How to find a short in electrical home wiring

Written by jerry walch Google
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Short circuits can happen almost anywhere in an electrical wiring system but are most likely to occur where the continuity of the wiring systems has been intentionally broken. Rodents have been known to chew through NMC (nonmetallic sheathed cable) and cause shorts. Termites have been known to find their way inside metal conduit systems and cause shorts. However, as a rule, most short circuits occur in junction boxes, ceiling outlet boxes, device boxes, fixed appliances, service panels and other similar locations when wires come loose from terminals or work free of a spliced connection. Occasionally a short will occur when someone drives a nail through a cable or cuts into a cable when doing repairs.

Skill level:

Things you need

  • Electrician's screwdrivers
  • Digital multimeter
  • Diagonal pliers/wire cutters
  • Lineman's pliers/electrician's pliers
  • Wire strippers
  • Needle-nose pliers
  • AWG (American wire gauge) 12, insulated solid copper wire, black
  • AWG 12, insulated copper wire, white
  • AWG 12, bare, solid copper wire
  • Yellow wire nuts
  • Electrical tape

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  1. 1

    Go to the electrical box and look for tripped breaker switches. Turn the circuit breaker all the way to the off position, unplug and/or turn off everything connected to that circuit. Reset the breaker. If the circuit breaker resets now, you know that the short is in something connected to the circuit and not in the system wiring itself. When troubleshooting any electrical problem, always work from the easiest to the most difficult.

  2. 2

    If the circuit breaker still can't be reset, check the receptacle outlets and switches on the circuit for looseness. Device boxes are the next most likely place for a short to occur, and if you find one that has a loose device in it, check that one first. Short circuits occur in these boxes when wires come loose and make contact with a metal box or with another wire of a different phase or polarity. Hot wires and neutral wires touching one another or a hot wire making contact with the system grounding conductor or making contact with a grounded metal device box are the principal causes.

  3. 3

    If there's a light on that circuit and the circuit breaker trips when you turn the light on, check for a short at the switch, in the lighting outlet box or in the light fixture itself.

  4. 4

    If the circuit feeds fixed appliances like a dishwasher, trash compactor, garbage disposal or baseboard heat unit and trips out when you turn the appliance on, look for a short in that appliance's wiring.

  5. 5

    If the short circuit was caused by someone driving a nail through a cable, by someone drilling into a cable or by someone cutting into a cable, you can repair it by opening up the wall and installing a junction box at that point, but if you do that, the box must remain accessible. You will have to close the wall up using some type of decorative but easily removed panel. The National Electric Code requires that junction boxes be accessible without having to remove any permanent part of the finished structure.

    The other route that you can take is to route a new run of cable to replace the damaged section. If you're working on the first floor over an unfinished basement or crawlspace, this option is probably your best and easiest route to take.

  6. 6

    For short caused by a rodent chewing through a cable, disconnect all the devices on that circuit. Set your digital multimeter to the ohms range and then check between all the wires in each cable segment until you find a segment that reads "0" ohms between the black wire and either the white wire or the bare wire. That the segment that has the short. You have the same choices here as you had in Step 5.

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