Calculating Circuit Load
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An overloaded circuit can heat up to extreme temperatures creating a serious fire hazard and a threat to life and property. To protect against overload always know the capacity of the circuit and how much power is drawn by appliances before adding a new outlet. To calculate circuit capacity multiplying the amp rating of the breaker by the voltage of the circuit or:
(Circuit Breaker Amps X Circuit Volts = Wattage Capacity)
For a 120 volt circuit with a 15 amp breaker this would be 1800 watts. The total load on the circuit should not exceed 80% of this total or 1440 watts.
To determine the watts drawn on a circuit calculate the load of all the devices plugged into that circuit. First determine which electrical appliances are plugged into a circuit by turning off the circuit breaker and counting all the devices that stop working. Next, add the watts drawn by each device. For example, a circuit with a ceiling fan, TV and two floor lamps with 60 watt bulbs adds up to 670 watts if all these devices are running at the highest speed, all at the same time. This is 46% of the available capacity for a 15 amp/120 volt circuit, making this circuit a good candidate for adding a new electrical outlet.
The wattage rating information for a particular device may be on a label or imprinted on the back. If no wattage rating is displayed the load can be calculated by multiplying the amps drawn by the appliance by the voltage of the circuit. If neither the amps nor the wattage ratings for a device is known the chart below lists common household appliances and the average wattage ratings for each to aid in calculating the load of a circuit.
Wattage Rating for Common Household Appliances
| Appliance | Average Load in Watts |
| Blender | 400 |
| Can Opener | 150 |
| Ceiling Fan | 10—100 |
| Ceiling Fan w/Light Kit (2–40watt bulbs) | 90—180 |
| Ceiling Light Fixture (2–60watt bulbs) | 120 |
| Clock Radio | 40—150 |
| Clothes Dryer | 4,000—5,500 |
| Clothes Iron | 600—1,200 |
| Clothes Washer | 500—1,000 |
| Coffee Maker | 600—1,500 |
| Dehumidifier | 500 |
| Desktop Computer | 570 |
| Dishwasher | 1,000—1,500 |
| Electric Range | 4,000—8,000 |
| Food Freezer | 300—600 |
| Garbage Disposal | 500—900 |
| Hair Dryer | 400—1,500 |
| Hand Mixer | 150—250 |
| Laser Printer | 1,000 |
| Microwave Oven | 1,000—1,500 |
| Refrigerator | 400—600 |
| Stereo | 50—150 |
| Television | 50—450 |
| Three Way Lamp (30–70–100watt bulb) | 30—100 |
| Toaster Oven | 500—1,450 |
| Water Heater | 2,000—5,500 |
| Window Air Conditioner | 800—2,500 |
