8 questions · 17% of the Calculations exam
Why A is correct
Ohm’s law gives resistance as voltage divided by current. Dividing 120 volts by 8 amperes gives 15 ohms; multiplying the values would calculate volt-amperes instead.
Why C is correct
Multiply the starting ampacity by the supplied factor: 55 amperes times 0.70 equals 38.5 amperes. Terminal limitations would be checked afterward if the problem supplied them.
Why D is correct
Multiply the continuous load by 1.25: 28 amperes times 1.25 equals 35 amperes. The nameplate current alone omits the continuous-load allowance, and dividing by 1.25 goes in the wrong direction.
Why A is correct
Ohm's law gives current as voltage divided by resistance: 240 ÷ 20 = 12 amperes. Keep units consistent and use only the factors stated; no optional method or unstated demand factor is assumed.
Why C is correct
Apply both supplied factors to the starting ampacity: 75 × 0.80 × 0.91 = 54.6 amperes. Terminal and equipment limitations must then be checked separately.
Why D is correct
Substitute the supplied values: 2 × 12.9 × 30 × 150 ÷ 6 = 19,350 circular mils. A permitted conductor must then be selected at or above the result.
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