6 questions · 13% of the Calculations exam
Why D is correct
Use the supplied circuit resistance with Ohm's law: 48 amperes times 0.30 ohm equals 14.4 volts. Relative to 240 volts, that is a 6-percent drop before considering any downstream branch circuit.
Why A is correct
Three-phase apparent power equals 1.732 times line voltage times line current. Dividing 49,883 by 1.732 and then by 480 gives approximately 60 amperes.
Why B is correct
The continuous load contributes 40 times 1.25, or 50 amperes. Adding the 70-ampere noncontinuous load produces a feeder calculation of 120 amperes.
Why D is correct
Three-phase apparent power is 1.732 × 480 × 75 = 62,352 volt-amperes. Keep units consistent and use only the factors stated; no optional method or unstated demand factor is assumed.
Why A is correct
Rearrange Ohm's law: resistance equals voltage drop divided by current. 7.56 ÷ 42 = 0.18 ohm. Keep units consistent and use only the factors stated; no optional method or unstated demand factor is assumed.
Why B is correct
The calculated remainder is 133 − 88 = 45 amperes. Dividing by 1.25 converts the calculated allowance to 36 amperes of continuous load.
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