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We have a ceiling fan in our bedroom with a dual knob switch on the wall to control the fan and light separately. Yesterday the light stopped working but the fan was still going so we changed out the switch today for a new one. My father performed the work and did it without turning the electricity off first. All was fine until he went to push the switch back into the wall to close everything up when there was a loud pop and smoke and the circuit tripped. He said that something must have gotten smushed in there when he pushed the box back into the wall and tripped the circuit. The ground wire from the wall (the bare metal one) had a little notch in it and the ground wire from the switch had a black mark on them afterwards. But he closed it up, we turned the circuit back on and everything is working fine with no popping or anything.

So my question is…is this something that I should probably have someone come out and double check to make sure there is not a fire hazard situation going on in there? I’m a little scared about the damage to the ground wires, but my father said that since everything is working and nothing is tripping, it should be good to go.

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    "my father said that since everything is working and nothing is tripping, it should be good to go" -- Not to dishonor your father, but do you want to take technical advice from someone who repairs home wiring with the power on? Aug 28 at 18:50
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    Everything worked as it should(except the one doing the work). The ground wire with the notch should be replaced someday. Ground wire did get smushed against hot screw/wire. Usually happens when everything is put back and you turn the power back on.
    – crip659
    Aug 28 at 18:50
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    Ok I'm not here for the dad slander, LOL. I just need to know if it should be ok now that everything is working and nothing is popping or tripping the circuit.
    – Aloysius
    Aug 28 at 19:06
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    @A.I.Breveleri when I was in college I had a job as an electrician doing both commercial and residential work. The electricians that trained me frequently worked on hot 120v circuits (as did I). Obviously it’s better to turn off the power first, but I wouldn’t necessarily discredit someone merely because they decide not to flip off the breaker to swap a switch.
    – ARich
    Aug 29 at 6:39
  • idk what the rules are where you are, but in the UK you're not allowed to run bare earth, you must sheath it between the cable & socket. That way, it cannot short when you're reassembling. Look carefully at this picture, you'll see the earth is only sheathed where it's exposed, the cable itself is bare earth. i.stack.imgur.com/TBAaQ.jpg
    – Tetsujin
    Aug 29 at 11:34

4 Answers 4

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It happens to the best.

When squishing the wires back there is litle control how they bend.

The pesky naked Ground bend so that it touched one of the Hot wires.

You do need someone to open and take look, and correct the situation.

One spark does not mean it is over, the wires are still dangerously close.

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    Thank you for answering my question and being kind! Would you suggest I turn the circuit off until someone can come look at it or do you think I can leave it on for now?
    – Aloysius
    Aug 28 at 19:11
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    Possibly good choice to turn it off
    – Ruskes
    Aug 28 at 19:12
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    Yep, agreed Ruskes. I was asked by one of my brothers to troubleshoot a circuit that was constantly tripping. When I got there, I asked him to turn on the breaker and sparks few out of an outlet. As Jeff Foxworthy would say: "There's your clue"! Turned out the situation was exactly as you described, a bare (pesky! LOL) ground wire contacted the hot terminals. I removed the outlet, inspected and slightly rerouted the wiring in the outlet box. Some ppl recommend taping over the screws on the sides of outlets with electrical tape to prevent this from happening. I don't, just a thought. Aug 28 at 19:17
  • To prevent home burning up, they make a product called AFCI. Which is a breaker that detects arcs and turns off. You might have small arcs going on, but not large enough to trip regular breaker.
    – Ruskes
    Aug 28 at 19:17
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    Ran out of space. Yes, WITH THE POWER OFF, the outlet should be removed to inspect the wires. If damaged, it needs to be repaired, obviously. Aug 28 at 19:18
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Would turn the power off to that switch and recheck for any other damage.

The ground wire with the notch should be replaced. Should not use damaged wires. They can break or have higher resistance(heat) if used.

The switch(they are cheap) can also be replaced if it makes you feel safer, but probably just an option.

This can sometimes happen when working on switches/outlets. Sometimes the ground wire comes into contact with the hot/live screw when putting it back into the box. Some people will place electrical tape around the screws to prevent this or make sure to be careful when putting back in the box.

