How to Find an Electrical Short
An electrical short happens when an accidental path is created between the hot line and the neutral wire or the ground in a circuit, generating a connection where there shouldn’t be one. It's usually very obvious when it happens as a short will reveal itself by fuses being repeatedly blown or the circuit breaker tripping repeatedly. It also usually causes a loud popping sound when the circuit is activated.
When a short occurs, it should be addressed right away since this problem could deteriorate the wire and its insulation, or the breaker itself, or even cause a fire. You can find and repair the cause of an electrical short yourself by following the steps below.
Step 1 – Check Appliances
The first thing to do is to take note of every plug, lights, and appliance that is np longer working due to the short circuit. The most likely culprit is the electrical appliance you were using when the short occurred. Unplug it and measure across both flat prongs with an ohmmeter to see if it is shorted. If it's not, look around, on the same circuit for an appliance drawing a lot of power such as a heater or a toaster that was just recently used drawing an excess of current on the breaker. None of it has to be shorted, but if a circuit wired on a 15 Amps circuit that is already drawing 3-4 amps from lights and small appliances is being overloaded by a newly plugged heater requiring 12-13 Amps to operate, the breaker's capacity being overdrawn by a couple of amps will trip itself off. To make sure that it's not caused by a short along the line, switch off and unplug everything on that circuit then switch the breaker back on. With nothing left in the circuit, if the breaker keeps tripping, the problem lies inside the walls.
If the circuit breaker still trips out or if the fuse blows, it could be caused by a faulty breaker, receptacle, switch, or light socket, or a short in the wiring.
Step 2 – Isolating the Breaker
Before starting to work at an electrical circuit, MAKE SURE THERE IS NO POWER IN THAT CIRCUIT BY TURNING OFF THE BREAKER. Confirm it's turned off with the multimeter switching it to AC Volts. Insert the metal probes into the problem receptacle and check for zero volts. If voltage is present, you'll have to find the right breaker and repeat the procedure. once the power is off, remove the wall plate and pull out the wall plug, switch, or light socket to expose the wires.
Step 3 – Check in all Terminal Boxes
With the power (breaker) still turned off, switch the multimeter to ohms. Check the wires for a short by placing one lead of the meter to the black wire and the other to the white wire. If the meter shows infinite ohms or O.L., then the receptacle and its circuit right up to the breaker is good. The breaker, however, could have deteriorated and heat-up/trip from a lower current flow. In this case, an electrician will be required to access the main panel and replace it.
If the meter shows continuity, there is a short circuit that could be anything from a faulty breaker to a defective wire or a faulty receptacle or switch. Remove the black wire from the terminal to isolate the receptacle or other devices from the line and perform the same continuity test between the black and the white wire. If you don't get continuity, replace the faulty receptacle or switch, but if you still get continuity (short) the problem is further along the line. Inspect the cable and all its wires to ensure that there isn't any sign of wear or cuts showing bare copper that could touch somewhere and short out. If all is good, then screw the black wire back to its original terminal, reinstall in the box with the wall plate.
Next, you can proceed to the next electrical box along the circuit and repeat the exact same procedure, thus eliminating each wall plug, switch and light socket from the defective list. If at the end none of the electrical box's device is the cause, but you still measure the short circuit, it's probably caused by a defective breaker. HOWEVER, DO NOT ATTEMPT TO REMOVE THE COVER FROM THE MAIN PANEL SINCE IT IS AN EXTREME DANGEROUS PLACE WITH 200 AMPS OR MORE INSIDE IT! THIS IS WHERE YOU CALL YOUR LOCAL ELECTRICIAN TO FINISH THE TASK!