Every electrical circuit in a home has a “safe capacity.” Safe capacity is the total amount of power the circuit wires can carry without tripping circuit breakers or blowing fuses. According to the National Electrical Code, the power used by light fixtures, lamps, tools, and appliances, called the “demand,” must not exceed the safe capacity of the circuit.

Finding the safe capacity and the demand of a circuit is easy. Make these simple calculations to reduce the chances of tripped circuit breakers or blown fuses, or to help plan the location of new appliances or plug-in lamps.

First, determine the amperage and voltage rating of the circuit. If you have an up-to-date circuit map these ratings should be indicated on the map. If not, open the service panel door and read the amperage rating printed on the circuit breaker or on the rim of the fuse. The type of circuit breaker or on the rim of the fuse. The type of circuit breaker or fuse indicates the voltage of the circuit.

Use the amperage and voltage ratings to find the safe capacity of the circuit. Safe capacities of the most common household Circuits are given in the table.

Safe capacities can be calculated by multiplying the amperage rating by voltage. The answer is the total capacity, expressed in watts, a unit of electrical measurement. To find the safe capacity, reduce the total capacity by 20%.

Next, compare the safe capacity of the circuit to the total power demand. To find the demand, add the wattage ratings for all light fixtures, lamps, and appliances on the circuit. For lights, use the wattage rating printed on the light bulbs. Wattage ratings for appliances often are printed on the manufacturer’s label. Approximate wattage ratings for many common household items are given in the table on the opposite page. If you are unsure about the wattage rating for a tool or appliance, us the highest number shown in the table to make calculations.

Compare the power demand to the safe capacity. The power demand should not exceed the safe capacity of the circuit. If it does, you must move lamps or appliances to another circuit. Or make sure that the power demand of the lamps and appliances turned on at the same time does not exceed the safe capacity of the circuit.

How to Find Wattage & Amperage Ratings 

Light bulb wattage ratings are printed on the top of the bulb. If a light fixture has more than one bulb, remember to add the wattages of all the bulbs to find the total wattage of the fixture.

Appliance wattage ratings are often listed on the manufacturer’s label. Or use the table of typical wattage ratings on the opposite page

Amperage rating can be used to find the wattage of an appliance. Multiply the amperage by the voltage of the circuit. For example, a 13-amp, 120-volt circular saw is rated for 1560 watt

Circuit # _ 6_   Amps_ 20_  Volts__ 120_  Total capacity_ 2400_(watts)  Safe capacity_1920_(watts)
Appliance or fixture	Notes	Wattage rating
Refrigerator	Constant Use	480
Ceiling Light	3-60 watt bulbs	180
Microwave oven		625
Electric can opener	Occasional use	144
Stereo	Portable boom box	300
Ceiling Light (Hallway)	2 60 Watt Bulbs	120
Total demand:		1849(watts)

Photocopy this sample circuit evaluation to keep a record of the power demand of each circuit. The words and numbers printed in blue will not reproduce on photocopies. In this sample kitchen circuit, the demand on the circuit is very close to the safe capacity. Adding another appliance, such as an electric frying pan, could overload the circuit and cause a fuse to blow or a circuit breaker to trip.

Appliance	Amps	Watts	Appliance	Amps	Watts
Air conditioner (central)	13 to 36 (240-v)	3120 to 8640	Garbage disposer	3.5 to 7.5	420 to 900
Air conditioner (window)	6 to 13	720 to 1560	Hair dryer	5 to 10	600 to 1200
Blender	2 to 4	240 to 480	Heater (portable)	7 to 12	840 to 1440
Broiler	12.5	1500	Microwave oven	4 to 10	480 to 1200
Can opener	1.2	144	Range (oven/stove)	5.5 to 10.8 (240-v)	1320 to 2600
Circular saw	10 to 12	1200 to 1440	Refrigerator	2 to 4	240 to 600
Coffee maker	4 to 8	480 to 960	Router	8	960
Clothes dryer	16.5 to 34 (240-v)	3960 to 8160	Sander (portable)	2 to 5	240 to 600
Clothes iron	9	1080	Saw (table)	7 to 10	840 to 1200
Computer	4 to 7	480 to 840	Sewing machine	1	120
Dishwasher	8.5 to 12.5	1020 to 1500	Stereo	2.5 to 4	300 to 480
Drill (portable)	2 to 4	240 to 480	Television (color)	2.5	300
DVD player	2.5 to 4	300 to 480	Toaster	9	1080
Fan (ceiling)	3.5	420	Trash compactor	4 to 8	480 to 960
Fan (portable)	2	240	Vacuum cleaner	6 to 11	720 to 1320
Freezer	2 to 4	240 to 600	Waffle iron	7.5	900
Frying pan	9	1080	Washing machine	12.5	1500
Furnace, forced-air gas	6.5 to 13	780 to 1560	Water heater	15.8 to 21 (240-v)	3800 to 5040

Typical Wattage Ratings (120-volt Circuit except where noted)

Click below for more options:

Troubleshooting

Panel Upgrades

New Outlets & Circuits

Glossary

Installation Price

Free In-home Lighting Consultation