A 20-amp circuit is not limited by outlets, but by amps or watts used at once through the same circuit, and the circuit should not exceed 80 percent of its maximum load, according to the National Electric Code. With this guideline, a 20-amp circuit should not exceed 16 amps.

The circuit breaker or fuse will automatically shut off the circuit if the limit is exceeded, preventing overheating wires, surges and fires. A person can determine the amount of wattage a 20-amp circuit can handle by multiplying the circuit's volts by its amperage. With this formula, a 20-amp, 120-volt circuit can handle 2,400 watts.