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 don’t have feeder circuits.

Here’s an object lesson in the value of Article 100. Go there now and review the definitions of branch circuit and feeder circuit. Once you’ve done that, you will understand why Article 215 is so much shorter than Article 210.

1. 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.
    
2. 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).
    
3. 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)].
    
4. 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.
    
5. Size your feeder overcurrent protection per Article 240 [215.3]. This protection isn't optional.
   
6. 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].
   
7. 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].
    
8. 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].
    
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].
   
10. 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].