PMMI Industrial Electricity Practice Test

How many 1200-watt hair dryers can be operated by a 120V circuit protected by a 20 amp circuit breaker?

0 1 2 3

Correct Answer:

Explanation:

The main idea is how current, voltage, and power relate on a circuit. A device that uses 1200 watts at 120 volts draws current I = P / V = 1200 / 120 = 10 amperes. A 20-amp circuit breaker can supply up to 20 amperes, so you can run up to two of these dryers at the same time (2 × 10 A = 20 A). Three would require 30 amperes, which would trip the breaker. In practice, startup surges can affect current, but the straightforward calculation shows two is the limit for this setup.

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