While hooking up a series of LED ceiling lights, I was wondering if there is anything in the NEC that would prohibit circuits smaller than the standard 15A lighting circuit found in homes.

This 15A lighting circuit currently feeds 8 ceiling lamps, but I could wire up 20 of these 11W LED lamps and still only use 2 amps which would easily run on a 5A circuit and use 18 or maybe even 20 gauge wire.

I haven't seen any home wiring supplies for anything less than 15A, but I don't know if that's because there's no demand, or if 15A is the smallest lighting circuit allowed by the NEC.

Or is there some burgeoning low voltage, low power standard that is better suited to energy efficient lighting?

  • You can absolutely run 18 gauge to all your LED lights provided you have the transformer supplied with a 14 gauge or larger.
    – Kris
    Aug 20 '15 at 20:42
  • I've seen prefabricated "shacks" that were wired with #16. Whether or not this is common practice I don't know
    – Kris
    Aug 21 '15 at 0:58
  • Just clarifying a bit (helpfully, I hope), @Kris is saying that if your lights are low-voltage, powered by a transformer, the rules are different than if you were running 120V to each light canister. In which case you could run #14 to the transformer, terminate that appropriately, then run smaller low-voltage wire to your lights. But if your lights all have transformers built-in and require a 120V connection to each fixture, you have to run at least a 15A circuit, which requires at least #14 wire. Aug 21 '15 at 23:59
  • @Craig. Yes that's what I meant. Thanks for clarifying. And indeed #18 would just be for very short runs at the risk of voltage drop being an issue.
    – Kris
    Aug 22 '15 at 1:05

It looks like the NEC allows only specific circuit ratings. From the 2014 NEC:

210.3 Rating
Branch circuits recognized by this article shall be rated in accordance with the maximum permitted ampere rating or setting of the overcurrent device. The rating for other than individual branch circuits shall be 15, 20, 30, 40, and 50 amperes. Where conductors of higher ampacity are used for any reason, the ampere rating or setting of the specified overcurrent device shall determine the circuit rating.

The exception specified is if the circuit supplies only a specific item, an "individual branch circuit":

Branch Circuit, Individual. A branch circuit that supplies only one utilization equipment.

There are also some other exceptions that don't apply here, like for motor loads and in industrial settings.

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