Old doorbell transformer wired directly into electrical box, don’t know how to disconnect without cutting the wires?

Question

Total amateur here. I’ve watched multiple video tutorials on replacing an old doorbell transformer with a new one, and none seem to address my particular set-up.

My old transformer is attached to the breaker panel. The first point of confusion is that the old transformer has only two black wires coming out of it, which doesn’t match the video tutorials showing three wires so it’s unclear to me how to attach the 3 wires coming out of the new transformer (green, white, black) I purchased because I cannot match them up with the existing set-up.

Second point of confusion is I can’t figure out how to detach the old transformer because the wires run directly from inside the old transformer to (1) a breaker switch inside the panel and (2) to a metal part inside the panel. The tutorials I watched showed wire nuts holding the connection from the old transformer, and it’s a simple matter of unscrewing the wire nuts and attaching the new transformer via the same wire nuts. But there are no wire nuts here. Am I supposed to cut the two black wires to remove the old transformer?

Answer 1

The most common setup is a junction box with wire nuts. However, in your case the original installer did a mostly good thing by installing it on the panel. The only bad part, in my opinion, is that they left the black wire as is (didn't mark it to indicate neutral, which is normally white).

Removal is easy:

• Turn off the breaker
• Remove the low-voltage wires (probably screw terminals, but can't see) from the transformer
• Loosen the screw on the breaker and remove the hot wire
• Loosen the screw on the neutral bar and remove the neutral wire
• Remove the transformer from the panel

For the new transformer, you do the above in reverse. For the wiring:

• Black to breaker
• White to neutral bar
• Green to ground bar or neutral bar. You can't always put grounds on the neutral bar, but since there are already many grounds on the neutral bar, it is presumably a true main panel where that is allowed.

Your existing transformer is grounded by contact with the panel. Your new one will most likely be grounded that way as well. The green wire is provided to make sure it is grounded in case it is installed on a plastic box. However, unless the new transformer directions say that the green wire does not need to be connected when used with a grounded metal box, you should still connect the green wire.

Note that typically you can put multiple ground wires under a single screw but not multiple neutral wires. Check the panel label. I think yours is similar to mine (definitely same brand based on breaker handle color), in which case you can put up to 3 small grounds on one screw. But the label is the rule, not some random person on the internet.

There is a second option, but really if you 100% just can't get the neutral bar screw undone:

• Turn off the breaker
• Remove the low-voltage wires (probably screw terminals, but can't see) from the transformer
• Loosen the screw on the breaker and remove the hot wire
• Cut the neutral wire as close as possible to the transformer
• Strip the transformer end of the wire to an appropriate length for use with a wire nut
• Wrap white electrical tape over the entire black portion of the wire (i.e., everything except the part you stripped).
• Remove the transformer from the panel

Then when you install the new transformer:

• Black to breaker
• White to old neutral wire with an appropriately sized wire nut
• Green to ground bar or neutral bar. You can't always put grounds on the neutral bar, but since there are already many grounds on the neutral bar, it is presumably a true main panel where that is allowed.

However, I would be concerned about the condition of the neutral bar for both current use (if the corrosion affects the connections) and future use (if one screw won't come out, you will probably have problems with other screws on the bar).

Answer 2

To remove the old transformer:

With the power off, carefully remove the black wire from the breaker, (circled in your pic).

Remove the other black wire from the neutral bar.

Remove the old transformer. REMEMBER THE BOX STILL HAS POWER, work carefully.

To install the new transformer:

Mount the new unit to the side of the breaker box as per instructions.

Attach the neutral (white) wire to the neutral bar

Attach the ground (green) wire to the neutral bar. ( grounds and neutrals can share the same bar in the main breaker box. The old transformer did not have a ground wire because it relied on the mounting to the box to be the ground.)

Attach the black wire to the breaker, ( same breaker as the old unit)

Turn the breaker back on. Done!

Answer 3

They just shorten the circuit up a lot.

Seeing it is inside the panel, it will be safer to turn off the main breaker. Usually the big one on top of all the smaller ones. It should have marking saying it is a 100 or more amps.

Withe the main breaker off just unscrew the old wires.

The new black wire goes to the breaker. The white wire and the ground wire goes with the the white/ground wires. The white wire usually has it's own screw. The ground wires can usually be double up under a screw.

Turn on the main breaker and you should be good.