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I am attempting to replace my doorbell transformer with one that will provide adequate voltage for my ring doorbell. I have located the current transformer but the wiring does not seem to match my instructions. The instructions for the transformer I want to install tell me to connect the black, white, and green wires individually to their matching wires with a wire nut. The existing transformer has the black wire attached directly to the box, and the white and green are attached together with a grey/brown wire (so 1 green, 1 white, and one grey/brown connected via wire nut). It looks like the grey/brown wire is connected to the ground bar. enter image description here

Would it be okay to connect my new transformer the same way?

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  • you should have only two wires going to the door bell. What are they
    – Traveler
    Jul 31, 2022 at 4:32
  • Picture of the current transformer and wiring would help. Jul 31, 2022 at 4:51
  • Thank you, I just added a picture.
    – Lex
    Jul 31, 2022 at 5:32

2 Answers 2

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This is a hack job install. Who ever did this put 2 wires under one screw (not good and not code legal), then they wire nutted the ground and neutral, which ends up using the metal of the panel itself as the neutral! Bad idea. The way to correct is to move the white wire to a neutral/grounding buss bar, you can ignore (cap off) the green wire since the transformer is already grounded via its mounting to the panel. If you want to be picky, just connect the green wire to the grounding buss bar as well. You should also pig tail the 2 hots under one screw to make it code legal.

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The green (ground) connection to the grey (presumably neutral) is wrong, just like any neutral-ground bond anywhere other than the main panel. If the grey wire were to slip out of the wirenut, the body of the transformer would rise to 120 volts (hot, through the transformer primary to the white wire to the green wire) and could electrocute someone!

Look for a wire, or a bundle of wires, either bare, green or green/yellow. This is the ground. Connect the transformer green wire to that (If a bundle, add the new wire to the wirenut, don't separate the existing wires).

If there are not such wire(s) in the box and the box is metal, you should connect the green wire to the box. There should be a screw hole tapped for a 10-32 screw. Use a 10-32 x 3/8" machine screw to secure the wire to the box. You may already see a screw securing the existing ground wire: do not remove it. Look for another suitable hole/screw.

If the box is plastic and there is no sign of a ground wire in the box, just put a small wirenut over the end of the green wire and tuck it into the box.

Edit based on the photo and additional information:

I see several problems now. Whoever installed the old transformer cheated quite a bit. First, the transformer black wire connected along with another wire to the breaker ( it's generally not allowed to put two wires under a screw). Second, even though white and green wires are being connected to the ground/neutral bus, you still aren't allowed to use a single wire to connect these.

Disconnect both wires from the breaker and add a short length of #14 black wire as a pigtail. Connect one end to the breaker and connect the other end to the other two wires with a wirenut.

Disconnect the transformer green wire from the grey wire and use another pigtail (green) between it and the ground/neutral bus. also, if the grey wire is smaller than 14 gause, you should replace it with a #14 white pigtail.

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  • Just for some additional context, the transformer is sitting on top of my braker box, I added a picture for reference. The greyish brown wire seems to be connected to the ground bar. so I would assume the green wire being connected to the grey/brown wire is correct. the question is what to do with the white wire?
    – Lex
    Jul 31, 2022 at 5:35
  • @Lex Please see my edits.
    – DoxyLover
    Jul 31, 2022 at 5:54
  • thank you but I am still unclear on what to do with the white wire? are you saying they should both be connected to the ground bar but not connected with the same pigtail?
    – Lex
    Jul 31, 2022 at 6:03
  • @Lex That is correct. The problem with a single pigtail is that if the pigtail fails, the case of the transformer could be energized, hot, through transformer, to neutral to green (ground) wire to case. With separate pigtails, if one fails, that wire is simply disconnected.
    – DoxyLover
    Jul 31, 2022 at 7:10
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    @GeorgeAnderson I was assuming that the transformer body might not be making good contact to the panel case. Actually, the breaker wouldn’t trip. Instead, the neutral current would flow through the case. In any case, I still contend this is not much better than an outlet with a bootleg ground.
    – DoxyLover
    Jul 31, 2022 at 15:33

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