National Electrical Code Tips: Article 215 -- Feeder Circuits

by Mark Lamendola

Based on the 2020 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 not feeders for electrolytic cells [215.1]. Those are covered in 668.3.
    
2. To size the feeder correctly, you must first determine the total load [215.2(A)(1)]. To do that, follow the calculation requirements of Article 220.
    
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(A)(2)].
    
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(A)(3)].
    
5. The 2020 NEC removed this requirement: "Feeder conductors to individual dwelling units don't need to be larger than the service conductors [215.2(A)(4)]." So where does that leave us? Since indidividual dwelling units typically have a 200A service these days, 215.2(A)(3) 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.
    
6. If supplying only transformers, the ampacity of feeder conductors over 600V must be at least the sum of the nameplate ratings of the transformers [215.2(B)(2)].
    
7. Size your feeder overcurrent protection per Article 240 [215.3]. This protection isn't optional.
    
8. 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].
    
9. 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].
    
10. 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].