Article 215 covers the installation, conductor sizing, and overcurrent protection requirements for feeder conductors. The requirements for feeders have some similarities to those for branch circuits. But in some ways, feeders bear a resemblance to service conductors. It’s important to understand the distinct differences between these three types of circuits.

You can generally think of feeders as being the “middle set” of conductors in the power distribution scheme.

At one end, you have the service equipment, the separately derived system, or other supply source. At the other end, you have the final branch-circuit overcurrent protection device (OCPD).

Feeders are the conductors between these two ends. Let’s make sure we have a clear idea of what those two ends are.
• Conductors past the final OCPD protecting the circuit and the outlet are branch-circuit conductors [Article 100] and fall within the scope of Article 210.
• Service conductors are the conductors from the service point to the service disconnect [Article 100] and fall within the scope of Article 230.

If there’s no serving utility, and the electrical power is derived from a generator or other on-site electric power source, the conductors from the supply source are defined as feeders and there are no service conductors.

It’s easy to become confused between feeder, branch circuit, and service conductors, so it’s important to evaluate each installation carefully using the Article 100 definitions. Otherwise, you risk applying the wrong set of NEC rules.

Minimum size of current carrying conductors
You size feeder conductors differently from the way you size branch circuit conductors. With branch circuits, the OCPD size is known (e.g., it’s a 20A circuit) and you size the conductor accordingly.

But with feeders, you determine the load and then size the conductor and OCPD accordingly. The “accordingly” part for the conductors means the feeder must be the larger of 215.2(A)(1)(a) and 215.2(A)(1)(b):

(a) The feeder conductor must have an ampacity, before ampacity correction and adjustment of, not less than 125 percent of the continuous load plus 100 percent of the noncontinuous load, based on the terminal temperature rating ampacities as listed in Table 310.15(B)(16) [110.14(C)(1)].

(b) The feeder conductor must have an ampacity, after ampacity correction and adjustment, of not less than the load to be served.

See 215.3 for the feeder OCPD sizing requirements for continuous and noncontinuous loads. The three Informational Notes in 215.2(A)(1) will help you correctly size your feeders:

Informational Note 1: See Examples D1 through D11 in Informative Annex D.

Informational Note 2: To provide reasonable efficiency of operation of electrical equipment, feeder conductors should be sized to prevent a voltage drop not exceeding 3 percent. And the maximum voltage drop for the total of feeders and branch circuits shouldn’t exceed 5 percent.

Informational Note 3: See 210.19(A), Note 4, for voltage drop for branch circuits.

Now let’s look at a sample problem to illustrate 215.2(A)(1)(a).

Question: What size feeder conductors are required for a 100A continuous load and 100A noncontinuous load if the terminals are rated 75 DegrC?
Answer: 4/0 AWG ungrounded conductors.
Since the load is 100A continuous at 125%, and the 100A noncontinuous load at 100%, the feeder conductors must have an ampacity of at least 225A ([100A x 1.25] + 100A x 1.0 = 225A). According to the 75 DegrC column of Table 310.15(B)(16) [110.14(C)(1)(b)], 4/0 AWG has an ampacity of 230A.

Of course, there are exceptions to this rule:

Ex 1: If the assembly and OCPD are both listed for operation at 100 percent of their rating, the conductors can be sized at 100 percent of the continuous and noncontinuous load. However, equipment suitable for 100 percent continuous loading is rarely available in ratings under 400A.

Ex 2: This exception is new with the 2017 NEC. A section of feeder conductors that terminates in a junction box (at each end) to 90 DegrC terminals per 110.14(C)(2) is permitted to have an ampacity of at least 100 percent of the continuous and 100 percent of the noncontinuous load based on 90DegrC column of Table 310.15(B)(16) for 90DegrC conductor insulation. The 100 percent at 90DegrC feeder conductors are not permitted to extend into the supply or the load terminations to the feeder circuit.

Examples:
• A 400A feeder with 500 kcmil conductors (rated 380A at 75DegrC) on supply and load terminals, with 400 kcmil conductors (rated 385A at 90DegrC) between the supply and load ends.
• A 1200A feeder with three sets of 600k (420A at 75DegrC) on terminals with 500K (430A at 90 DegrC) between supply and load ends.

