cause damage to our electrical equipment. This usually is achieved by installing drip pans to protect the gear, but remember that the drip pans must also be above the dedicated space. I’ve heard a lot of discussion on the need for this requirement, but the best argument is that this space is required for servicing and installation during future work to be performed on the electrical system.

Part III of Article 110 deals with the requirements for over 600 volts, but based on the fact that most installations are under 600 volts and those over 600 volts require considerable specialized knowledge, these articles will continue to concentrate on under 600-volt installations.

In the next issue, we will dive into Chapter 2 of theNEC,where we start with grounded conductors and then move on to branch circuits and more.


Read more by Randy Hunter

Tags:  Featured  May-June 2011 

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