I'm replacing an old doorbell transformer. After removing the junction box, I have 3 exposed black wires. I have the new transformer with the typical White, Black, Green wiring, but I don't know which wires - if any - to connect the green. I added a photo. Any help would be appreciated.enter image description here

  • I can't tell on the old stuff whether green is discoloration of some sort or green insulation == ground wire. But on any new device with black/white green, the green wire should be ground and connected to other grounds and/or (if you have a metal box and metal conduit that is part of the grounding system) screwed to the box. Sep 3, 2018 at 19:57
  • The wires are in terrible shape. The green you see there is some sort or erosion. My old transformer doesn't have the ground wire. Assuming that means the box is grounded? Could I cap off the ground and wire bolt the like colors together? Some of my questions may come off ignorant, first go round with electrical work here.
    – Billy
    Sep 3, 2018 at 20:08
  • If the box is grounded then any ground wires should be screwed to the box. Wire nutting like colors together is generally the right thing to do, but there can be exceptions. In addition to the corrosion, I'm concerned about the existing bunch of white (presumably neutrals) taped together - if they are simply twisted together under the tape instead of nutted then they should get a proper wire nut. Sep 3, 2018 at 20:20
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    How about vacuuming/cleaning all the crud out of the box so you can see what you're looking at? The condition of some of those wires looks dangerous, and may need some more attention to be rendered safe, but you can't see to tell. Was this box covered with insulation? Sep 3, 2018 at 20:57
  • It was, yes. Sorry, the pic was taken immediately after removing the junction box.
    – Billy
    Sep 3, 2018 at 21:10

1 Answer 1


The bare grounds are buried in the bottom of the box there

Since these are NM-type cables we're dealing with here, the ground wires in the box will be bare wires, and lo and behold, there's a whole bundle of them improperly spliced together in the bottom of the box. Take a suitably sized wirenut and nut the green wire on your transformer to that bundle of bare wires (this will also properly splice the bare grounds to each other).

As to the hots and neutrals

The black wires in this box are all hot, and the white wires are all neutral (otherwise, there'd be a white spliced to something that isn't white, that's a clue that shenanigans are afoot). So, in this case, it's black nutted to black, white nutted with whites (and you may wish to replace the splice of the existing neutrals with a proper one while you're at it), and grounds as above.

  • Appreciate the help. I see the wires you are talking about. I went to check the breaker box before going back up to the attic to connect the new transformer. Looks like whatever I did yesterday, tripped the breaker and it won't go to the on position. What is the correct wiring here - outside of the already mentioned ground to the bundle on the bottom - Am I connecting the 3 blacks + the black from the new transformer all in one nut? Again, thanks for the advice.
    – Billy
    Sep 3, 2018 at 21:02

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