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I am hoping to install zooz smart switches, however the instructions state "14AWG wires only!", but I have a 20amp circuit which uses 12awg wire. Looking at the code regarding smart switches:

"They shall be marked by their manufacturer with their current and voltage ratings and used for loads that do not exceed their ampere rating at the voltage applied."

The switches will be connected to ceiling fans and lights, none of which will draw more than 15amps or exceed the other limits set by manufacturer, so it is my understanding that using these switches is allowed on a 20amp circuit, but practically it seems that:

A) I shouldn't use these switches on 20amp circuits, as I'm not sure how one could without either using 14awg wire on 20amp circuit, or ignoring the manufacturer's instruction with the exclamation mark to only use 14awg wire.

B) I could disregard the manufacturers statement about only using only 14awg wire. I'm not sure why 12awg would cause an issue, the switch is only rated for 15amps, but 14awg wire would not prevent a load of more than 15amps, correct?

C) I could pigtail 14awg wire to the 12awg wire in my junction box, but I believe doing so is against code and generally considered bad, and therefore I'd rather not, although I'm not quite sure why in this scenario:

  • the light fixtures/fans themselves have 16awg wires, if there was a scenario where 18amps was going to the fixture, would not these wires be at greater risk of combusting than 14awg jumper wires?
  • the circuit powers multiple light fixtures, two ceiling fans, and 8 outlets plugged to speaker system and small kitchen appliances, it seems unlikely that a rogue smart light or something would be able to draw more than 15amps without tripping the circuit.
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  • The breaker protects the wire. 14 gauge wire allow 40/50/or more amps to flow though it, getting very hot/red hot lighting close by things on fire. you must follow manufacturers instructions to be in code. You cannot have 14 gauge wire on a 20 amp circuit, unless the manufacturers supply it. Might be time to look for different smart switches.
    – crip659
    Sep 27 at 22:20
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    Wow! I verified with one of the manuals. It looks like rather than backstabs (bad, but very much specific to a particular size, and normally only 14 AWG, which would at least make sense) or traditional loop around screws or typical "screw to clamp", they use a very peculiar screw to clamp sort of that apparently is specific to 14 AWG. That is really poor design, IMHO.
    – manassehkatz-Moving 2 Codidact
    Sep 27 at 22:26
  • Where were you able to see that these kind of clamp screws can only use 14awg wire? It crossed my mind that somehow the terminal screw mechanism was why it said "14 awg only", but it seemed like a very stupid and avoidable design flaw, and that clamping a piece of wire down with a screw should work for 12/14awg
    – user8340913
    Sep 27 at 22:44
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    This limit is a bad one. Yet it exists.
    – manassehkatz-Moving 2 Codidact
    Sep 27 at 23:06
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    99% of the time you must obey what the manufacturer says in their instructions, even if code says something else. If manufacturer says to connect their 18 gauge to your 4 gauge(not 14 gauge) that is what you do. What the manufacturer says usually overrides code.
    – crip659
    Sep 27 at 23:08

2 Answers 2

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You can totally use 15A rated switches on a 20A circuit, provided they have a fixed load of 15A or less on them. What you can't do is hook up 14 gauge wire in a 20A circuit, even if it's on the other side of a switch. Since these switches don't work with any wire bigger than 14 gauge, they won't work for your scenario. This means you have two choices:

  1. Select smart switches that are rated for 20A circuits / to go on 12 gauge wire. They exist. In fact these Zooz ones seem to be an exception. Most smart switches have pigtails that you can connect to 12 gauge wire with wire connectors. Yes, these pigtails are probably not 12 gauge, but it's okay for Reasons (i.e. it's okay because the manufacturer went through testing in the appropriate scenarios).
  2. Change out the breaker from 20A to 15A, permanently derating the whole circuit to 15A. If it's a kitchen circuit this might not be allowed.

Any other options may be fine, may not be. We can't really say as we're not a NRTL and haven't done the testing to know if it is or isn't appropriate to use these devices on a 20A circuit. Companies like your light fixture manufacturer have done the testing that is appropriate to ensure that they can use 16ga wire. Zooz has apparently decided to just forego the whole thing and say 14ga / 15A circuit only. Believe the manufacturer. Don't try to hack around things.

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  • Thanks, I'm going to return them, but is the issue with 12awg just a factor of the terminal screw design? Tbh I have a hard time believing that if I just wrapped 12awg and tightened these screws that there would be any real risk of one coming loose, and if there was, the manufacturer should probably be required to make it much more clear than a single line in the instructions that one could easily glance over.
    – user8340913
    Sep 27 at 23:40
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    I can't tell you why they put that restriction in place, just that it is there. You don't get to ignore the instructions, and you can't add 14ga pigtails to your existing wires to work around them. So there you are.
    – KMJ
    Sep 28 at 0:32
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I found the same 14 gauge requirement in the instructions for a couple of Zooz switches. One of them provided a little more information: Do not insert 12 AWG wires into the terminals - this switch is rated for 15A only and should be wired with 14 AWG wires only.

It looks like the issue is that their switches are not approved for 20 A circuits.

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    As I understand it, a 15A switch (i.e., not designed to switch more than 15A safely) can be a part of a 20A circuit, provided it is designed in such a way that it won't actually switch more than 15A. And in fact many smart/dimmer/etc. switches have for a long time had limits, often far below 15A (e.g., 600W of one type of light, 300W of another, etc.) So it is likely that they could make this work in a 20A circuit with 12 AWG wire, but for whatever reason they chose not to do so. Poor design.
    – manassehkatz-Moving 2 Codidact
    Sep 28 at 1:06
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    @manassehkatz-Moving2Codidact: I don't that it has ever been proper to install on a 20A circuit a switch that could fail in such a way as to cause a fire hazard if overloaded in a manner that wouldn't trip a 20A circuit breaker. Switches may suffer irreparable damage from lower currents, but only if they wouldn't pose a fire hazard.
    – supercat
    Nov 27 at 20:15

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