Equipment Protection

Fuses and breakers are also used to protect electrical appliances and equipment from damage or complete burn out due to overload. The fuse or breaker at the breaker box is sized to protect the wire, but is not necessarily sensitive enough to protect a small-use device plugged in on the circuit. In this instance, a fuse or breaker is generally built into the appliance or electrical equipment to protect it from overload.

Electric Motor PictureFor example, electric motors draw large in-rush currents when they are starting. A typical motor will draw five times as much current while starting compared to its normal running current. Therefore, a motor that draws 3 amps at full-rated load while running, will draw 15 amps while it is starting. A 12 gauge copper wire used to supply the motor with electricity would normally be protected by a 20 amp fuse or circuit breaker. If the motor locks up and draws 15 amps, this current flow will burn out the motor winding very quickly but not cause a 20 amp fuse or breaker to shut off power to the motor. A second fuse or breaker to protect the motor from overloading is clearly necessary in a situations like this.

Note also that when individual equipment fuses or breakers are used, they are used in addition to the regular circuit protection. The fuse or breaker at the main service panel or sub-panel protects the circuit wire against dangerous overloads. The equipment fuse or breaker protects the individual piece of electrical equipment and adds safety to the system.