Ex 3: Neutral conductors must have an ampacity of at least 100 percent of the continuous and noncontinuous load.

Minimum size of neutral
The feeder neutral conductor must be sized to carry the maximum unbalanced load per 220.61. It must not be smaller than listed in 250.122 [215.2(A)(2)], based on the rating of the feeder OCPD.

Question: What size neutral conductor is required for a feeder consisting of 250 kcmil ungrounded conductors and one neutral conductor protected by a 250A OCPD, where the unbalanced load is only 50A, with 75DegrC terminals?
Answer: 4 AWG [based on Table 250.122].

Table 310.15(B)(16) and 220.61 permit an 8 AWG neutral conductor, rated 50A at 75DegrC to carry the 50A unbalanced load, but the neutral conductor isn’t permitted to be smaller than 4 AWG, as listed in Table 250.122, based on the 250A OCPD [215.2(A)(2)].

Sizing OCPDs
Feeder OCPDs must have a rating of not less than 125 percent of the continuous loads, plus 100 percent of the noncontinuous loads [215.3].

Ex: If the assembly and the OCPD are both listed for operation at 100 percent of its rating, the OCPD can be sized at 100 percent of the continuous load.

What about feeders with a common neutral conductor? Up to three sets of 3-wire feeders or two sets of 4-wire or 5-wire feeders can use the same neutral conductor [215.4(A)]. The neutral conductor must be sized to carry the total unbalanced load for all feeders as determined in Article 220, see 220.61.

Equipment grounding conductor
Feeder circuits must include (or provide) an equipment grounding conductor (EGC) of a type listed in 250.118. This EGC must terminate in a manner so that branch-circuit EGCs can be connected to it, and installed per 250.134 [215.6].

Ground-fault protection of equipment
Each feeder disconnecting means rated 1,000A or more supplied by a 4-wire, three-phase, 277/480V wye-connected system must be provided with ground-fault protection of equipment per 230.95 and 240.13 [215.10].

Two exceptions exist:
• The requirements don’t apply to a disconnecting means for a continuous industrial process if a disorderly shutdown will introduce increased or additional hazards.
• Equipment ground-fault protection isn’t required if ground-fault protection of equipment is provided on the supply side of the feeder and on the load side of the transformer supplying the feeder.

Ground-fault protection of equipment isn’t permitted for fire pumps [695.6(G)], and it’s not required for emergency systems [700.31] or legally required standby systems [701.26].

Conductor identification
An insulated feeder neutral conductor must be identified in accordance with 200.6 [215.12(A)]. The requirement that this conductor be insulated is new with the 2017 NEC.

EGCs can be bare. Individually covered or insulated EGCs sized 6 AWG and smaller must have a continuous outer finish either green or green with one or more yellow stripes [215.12(B) and 250.119].

Insulated equipment grounding conductors 4 AWG and larger can be permanently reidentified with green marking at the time of installation at every point where the conductor is accessible [250.119(A)].

If the premises wiring system contains feeders supplied from more than one voltage system, each ungrounded conductor, at all termination, connection, and splice points, must be identified by phase or line and system, in accordance with (a) and (b) [215.12(C)(1)]:

(a) Identification Method. Identification can be by color coding, marking tape, tagging, or other means approved by the authority having jurisdiction.

(b) Posting of Identification Method. Such identification must be documented in a manner that’s readily available, or it must be permanently posted at each panelboard.

Although the NEC doesn’t require a specific color code for ungrounded conductors, electricians often use the following color system for power and lighting conductor identification:
• 120/240V, single-phase—black, red, and white
• 120/208V, three-phase—black, red, blue, and white
• 120/240V, three-phase—black, orange, blue, and white
• 277/480V, three-phase—brown, orange, yellow, and gray; or, brown, purple, yellow, and gray

Avoiding feeder problems
The NEC provides the minimum size a feeder must be. It also recommends upsizing your conductors for voltage drop. But there are many other factors to consider for a successful feeder installation, including selecting an insulation appropriate for the application and environment.