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Lights in garage and garage door stopped working. Breaker didn't blow. Other items on the breaker are working. Opened up ceiling light socket and in the junction box saw this: enter image description here

So on this circuit are two ceiling garage lights, a plug in the ceiling for garage door opener, a porch light, and inside the house, wall plugs in an "office". The garage ceiling lights are on three-way switch set-up. The breaker did not blow. The plugs in the office work. Home was built in 1982 (and in US).

In this junction box the neutrals and grounds are tied together. (Is that supposed to be like that?) There is a black wire tied off to nothing. There is 90 volts between the white/black/black group and the white/ground group.

The failure seemed to occur after some siding work on the house (using two-inch nails) but I cannot be 100% sure - though it was that evening we noticed it. One switch of the three-way ceiling light circuit, the porch light, and porch light switch are in the wall where siding work is taking place. They have the porch light on the outside removed at the moment for the siding work. The office wall sockets have 118v. The switches do use the push-in holes and not the screws to connect the wires.

Is it possible it is a nail hit the wire and would cause these symptoms without blowing the breaker? Why does the office have 118v? The office is between the breaker box and garage. Is it possible bad neutral connections (which I understand can cause voltage drops?

  • What voltage do you measure at the porch light? – ThreePhaseEel Oct 16 '16 at 23:58
  • The porch light wires (the light is still removed but taped up) shows 47 volts between line and neutral or ground (with the switch for the light on the inside of the garage turned on, of course). – gd2141 Oct 17 '16 at 0:47
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    Neutral and ground should not be connected anywhere except at the main box. You need to figure out what is actually going on here and fix it. – keshlam Oct 17 '16 at 0:51
  • Remove all lightbulbs from fixtures on the suspect circuit that still have bulbs in them and unplug all appliances from the circuit, then turn the breaker for the circuit off, verify that the circuit's dead, and tag+remove the hot and neutral wires from the breaker and neutral busbar respectively. Then measure the resistance between the hot and neutral and report this number back to us. – ThreePhaseEel Oct 17 '16 at 1:01
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    It's relatively unlikely that a nail could either break a wire or short two together, and the fact that the breakers didn't trip rules out the latter. It's more likely that in removing the porch light, they disconnected a pass-thru wiring and thus cut power to (or from) the other lights. – Carl Witthoft Oct 17 '16 at 14:05
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Should neutral and ground wires tied together in junction box?

No. Neutral and ground should never be tied together in a junction box.

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    +1 yes, this puts neutral current on the equipment ground that is normally considered to "safe". A VERY dangerous situation. The ONLY place neutrals and grounds should be connected together is the main service. – ArchonOSX Oct 23 '17 at 16:41

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