Load Calculation

Load Calculation

Circuits with non-specific loads would be a circuit with receptacles (plugs).  There could be ten receptacles hooked up to a 20-amp circuit with no specific load.  The opposite of that would be a 20-amp circuit which powers a garbage disposal and dishwasher.  The garbage disposal uses about 3 amps and the dishwasher about 7.  In this case, the load is 10 amps which means the circuit is loaded to 50% capacity.  Code advises load of a circuit up to 80%.

To monitor your circuits with non-specific load, if you can determine what receptacles are controlled by a particular circuit, you are on the right path.  Then calculate the load.  Every appliance is supposed to have a data plate attached noting the voltage or current draw (amps or watts).  An example of an 80% load for a 20 amp circuit would be 1,920 watts or 16 amps and for a 15 amp circuit, an 80% load would be 1,440 watts or 12 amps.  If a hair dryer is being used in a bathroom (usually about 1500 watts) and a space heater is used which also uses 1,500 watts, the circuit is now overloaded and the breaker will trip. 

A basic calculation to determine amps is:

Watts = Amps  X  Volts



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