So i am worried about a fire hazard. My hot and neutral wire are packed together into a metal conduit. If there was a screw that accidentally gets screwed into the conduit and connects the hot and neutral wires together, what would happen?

  • Is this a hypothetical question or "asking for a friend"? Seems like an odd question to ask unless it actually happened. OK, so 'fess up, what really happened? It's the only way for us to properly answer the question. The 2 answers (as of this time) are both correct so I won't elaborate beyond them. Just curious WHY you are asking this...enquiring minds want to know! Aug 12, 2020 at 14:54
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    Metal conduit is about as secure an installation as you're going to get. EMT has some degree of resistance to screw penetration. FMC and Rigid, you simply will not put a screw or nail into that. In all cases if a fastener or drill manages to get through, the fastener will be well grounded, so when it bites into the neutral, instant GFCI trip, and when it bites into the hot, instant overcurrent trip. Aug 12, 2020 at 14:56
  • Bad things. Don't do it. Metal pipes are your friend though. And proper upstream circuit protection such as GFCI's and AFCI's.
    – face.
    Aug 12, 2020 at 18:11
  • @GeorgeAnderson Anderson - Just trying to connect an old FMC to new FMC with a screw in coupling. I was afraid that the screw went in too far and connected the wires. However, nothing blown with the breakers when I turned the power on.
    – Jumper89
    Oct 3, 2020 at 22:38

2 Answers 2


Normally if the proper breaker or fuse was used it would trip the breaker or blow the fuse. Normally the conduit would contain all the damage. Less commonly the fast arc in the pipe will vaporize enough copper that it will clear the fault before the breaker trips.

The wire could be very hard to pull out until the screw is removed, or if the wire is blown clear you can use the wire length to determine where the pipe was damaged.

The damaged piece of conduit should be replaced because the screw penetration will leave a sharp point in the conduit that will tear the insulation on new wire.

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    I suppose we should also ask why type of protection was on the circuit. Just over-current, AFCI? GFCI? That would certainly affect our response. Aug 12, 2020 at 14:57
  • If the breaker is faulty, it'll keep pumping "juice" into the pipe (with a scary increasing drone sound) until either the connection breaks or something melts at the panel.
    – face.
    Aug 12, 2020 at 18:09
  • @GeorgeAnderson I guess I could add "If the wires hit are on the load side of a GFCI or AFCI receptacle it is possible it could trip the device before a breaker or fuse could act". Aug 13, 2020 at 15:29

A spark with corresponding sound effects, and if everything works as designed, the fuse will blow or circuit breaker will trip. Depending on whether the conduit is metal or plastic, and which wire the screw hits first, you could also be shocked or electrocuted.

  • Question states "metal conduit."
    – Ecnerwal
    Aug 12, 2020 at 15:10

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