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I am replacing my very old doorbell transformer to adequately power my new video doorbell. The new transformer has a black, white, and green wire. However, the outlet/box it will be connected to only has a red and white wire. The old transformer only had two black wires. One is connected to the red wire and the other to the white wire. I've read and seen videos that a red wire is the the same as black, they're the hot/live wires. If so, those are a match and can connect them. And I can connect the white wire on the new transformer with the white on the outlet/box. But what do I do with the green wire from the transformer?

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    In North America, red is also a hot wire colour. Green wire will be connected to the metal box with a screw. The green/ground wire might not do anything if the box itself is not grounded, but is for your safety only/not needed to make the circuit work.
    – crip659
    Commented Apr 27 at 15:50

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There are more connections that you haven't noticed. Some might be screw terminals rather than wire leads.

The new transformer has black, white, and green leads. These are for connection to the 120 volt mains supply. It also (most likely) has screw terminals. These are for connection to the doorbell circuit. Your red and white wires, especially if they are very thin, are most likely to be the doorbell circuit wires and should connect to the screw terminals. Order doesn't matter; either red or white can go to either screw.

Is the old transformer mounted to the side of the junction box? It's likely that the mains supply wires of the old transformer exit through that mounting point and connect to thicker building wires which are the 120 volt supply. The black and white wires of the new transformer would connect to those. The green wire of the new transformer should connect to an earth/ground, which might be a bare copper wire in the mains supply cable.

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