I just bought a house and there are two transformers in the garage. I'm trying to figure out what they do. The house was built in 2014 and located in San Mateo, California.

I suspect one of them is for the doorbell (since there must be a doorbell transformer somewhere). I'm guessing it's the one with two cables (one for the button and one for the chime).

I have no idea what the other one (the one with yellow tape) is for. What I do know is that it is hot, so it must be powering something. (The blue one is slightly warm, but definitely not hot.) Any idea what this could be for? It's not for the alarm system (I already identified the alarm system's transformer) and I don't think it's for the furnace, since it is not nearby.

I'm also not sure how to disconnect either of these transformers. At first I thought it was an ordinary outlet/plug. I pulled and it didn't come out. Then I noticed that it can twist. What kind of connection is this? and how do I "unplug" them?

I'm going to try disconnecting the wires to see what stops working. But I need to turn it off first via the circuit breaker. How do I verify that it has been disconnected since there is no direct indication that it is or is not connected?

transformer with 3 cablestransformer with 2 cables

UPDATE: I got a multimeter. The one with yellow tape and 3 cables is 14.7VAC and the blue one with 2 cables is 20.2VAC. I identified the correct breaker, but it also took out the lighting in the garage…

  • Do you have a voltmeter with an AC setting? May 25, 2021 at 1:34
  • @Harper-ReinstateMonica I just ordered one.:-)
    – Thomas
    May 25, 2021 at 1:39
  • I bet they are both 16v transformers and the blue one isn't hooked to anything anymore.
    – dandavis
    May 25, 2021 at 6:22
  • @dandavis Second one could power an always on low-voltage circuit somewhere. Could even be a doorbell (with the button having separate wires going to the buzzer).
    – Tonny
    May 25, 2021 at 14:01
  • These transformers are more than meets the eye!
    – RonJohn
    May 25, 2021 at 14:44

1 Answer 1


One of them (top picture) is your door bell, and the second one could be the garage opener, sprinkler controller, or low voltage lighting of some sort. Typically, there is an electrical box behind it and it is 120v. You can use ether multi-meter or electrical tester like this to determent if the wires are hot or not and shut one breaker at the time. Sometime there might be a label in your service panel for those.

  • Since there are 3 cables going to the top one I would guess a door-bell with 2 buttons (are there 2 doors or a drive-way gate and a door ?) or a single button door-bell that rings 2 buzzers.
    – Tonny
    May 25, 2021 at 13:58
  • @Tonny there's only one doorbell button that I am aware of. The only entrances are the front door and the garage.
    – Thomas
    May 25, 2021 at 16:35
  • I've never seen a garage door opener that needed a separate transformer like that, and this would be an odd place indeed to mount a transformer for a sprinkler control. Low voltage lighting I could see. Maybe...
    – FreeMan
    May 25, 2021 at 18:12
  • Garage door probably would have it's own power supply/transformer build in but sprinkler controller, if the low voltage wires for the valves are in the garage (mine are), it is very possible to have it there. It's very hard to tell by the provided pictures where exactly they are located
    – IgorK
    May 25, 2021 at 19:05

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.