8 questions · 17% of the Calculations exam
Why B is correct
For the balanced service total, divide apparent power by 240 volts. Twenty-eight thousand eight hundred volt-amperes divided by 240 volts equals 120 amperes.
Why C is correct
For the balanced 120/240-volt service total, divide volt-amperes by 240 volts. The result is 38,400 divided by 240, or 160 amperes; dividing by 120 would double-count the balanced total.
Why D is correct
A demand factor reduces the connected value: 18,000 volt-amperes multiplied by 0.65 equals 11,700 volt-amperes. Subtracting 65 as a raw number or dividing by the factor does not apply the stated percentage.
Why A is correct
Apply 125 percent only to the continuous portion: 32 amperes times 1.25 equals 40 amperes. Add the 84-ampere noncontinuous portion to obtain 124 amperes.
Why B is correct
Three-phase apparent power is 1.732 × 208 × 125 = 45,032 volt-amperes, approximately 45 kVA. Keep units consistent and use only the factors stated; no optional method or unstated demand factor is assumed.
Why D is correct
Reverse the demand calculation by dividing the carried load by the factor: 31,500 ÷ 0.75 = 42,000 volt-amperes.
Why A is correct
Subtract the noncontinuous load first: 146 − 96 = 50 amperes of calculated allowance. Dividing that allowance by 1.25 gives 40 amperes of actual continuous load.
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