Looking to replace my old transformer with a new 120V to 16V transformer to power a new smart doorbell. The new transformer has standard white, black, and green wires. Old transformer only had white and black.

The wiring of the old transformer confuses me. Here's a picture of the wires in the junction box: https://imgur.com/a/WkJNG9C

enter image description here

  • All 3 of the whites were pigtailed to the old transformer white.
  • The black was pigtailed to the old transformer black.
  • The 2 reds were not wired to anything?!
  • The ground was not wired (old transformer has no ground)

How do I safely wire my new transformer?


I have a handyman with electrical experience looking into it right now. Here are some updates photos of interior: https://imgur.com/a/9VOzOqO

If the whites were all joined before, your detector is probably giving a false reading on the one it thinks is hot.

Actually, that white is just hot hot. Hopefully this guy can wire it up safely. He's going to be installing an actual electrical box inside the wall to hold all of the wires, which I believe a few of y'all said should be done. I'm not sure what he's planning on doing about the hot white - for now he's just put a cap on it.

  • With my death stick voltage tester: The top red wire is hot, and one of the white wires is hot. May 28, 2023 at 14:21
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    Usually the recommendation is to wire the new as the old one was. Ground is just for your safety, so ground to ground. The problem is with the extra wires. White should always be paired with a black or a black and red. Two extra whites and two reds without two blacks is odd(except for conduit, which you do not seem to have).
    – crip659
    May 28, 2023 at 15:19
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    First for safety sake, consider a new junction box. what you have is a box extension .
    – RMDman
    May 28, 2023 at 15:31
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    Will need to take that (code-violating fire-hazard) mess apart and see what's going on behind it. Is there a box buried back there with some wires "lost to view?" Seems likely as no cables come into the visible box extension from there, but wires do. In any case, it needs to be fixed. If the whites were all joined before, your detector is probably giving a false reading on the one it thinks is hot.
    – Ecnerwal
    May 28, 2023 at 19:44
  • Thanks for the responses. I've gotten a few different quotes from handymen & electricians: one for $200 and one for $400. $400 seems high... but I'm not sure. I want this fixed right. What ballpark should I expect? Or tough to provide an accurate quote without more info? May 28, 2023 at 19:48

1 Answer 1


I can tell from the drywall work that this isn't a "finished" space in the home. And they were kind enough to screw down that board, so I would de-energize this stuff and take it apart and see what's behind it.

I'm guessing maybe the last guy did that abortion with the wood because they had a 4"* octagon box extension box, but the box in the wall was 4x4 or a Handy-Box. If so, great - we can just get a 4x4 extension either for 4x4 or for Handy-Box, and mount the transformer on the 4x4 lid or on a side KO.

If it's just a bunch of cables flopping around, then we would need a box big enough to land all the cables in appropriate cable clamps (e.g. there are cable clamps into a 1/2" knockout for almost any wire type) and then mount the box physically. Then the transformer can go on the lid or a knockout.

* And what the BLEEP is up with octagon box sizes? You notice they have "major sides" and then "corner clips" like paper on Battlestar Galactica (2004). To get the actual trade size, you have to measure across the diagonal "corner-clips". You will get 3-1/2" or 4", which are box sizes (4" is far more common). If you measure across the flats, the measurement will be 1/2" shy of correct. That's an easy way to get 3-1/2 and 4" boxes confused.

  • Thanks for the answer. Also, there's no box in the wall - see my update on my original question. I have a handyman installing a new box right now. May 29, 2023 at 19:22

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