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My doorbell transformer (picture attached) is determined to be dead because the output voltage is zero, while power socket voltage from the junction box is about 122. Thus, the doorbell transformer needs to be replaced or the wiring to the doorbell transformer needs to be taken care of.

Doorbell transformer attached to a junction box with power sockets

Inside of junction box (after shutting down the power, of course) is shown below:

Inside of junction box

As we can see, the wires to the doorbell transformer are connected to the power socket panel. The connection is so firm that I can't pull the wires out. Is there any trick to disconnect the wires from the power panel so that I can replace the doorbell transformer? Or should I just replace the junction box and the doorbell transformer as a whole device?

Thanks in advance.

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    The word you're looking for is "receptacle". That's that thing with the sockets. It is also called a "yoke", though to be more precise the yoke is the metal bracket with the ears, the one you took the screws out of to get here. – Harper - Reinstate Monica Oct 27 '19 at 1:06
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Do not replace the junction box. It is a standard junction box and there is nothing wrong with it.

Backstab connections fail more often than transformers

Look at the receptacle. See how the wires are connected? They're "back wired" with a backstab style connection. That is only allowed for 14 AWG solid wire, the receptacle's labeling plainly says

PUSH IN #14 CU SOLID WIRE FOR 15A BRANCH CIRCUIT ONLY.

CU = copper. It is then repeated in French.

Looking at the transformer's ground wire it definitely stranded wire that has been tinned with solder to keep it from getting a case of the frizzies. The ground wire has been horked onto the already-occupied ground screw in an impressive display of bad workmanship.

Equally bad workmanship is obvious in the attaching of the transformer wires to backstabs. The wires are stranded and certainly not 14 AWG. This is a violation of NEC 110.3 which requires the instructions and labeling of the receptacle be followed (14 AWG solid only).

Since backstabs have a spectacular failure rate (open circuit) even when they are used to spec, we should expect this to be a failed backstab.

So, I would remove the transformer wires from the backstab (if it's possible to do this while also facepalming), and move each wire to the appropriate screw terminal. I would also pause to inspect the wire for any arcing or galling, because that would explain the mystery.

As far as actually removing the wires, there should be a little slot into which you can jab a tiny screwdriver, and sort of pry away from the wire and that should reduce the extraction force somewhat. Otherwise feel free to just use an excessive amount of force. Worst case the wire will break off inside the backstab and you'll have to strip off another 1/4" to attach it to the screw.

When removing #14 wires, just twist the receptacle back and forth about 60 degrees repeatedly while using serious force. Don't cut; wire length is precious in most cases.

While you're at it, fix the ground

The ground installation was acceptable until this transformer came along. Now it is one too many wires on that ground screw. Move the "U" loop on the receptacle screw so you have about 2" of extra length sticking out (instead of the 1/2" now sticking out). Wire-nut the transformer ground wire to that.

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    I find myself wondering-- if back stabs fails so often, why a) are they still manufactured? and b) why hasn't code disallowed their use? I never noticed the #14ga requirement on the receptacle before. Thanks for pointing that out. – peinal Oct 27 '19 at 17:02
  • @peinal I often have the same question about non-TR receptacles as well – Jacob Krall Oct 27 '19 at 17:58
  • As a side note, is it common for junction boxes to be metallic? Down here I only seen them in older Soviet apartments, and always wondered how safe was it, considering all the ends that might come loose inside the box (although they shouldn't, of course). – Gnudiff Oct 27 '19 at 21:23
  • @Gnudiff they are fine if grounding is competent. Also they play very well with metal conduit, where the conduit carries the ground. – Harper - Reinstate Monica Oct 28 '19 at 0:08
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If you look very closely you will see a small rectangular slot adjacent to each wire "stab in" hole. A thin tool, such as a small slotted screwdriver (or even a thick paper clip) can be inserted there to release the wires.

Those "stab in" wire connections are notoriously lame; I would recommend that when you wire up the new transformer you use a single wire connected to the screw terminal of each side as a pigtail, and connect all additional wires using a wire nut.

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  • I actually forgot about those "rectangular slots" . I never have a small screwdriver handy when I come across backstabs... + – JACK Oct 27 '19 at 10:55
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First turn off the power. The trick is to hold on to a wire and twist the outlet back and forth while pulling the wire. You will see the wire start to remove from the outlet. You will want to remove all the wires except for the ground. Use the screw terminals when reconnecting the outlet. Bend a hook around the black hot wire and screw it in to the outlet on the side with the brass screws. Hook the white wire around the side with the silver screws. You might want to try the transformer again by hooking it's wires to the screw terminals because the back stab connections can sometimes go bad. If the transformer is bad, replace it with a similar one. If it comes with stranded wire, get a few spade connectors and crimp them to the wire and then connect the transformer to the screw terminals on the outlet.

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If the transformer doesn’t have an internal fuse you need to add one because the fault current of the transformer is less than the breaker protecting the wiring. Having been an fireman I have seen numerous houses burn down because of small transformer.

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    Where are you on this planet? Listed Class 2 power sources are inherently current-limited... – ThreePhaseEel Oct 27 '19 at 22:22

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