National Electrical Code Articles and Information
National Electrical Code Tips:
Article 215 -- Feeder Circuits
by Mark Lamendola
Based on the 2023 NEC
Please note, we do quote from copyrighted material. While the NFPA
does allow such quotes, it does so only for the purposes of education
regarding the National Electrical Code. This article is not a substitute
for the NEC.
One thing that jumps right out to people studying the NEC is that
Article 215 is very short. This is surprising to people who've
just studied Article 210, Branch Circuits, and are moving on to the next
logical step. You might be thinking feeders are just a heavy version of branch
circuits, so Article 215 should just be Article 210 on steroids. But,
don't think that way because "it aint so."
Article 210 covers many permutations of branch circuits, and devotes
extensive text to dwelling area branch circuits. Dwelling areas donít
have feeder circuits.
Hereís an object lesson in the value of Article 100. Go there now
and review the definitions of branch circuit and feeder circuit. Once
youíve done that, you will understand why Article 215 is so much
shorter than Article 210.
Article 215 covers feeders, but it doesn't cover feeders over 1000VAC or over 1500 VDC [215.1]. As of the 2023 revision, those are covered in (new with 2023) Article 235.
- To size the feeder correctly, you must first determine the total load
[215.2(A)(1) and (2)]. To do that, follow the calculation requirements of Article
220. You can find good feeder calculation examples in Informative Annex D. Work your way through Examples D3 and D3(a).
- The grounded conductor (which is usually, but not always, the neutral)
must be sized at least as large as required by 250.122 [215.2(B)].
- The feeder ampacity has to be at least that of the service conductors,
if the feeder conductors carry the total load of the service conductors with
an ampacity of 55A or less [215.2(C)]. Since individual dwelling units typically have a 200A service these days, 215.2(C) (it was 215.2(A)(3) in the 2020 NEC) already covers this. Back in the 1950s and earlier, homes were built with a 30A service. It's been a long time since 60A was normal, so the 55A rule excludes single family residential homes. But what about apartments? Even for small flats in a building without individual air conditioning units, we're typically above 100A. There's an electric range hookup, garbage disposal, and refrigerator. There are also receptacles for small appliances, plus modern lighting. You're just not going to see anyone build a residential unit with a service under 55A today.
- Size your feeder overcurrent protection per Article 240 [215.3]. This protection isn't optional.
- Up to three sets of 3-wire feeders or two sets of 4-wire or 5-wire feeders can use a common neutral [215.4].
- If the feeder supplies branch circuits in which equipment grounding
conductors are required (and usually, they are), then the feeder must also
include (or provide) an equipment grounding conductor [215.6].
- Feeders that supply 15A and 20A receptacle branch circuits can be
protected by a ground-fault circuit interrupter instead of complying with
210.8 and 590.6(A) [215.9].
- Don't derive feeders from autotransformers unless the system supplied by
the feeder has a grounded conductor that's electrically connected to a
grounded conductor of the system supplying the autotransformer [215.11].
- Surge protection in the form of a surge-protective device (SPD) must be installed on any feeder that supplies any of the four occupancies listed in 215.18(A). For example, they must be installed on any feeder serving a dwelling unit. And it has to be a Type 1 or Type 2 SPD [215.18].