Through these articles, I hope you’re developing a better understanding of the National Electrical Code. This edition will get into branch circuits and pick up where we left off last month, which covered an introduction to finding requirements in the NEC for branch circuits and feeders. It also talked about the different types of branch circuits the NEC permits. This month’s article will cover how the NEC requires users to identify branch circuit conductors and look at certain voltage limitations the Code has in place for branch circuits.

First, let’s start off with a quick discussion of conductors that make up a branch circuit. As we learned early on, for electrical current to flow in a circuit, it needs a complete path where electrons can flow between points of different electrical potentials. In other words, a circuit will always have a supply and return path for current to flow. In a simple two-wire circuit, this relationship is fairly apparent. In multi­wire branch circuits, this relationship is a little less obvious, as there is some current returning on circuit conductors and some on the neutral conductor shared between circuit conductors. Therefore, it is critical that we can easily identify these conductors at any point on the system.

A quick refresher

Section 210.5 covers the identification of branch circuit conductors. Since I have already gone over the identification of equipment grounding conductors (EGCs), let’s refresh our understanding of Article 250. Remember that the EGC can be bare, covered or insulated. But the EGC can also be wire-type, a raceway or cable sheath, or any other means permitted by 250.118. Except for a wire-type EGC, this conductor is typically easy to identify since it is physically different from the circuit conductors. 

However, when it comes to the wire-type EGC, it is critical this conductor doesn’t get mixed up with the circuit conductors, as normally non-current-carrying metal equipment parts are connected to the EGC. Therefore, if a wire-type EGC is insulated, the insulation needs to be green or green with one or more yellow stripes. Of course, the easiest way to achieve this is to use a wire with insulation that matches, but Article 250 has a couple of options listed in 250.119.

That leaves us with identifying a branch circuit’s circuit conductors. This consists of identifying ungrounded and grounded/neutral conductors. Grounded/neutral conductor also carries critical safety implications. Incorrect installation can lead to current flowing on conductive material not intended for current and can lead to serious danger for occupants and the building itself. I have a story or two about finding out the hard way that neutral current was flowing where it was not supposed to be! To identify the grounded conductor, head to Article 200. 

Color identification

Section 200.6 specifies how to identify the grounded conductor. The most common and obvious way is to install a wire with a continuous white or gray outer finish. However, there are other options. 

One method is to install a conductor with three continuous white or gray stripes along an insulation of any color other than green, as green is for the EGC. For conductors 4 AWG and larger, it is not uncommon to identify the grounded conductor at the time of installation. This can be done using a distinctive white or gray marking at the conductor’s termination. Usually this is done with marking tape, but it is important to note that the marking must completely encircle the conductor. 

Next, we must properly identify the ungrounded conductors in the circuit. More commonly referred to as the “hot” or “phase” conductors, the ungrounded conductors are the circuit conductors fed directly from the overcurrent protective device. Since we have already assigned white, gray and green to identify the grounded conductors and EGC, you can probably guess that the ungrounded conductors will need a different color. That leaves the ungrounded conductor with plenty of options for identification. Basically, any insulation color other than white, gray or green is going to identify an ungrounded conductor, provided there are not three continuous white or gray stripes along the insulation. 

However, the NEC is not going to let us off the hook that easily; there is more to it than just picking any random color.

Where the NEC steps in and guides us is for installations where more than one nominal system voltage exists. For instance, consider a building supplied by a 480/277V wye-connected system that uses transformers to derive a separate system operating at 208/120V to supply receptacles. Obviously, it would be chaos if every conductor had black insulation or if there was no rhyme or reason to the colors used. 

So, the NEC requires a color-coding process be chosen for each system for identification. In the United States, this is typically done by using black-red-blue-white for all systems with 120V to ground and brown-orange-yellow-gray for systems with 277V to ground or other 480V systems.

Ungrounded conductors must be easily distinguishable at all termination, connection and splice points in the system. This can be achieved by color-coding, marking tape or another approved method such as tagging. 

The NEC also requires the chosen identification to be posted at the point where the circuit conductors receive their supply, such as the panelboard, or be documented and readily available.

Voltage limitations

Since we are talking about voltage systems, let’s look at some voltage limitations the NEC puts on branch circuits. The easiest way to approach branch circuit voltage limitations is to look at what the circuit is supplying or where the circuit is being installed. In dwelling units and guest rooms or suites of hotels, motels or similar occupancies, the branch circuit is limited to 120V (nominal) to ground for lighting, cord-and-plug connected equipment that draws 12A or less and motor loads ¼ hp or less. 

Outside of this restriction for dwelling unit-like occupancies, the rest of the voltage limitations listed in Section 210.6 look like a long list of permissions. To ensure branch circuits are installed correctly, determine the supply voltage requirement for the equipment being supplied and make sure you aren’t supplying something that violates the limitations in place that require 120V to ground in dwelling units and guest rooms or suites of hotels, motels or similar installations.

Identifying which conductor of a branch circuit is which and understanding limitations placed on branch circuits is critical to meeting the purpose of the NEC in 90.2(A). Remember, if a premises wiring system conductor is any color other than white, gray or green, it is most likely an ungrounded or hot conductor, and interrupting a white or gray conductor turns one end into an ungrounded conductor if the circuit is still energized—the result is commonly referred to as an open neutral. 

Next month’s article will jump ahead a little in Article 210. Until next time, stay safe and remember to always test before you touch! 

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