AWG = American wire gauge
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How many watts can a 15 amp circuit support?
tkrussell
May 3, 2005, 01:55 AM
Code only allows any circuit to be loaded 80 % of its rated load. As you noted most devices wil not be on all the time, however, there only needs to be one time for all to be on to exceed the allowed ampacity of th circuit, and to be sure there is absolutely no fire hazard, the 80% rule should be followed.
A 15 amp circuit can carry only a total of 1440 watts,which is 80% of the 1800 watts found by mulitplying the volts times amps,15 x 120 x 80%= 1440.
A 20 amp circuit can be loaded 1920 watts, 120 x 20 x 80%=1920 watts.
If the panel was recently replaced I am sure there is a 15 amp breaker because the installer found a #14 wire, which can only use a 15 breaker,and a 20 amp breaker cannot be connected to it.
The furnace blower nameplate of 12 amps does not include startup, or "Locked Rotor Amps". Motors need to be protected by a breaker 125% of the load, 12 x 125%= 15. This can use # 14 wire and a 15 amp breaker, and should be alone on the circuit.
Also having the lights in the basement on a different circuit will come in handy should the furncae breaker ever trip or needs to be shut off, so you can have light to work on the furnace.
As Labman mentioned about refrigerators and freezers, having them on their own circuit is recommended, so if something on the circuit trips the breaker, you will not lose all the food it the refrigeration, but code does not require this, since these units do not draw much current, usually 3-4 amps .
You msut be absolutely sure what size wire you have before installing a larger breaker on it.Either read the markings on the wire insulation, and if you cant see the markings, get one of the wire strippers that have wire gauges on it to measure the wire.