Almost every home electric appliance has a rating plate. Printed on the rating plate is a rating in amperes of the amount of electric current the appliance will draw when it is on. If two appliances are running on the same voltage, as they do in homes, ampere ratings are also a way of comparing the amount of power the appliances use.
Fuses and circuit breakers are rated in amperes. If the sum of the ampere ratings for the appliances that are plugged into a circuit is greater than the rating of the fuse or circuit breaker for the circuit, the circuit breaker will trip (or the fuse will blow).
Many appliances draw more current while they are starting up than they require while running. The initial current draw may be greater than the ampere rating on the rating plate. Most electric motors need two to three times their rating plate amps to start. When electric service is restored after a power outage, all the appliances that are turned on start at once, and the load may be enough to trip circuit breakers.
When extension cords are used, the ampere rating of the appliance and the length of the cord determine the required wire gauge of the extension cord. The thicker the wire, the small its gauge: a 12-gauge wire is much heavier than a 16-gauge wire. As a result, the 12-gauge wire can carry more current.
If too small a cord is used, the voltage will be less than the appliance needs and the appliance may be damaged. There is also a fire hazard from an overheated cord.
|Length of cord|
|50 feet||100 feet||150 feet|
† In 1999, UL stopped approving 18-gauge extension cords. The standard new cord is 16-gauge.
*Only for use on a 20-ampere circuit. Most circuits in homes are 15 ampere.
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Last revised: 27 July 2016.