Why Breakers Trip: Overloads, Ground Faults and Short Circuits

Why does a breaker keep tripping?

According to Jack Arnold of Arnold Electric Services, a company working on existing electrical systems in older homes on the northwest side of Chicago, breaker tripping comes down to three main causes: an overloaded circuit, a ground fault, and a short circuit.

Overloaded circuit

His kitchen example: a standard modern kitchen requires seven 20 amp circuits, but older Chicago homes often have two, three or four 15 amp circuits feeding the counter outlets, dishwasher, range hood and disposal. If a toaster and a microwave can't run at the same time, there are probably not enough circuits.

To test it, the electrician has the homeowner run the microwave and toaster, takes the panel cover off and clamps an amp probe on the breaker's wire to measure amperage. A typical kitchen appliance averages about 8 amps, and older Chicago homes were typically wired with 15 amp circuits. The fix is to add additional circuits.

Ground fault

In older homes, a ground fault is usually a metal screw on an outlet that has wiggled loose over time and touches the metal outlet box. An energized part of an outlet, switch or breaker touching a metal box is a ground fault. The breaker can't be reset: it trips the instant it is turned back on.

Short circuit

A short circuit is a cross wire: the hot and neutral touching. One example is a white wire coming out of a wire nut and getting jammed under the wire nut of a hot conductor. As with a ground fault, the breaker trips automatically when reset.