Breaker Too Big for Wire Size

Electrical wiring comes in many different sizes. Each size is designed to carry up to a certain amount of electrical current. So, different size wires need to be connected to different size circuit breakers (sometimes fuses). If a wire is connected to a circuit breaker that will trip at a current higher than the wire is rated for it is called ‘over-fusing’. This can lead to the wire over heating which can cause the insulation to melt, and possibly a fire. It’s very important to ensure that every wire in a home is protected by a properly sized circuit breaker.

The image below shows a 20 amp breaker with a 15 amp (14 gage) wire on it. It should have a 12 gage wire on it, which is capable of carrying 20 amps. Above this breaker is a 20 amp breaker with the correct size wire on it. You can see the the outside diameter of the two wires is different. Another way to tell that the wire is a 14 gage wire is that it bends easily compared to a 12 gage wire.

One Exception

The one exception to this rule of matching a breaker size to the wire size is on air conditioners. When an air conditioner starts up it can, for a very short time, draw more current than the wire serving it can handle under a steady-state condition. This is fine if it only happens for a short time (a few seconds). In order to allow for this start-up surge in electricity a breaker rated slightly higher than the wiring is rated for can be installed. The maximum size of the circuit breaker is usually documented on the name plate of the condenser/compressor unit outside the home.

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