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You are considering the purchase of a heat pump system with aresistive heating element in the air-handler for back-up during the extra cold winter months when the temperature is below the heat pump's capability. The manufacturer's technical data states the maximum current draw for the unit you are looking at is 18 amps at 240 volts, 1-phase. The circult breaker that you would have to install to carry this resistive load is:

A. 20 amp, 2-pole
B. 40 amp, 1-pole
C. 30 amp, 1-pole
D. 45 amp 2-pole
E. 25 amp. 2-pole

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abdullahjawaid1

Answer:

The correct answer is E. 25 amp, 2-pole

Explanation:

In United States, the mains voltage is 120 Volts at 60 Hz, Single Phase (One Hot Leg).

Firstly, as the resistive heater requires 240 Volts therefore 2 hot wires/ 2 phase will be used with single neutral wire. Hence, 2 pole breakers will be required.

Secondly, the ampere rating of breakers is selected with 25 % overload capacity as per NEC standards. Therefore, 18 x 1.25 = 22.5 A.

According the calculations and as per available options, 25 A, 2 pole  breaker is selected.

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