Licensed Electrical Contractor Branch Circuit Calculations 4

Question 1

A 240V branch circuit is protected by a 50-ampere breaker and supplies an electric range. What is the maximum continuous load in amperes?

Accepted Answer

40 amperes

Answer

Continuous loads are limited to 80% of the overcurrent device rating: 50A × 0.80 = 40 amperes.

Question 2

Per NEC 210.19(A), what must the ampacity of branch circuit conductors be for a continuous load plus noncontinuous load?

Accepted Answer

125% of continuous load plus 100% of noncontinuous load

Answer

NEC 210.19(A)(1) requires conductor ampacity of not less than 125% of continuous load plus 100% of noncontinuous load.

Question 3

A branch circuit serving a 1.5 HP, 120V single-phase motor must have conductors rated at a minimum of what percentage of the motor's full-load current?

Accepted Answer

125%

Answer

NEC 430.22 requires branch circuit conductors for a single motor to be rated at not less than 125% of the motor's full-load current.

Question 4

What is the calculated load for a 12,000 VA central electric heating unit on a branch circuit, after applying the 100% demand factor required by NEC 220.51?

Accepted Answer

12,000 VA

Answer

NEC 220.51 requires fixed electric space heating loads to be calculated at 100% of their total connected load, so 12,000 VA.

Question 5

A branch circuit conductor run of 150 feet uses 12 AWG copper wire at 20A on a 120V circuit. If the resistance of 12 AWG is 1.98 ohms per 1,000 feet, what is the approximate voltage drop?

Accepted Answer

11.88 volts

Answer

VD = 2 × (1.98/1000) × 150 × 20 = 2 × 0.297 × 20 = 11.88V (round-trip conductor length doubled).

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Licensed Electrical Contractor Practice Test

Licensed Electrical Contractor Branch Circuit Calculations 4