Probably the only damage was the notch and the black mark and the breaker did it's job by tripping. The black mark can probably be just wiped off.

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    Aside from the electrical tape around all 4 sides to cover up the exposed metal screws, I was also taught to make sure my wire ends were stripped to exactly the correct length, so bare copper was in contact with the screw terminal, but no bare wire was visible further up, outside the device where something might touch it.
    – Armand
    Aug 28 at 21:33
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    Probably why most devices have those handy-dandy strip gauges.
    – crip659
    Aug 28 at 21:50
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Before I begin, and just to make a point, while it was foolish to the Nth degree to change that switch with the breaker on, doing so has demonstrated a weakness in the wiring that you might not have learned about otherwise until a serious problem occurred. Do NOT take that to mean that it's ever a good idea to leave the breaker on. I'm merely pointing out that that a bad choice has had the unusual but not unheard of consequence of leading you to wisdom.

Don't depend on that.

The reality is that, bless his heart, your father made a mistake. It's human, we all get it. But it's better to not make the mistake. That's the wisdom you're learning here.

OK, the three most common reasons why this happens:

  1. You have a metal outlet/switch box, which should be grounded, and while pushing the wires back something hot (usually the screw posts) touched the box. You're explaining damage to the ground wire and your box is likely modern plastic so this is probably not the problem.

  2. You have a bare ground wire (very common) that bent over and touched a hot screw post (or a wire too long or otherwise badly connected to that post) on the switch (should be a mark on the post where ignition occurred). Note that if the switch is "on" then both posts are hot. If the switch was "off" only one post was hot.

  3. You have a wire nut connecting two or more hot wires together and one or more of the wires was stripped too far, leaving a small portion of exposed wire outside the wire nut cap — and that bit of bare hot wire touched something like your bare ground wire or the metal mounting bracket of the switch (should be a mark on the hot wire near the base of the cap).

As I mentioned, I believe #1 can be ignored. It's caused by someone's shaking hands or a weird angle of entry before seating the screws that allowed the screw posts to touch the metal wall. Once installed, those posts and walls are intentionally separated and quite safe. However, that is only relevant if you have a metal switch box. Most switch boxes today are plastic to avoid this very problem (and a lot of others that are similar). However, once those screws are tight, the problem no longer exists — but you said you saw a mark on your ground wire, so it's not #1.

The other two demand that you remove the switch and check what happened because the problem still exists. That electrical short can happen again as wire tension relaxes or as your house shifts, which can gently move the wires. Or as use of the switch itself causes slight (very slight) vibrations inside the box. All of that might seem far-fetched... but it your house that's going to burn down with you and your family potentially in it. Are they so far-fetched that it's not worth re-seating the wires?

  • Check the wire nuts (white and black) to be absolutely sure no bare wire is peeking out from under the cap. In fact, you'd be surprised how often 3+ wires in a cap can result in one that slipped out a bit or is actually quite loose. This is notably true if you reused the original wire nut rather than using a new one.

  • Check the ground wire bundle to be sure it's pushed flat against the back of the box and check the wire from the bundle to your switch to be sure it has an appropriate "S" bend that will allow it to collapse away from the screw posts. Personally, I like to bend that wire to the top or bottom of the box (whichever is closer to the ground wire mount on the switch) and then S-bend it so that it's collapsing along the bottom or top of the box, not the sides.

While it's always good advice to invite a professional to review the work, this isn't something that's complex. You can do this. just remember to shut the darn breaker off. There is no convenience that's worth your life.

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No clue as to your location - so assume local regs allow bare earth wires. While not the rules, it does make sense to sheathe them, or insulate the m in some way, obviously had that been done, there'd be no sparks.

Worth stripping down properly (power off), and making sure the other wires fit into the receptacles properly. Dad maybe left enough bare wire sticking out to catch the earth, which, while you're at it, should be sheathed so there's no chance of any bare wire touching any other. At the same time, check all wires haven't burned through at all, making them thinner than they should be, causing problems later.

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