My Electric Furnace Is Tripping the Breaker

Significance

• The wiring inside most electric furnaces is protected by one or two internal circuit breakers. In the event of a malfunction within the furnace, the internal breakers usually trip before the breaker in the electrical panel does. For this reason, a tripped breaker in the panel rarely signifies a wiring problem inside the furnace, but rather a problem with the house wiring. The furnace may have been wired with the wrong size wire, or the breaker controlling the circuit may be too small. If the wiring is correct, there may be a short circuit caused by worn insulation or a loose connection.

Breaker Size

• An electric furnace consumes more electricity than virtually any other appliance, typically drawing 60 amps or more when in operation. The breaker controlling it must be rated for that much current, or it trips whenever the furnace comes on. If your furnace is rated for 60 amps, but the breaker is rated for 50, replace the 50-amp breaker with a 60-amp one. Some furnaces draw even more than 60 amps and require larger circuit breakers. The breaker rating is denoted by the number imprinted on its toggle arm, and the current rating of the furnace is stamped on its specifications label, which usually is affixed to the furnace body near the electric terminals.

Wire Size

• The circuit dedicated to powering an electric furnace must be wired with 8-gauge wire, which has a larger diameter than the 10-gauge wire used for 240-volt circuits powering smaller appliances such as electric dryers. If the furnace circuit is wired with 10-gauge wire, the wire overheats when the furnace is on. The overheating can melt the wire insulation or the plastic casing of the furnace receptacle, and hot wires may touch one another, causing a short circuit and tripping the breaker. You must rewire the furnace circuit with wire of the correct size to fix this problem.

Short Circuits

• Short circuits happen when the wires in a circuit cable touch one another, prematurely closing the circuit, generating a high current and tripping the breaker. Shorts can happen when the wire insulation deteriorates, which is more likely to happen in old wiring. They also can happen when wires work themselves loose from the outlet terminals. Eight-gauge wire is very difficult to manipulate, and often comes loose from outlet terminals while you are pushing the wires into the electrical box in preparation for screwing the outlet to the box. To prevent this, crimp ring lugs to the ends of the wires and screw the lugs to the terminals.