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I am working on a wiring project at my home, and I have a specific question about whether something I am doing is advisable or allowed by the NEC.

Background

I have a branch circuit with a 20 A breaker and 12 gauge wire throughout. It feeds a 20 A GFCI duplex outlet in the garage. Downstream from the GFCI is a 15 A duplex outlet outside near the eaves of the house, serving as a connection point for Christmas lights. Both receptacles in this 15 A duplex outlet are controlled by a 15 A smart switch inside the home.

The Problem

I am concerned about both receptacles in the 15 A duplex outlet being controlled by a 15 A switch while on 20 A branch circuit. I know not to overload the switched receptacles beyond 15 A, but I have no guarantee that anyone in the future will know that. What if someone loads up one receptacle to 12 A and then the other to 5 A? Then the switch would have 17 A through it, exceeding its rating, without tripping the breaker. Perhaps I am misunderstanding; is the maximum rated current for a 15 A duplex outlet 15 A total, or 15 A per receptacle? If it's per receptacle, then I am in trouble. I think a solution, if this is the case, would be to have only one of the receptacles in the 15 A duplex outlet controlled by the switch.

My Question

Is it acceptable to use a 15 A switch to control both receptacles in a 15 A duplex outlet on a branch circuit with a 20 A breaker?

https://i.imgur.com/v2lHftJ.png

circuit diagram

  • Wow! Well done, you kept all your neutrals properly segregated without marking. That is skill we're not used to seeing here. Just the same it helps to mark wires to show they are distinct. I use colored tape for that purpose. – Harper Dec 22 '17 at 21:05
  • Standard duplex receptacles usually carry a 20amp rating for the contacts, but have a NEMA 5-15 duplex face. As far as the smart switch, you’d need to give us the specific model number. For example, Insteon has switches where the switched or dimmed load is rated less, 600w, 1000w, 15amp, however all devices have #12 pigtail leads and can be used on a 20amp circuit. – Tyson Dec 22 '17 at 23:24
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Nope -- swap to a single receptacle

You cannot do this, as you could plug two 12A loads into the switched duplex receptacle and overload it. Oops!

In the Code, this is written up in NEC 404.14(F) (informational note omitted as it's irrelevant to the topic at hand):

(F) Cord- and Plug-Connected Loads. Where a snap switch is used to control cord- and plug-connected equipment on a general-purpose branch circuit, each snap switch controlling receptacle outlets or cord connectors that are supplied by permanently connected cord pendants shall be rated at not less than the rating of the maximum permitted ampere rating or setting of the overcurrent device protecting the receptacles or cord connectors, as provided in 210.21(B).

Exception: Where a snap switch is used to control not more than one receptacle on a branch circuit. the switch shall be permitted to be rated at not less than the rating of the receptacle.

Switching to a single receptacle (one receptacle on the yoke vs a duplex receptacle i.e. two receptacles on a single yoke) for the holiday-lights receptacle puts you under the Exception though, which makes this all hunky-dory provided the switch is rated to the full 15A (1800W) that can be pulled from the receptacle.

  • Thank you! This is exactly the type of answer I was looking for! – Kyle U. Dec 23 '17 at 0:11
  • What do these 15-A smart switches do if the loads cause them to carry current above 15 A? Do they trip off? Perhaps the cited section of code refers to an ordinary snap switch? Do these smart switches come with a 20-A rating? I suppose if they exist, 20-A models would be much more expensive. – Jim Stewart Dec 23 '17 at 0:14
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    @JimStewart -- you can't plug a >15A device into a 15A receptacle to begin with. Beyond that, it's assumed the breaker will trip if the circuit is grossly overloaded. – ThreePhaseEel Dec 23 '17 at 0:51
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    @JimStewart - These 15 A switches do not have overcurrent protection. Say you were to overload the 15 A switched receptacle by daisy-chaining a large amount of holiday lights. If this load were over 15 A but under 20 A, you would be creating a dangerous situation since the switch and receptacle are only rated at 15 A, but overcurrent protection is at 20 A. This problem exists if you switch a single receptacle, or a duplex. But as ThreePhaseEel pointed out, switching a single receptacle is to code, but a duplex is not. I have looked for 20 A smart switches, but have been unsuccessful thus far. – Kyle U. Dec 23 '17 at 5:37
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    @JimStewart - I think it would be to code if you have one of the receptacles switched and one of the receptacles "always on". This way you would avoid having a disconnected receptacle that does nothing. I am in a dilemma right now as to whether I want to go with the duplex outlet (one receptacle switched, one always on) or a single outlet. It was easy enough to find the single outlet - my local Home Depot carried them. Since this outlet is located at the eaves of my home and I need a ladder to get to it, I believe having one receptacle that is not switched may be of questionable usefulness. – Kyle U. Dec 24 '17 at 0:58

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