I have a 15 amp breaker that’s used for my foyer/family room. The builders double tapped that breaker to add a 16V-10VA transformer for the doorbell to the side of the service panel via a knockout. See pics below.

I plan to swap the existing transformer with a 16V-30VA transformer to power a Unifi G4 Doorbell along with my NuTone chime box. In the process, I’d like to correct the double tap.

My question is: Do I need to worry about the wire gauge of the transformer wires if I wanted to correct the double tap via a pigtail? The AWG of the transformer is 18. As far as I know, this is not up to for code for a 15 amp circuit. Is it ok if I proceed to pigtail with the mismatched wire gauges? I understand the current transformer is also a different gauge wire and double tapped which seems to work fine, but I’d like to correct it.

My other question is: Instead of a pigtail, if I were to add another single pole 15 amp breaker to correct the double tap, would I need to worry about the wire gauge of the transformer as long as the doorbell is the only thing on that breaker?

Finally, I know it’s “common practice” to double tap for doorbell transformers, so how bad is it really if I didn’t fix the double tap?

I’m not so concerned about being perfectly up to code. Instead, I’m looking for something that is safe and reliable.


Pic of double tap Pic of panel and transformer

  • Am I the only one horrified that there is a bare metal connector in the panel on a 120v hot connector? – FreeMan Dec 11 '20 at 12:05
  • @FreeMan are you talking about the aluminum neutral wire coming from the service drop on the right of the picture? It is my understanding that this is “allowed” by code? – thehin Dec 11 '20 at 16:17
  • No, I'm talking about the metal connector on the black, hot, wire just below your circle. – FreeMan Dec 13 '20 at 13:07
  • Oh, the pic quality is poor. That’s just a quick wire connector that I guess the builder/electrician used when installing. It’s not actually touching. Here are better pics: s3-eu-west-1.amazonaws.com/cdn.pbrd.co/images/JETTgwt.jpg?o=1 | s3-eu-west-1.amazonaws.com/cdn.pbrd.co/images/JETUx3o.jpg?o=1 – thehin Dec 14 '20 at 15:12
  • A) I don't see additional pics. B) Even though it's not touching now, it could touch something when someone is working in there, or it could touch the cover when installed, energizing the cover. Guess I'm the only one concerned about it... – FreeMan Dec 14 '20 at 15:16

The leads for the transformer are sized per the NRTL Listing, don't worry about that.

Those breakers aren't listed for double taps, the fine print on the breaker will tell you if they are.

Minor violation being tapped to dining receptacle circuit. NEC 210.52(B)(1) includes dining area receptacles in the scope of the two or more 20A circuits that serve kitchen receptacles, and 210.52(B)(2) says they shall have no other outlets. (Hardwired connections are included in the definition of outlet.)

Probably not much you can do about a 15A serving dining area, but just add a 15A breaker, spare spaces are near the transformer, and much tidier than splices.

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    I just double checked..the double tap is using the breaker for the foyer/family room (not the dining room). So I will most likely add a single breaker and directly connect the transformer. If I ever need more space, I’ll pigtail. As @NoSparksPlease eluded to, looks tidier :-). I will be sure to post pics after I’m done. – thehin Dec 11 '20 at 6:18

Just fix this with a pigtail + wirenut

Your breakers are GE breakers that do not support a "double tap" connection. Fortunately, this is easy to fix; since this a 15A breaker, a length of 14AWG THHN and a wirenut suitable for the wires involved can be used to combine the new pigtail with the existing branch-circuit and transformer hot wires, while the other end of that pigtail simply lands on the existing breaker hot terminal. Make sure to do this with the breaker in question turned OFF, of course, and you'll want to use an inch-pound torque screwdriver to torque the breaker and neutral screws to spec, as well as cranking that wirenut down tight!

  • Thanks! Does it matter that the gauge of the transformer wire is 18 AWG? Also, since I have the free breaker slots, is it fine to add a new breaker dedicated to the transformer? Same question, does it matter what gauge the wiring of the transformer is if I use a dedicated breaker? I would simply connect the transformer hot wire directly to the breaker if I went that route. – thehin Dec 11 '20 at 2:49
  • @thehin -- it doesn't matter that the transformer itself uses 18AWG leads as those are covered by the UL/... listing on the transformer, and there's absolutely no need to bother with wasting a breaker space on a doorbell transformer – ThreePhaseEel Dec 11 '20 at 2:50
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    @thehin -- the transformer wires would be fine since they're only carrying the current the transformer is drawing, which UL assures us can't be too much – ThreePhaseEel Dec 11 '20 at 2:58
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    @thehin The key, which is standard/code for normal wiring, is that the transformer and the other loads are in a tree topology. That is the case whether double-tap or pigtail or actually pretty much any legal wiring scheme you can think of. With a tree, each wire only carries current for the following loads, not the entire load (with the exception of the first branch coming out of the breaker). If you were to wire things up serially instead of as a tree then that 18 AWG wire would be a problem - but you would have lots of other problems as well - that would be the least of them! – manassehkatz-Moving 2 Codidact Dec 11 '20 at 3:08
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    @thehin please say "thanks" by clicking the up arrow next to any and all answers that you found helpful. Also, click the check mark next to the answer that you found most helpful. – FreeMan Dec 11 '20 at 12:06

Double-tapping is not a problem, provided the breaker in question allows it (check the documentation) and you local AHJ hasn't specifically prohibited it.

The correct way to double-tap is to use 2 of the same gauge wires. Your builders appear to have done the right thing: they used the same type of wire as the one already on the breaker, and then used a (I presume) rated device to go from that to the transformer wire. A simple wire nut would have also been acceptable.

In your case, I would probably just re-use what it already there, or perhaps replace it with a wire nut.

  • Thanks for the response! I’m curious, how can you tell that the builder used the same gauge wire? – thehin Dec 11 '20 at 2:31

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