How to Find a Short Circuit

Written by dale yalanovsky
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How to Find a Short Circuit
Use a multimeter to find short circuits. (multimeter image by dinostock from Fotolia.com)

A short circuit in the wiring of a residence, an appliance or a vehicle occurs as the result of old or faulty wiring; compromised insulation; or the failure of a part---a light switch, for example. Identify and correct short circuits using either of two methods.

Skill level:
Moderate

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Things you need

  • Multimeter
  • A partner
  • Adjustable wrench
  • New fuse

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Instructions

    For Your Vehicle

  1. 1

    Open the bonnet of your car and truck and locate the battery.

  2. 2

    Attach an adjustable wrench to the negative battery cable nut and turn it counterclockwise to loosen it. Detach the negative battery cable from the battery.

  3. 3

    Set your multimeter an amperage of 10.

  4. 4

    Place the red or positive multimeter probe on the negative battery cable. Place the black or negative multimeter probe on the negative battery post.

  5. 5

    Read the amperage on the multimeter. If it reads zero, turn the amperage scale setting to 9, and read the amperage on the multimeter again. Reduce the amperage setting by 1 point per reading as you monitor the multimeter. If the multimeter still reads zero when you have reduced the scale setting 1 point per reading all the way to and including zero, no short circuit exists in the system. If at any point the meter indicates an amperage draw, however, a short circuit exists.

  6. 6

    If a short circuit exists, keep the probes on the post and cable as a partner removes one fuse at a time. When, upon removal of a fuse, the amperage drops to zero, note the accessory served by that fuse. That is the source of the short circuit.

    For Your Home

  1. 1

    Unplug all home appliances and turn off all lights, heating and air conditioning and the water heater.

  2. 2

    Turn off the main electrical power source at the breaker box and reset any tripped breaker or replace any blown fuse.

  3. 3

    Flip the main switch of the breaker box back to the on position. If a breaker is tripped or a fuse is blown during this step, the short circuit is in an electrical receptacle or switch, and each one on that particular circuit must be examined.

  4. 4

    Turn on each switch one at a time if the breaker or fuse does not immediately open up when reset or installed. If any switch when turned on causes a breaker to trip or a fuse to blow, you have found the short circuit in the line. If the switches do not trip a breaker or blow a fuse, proceed to the next step.

  5. 5

    Plug a small appliance, like a fan or a hair dryer, into each of the receptacles and turn the appliance on. If the breaker trips or the fuse blows when you turn the appliance on, you have found the short circuit, and the receptacle must be replaced. If no receptacle trips a breaker or blows a fuse, proceed to the next step.

  6. 6

    Plug in all of the appliances that you initially unplugged. If a breaker trips or a fuse blows, you have found the short circuit. The appliance or the cord is the location of the short circuit and must be repaired or replaced.

Tips and warnings

  • If the breaker box fails, you will be unable to reset individual breakers.
  • Contact a qualified electrician if the breaker box fails or the procedure described for finding a short circuit in your home fails.

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