IEC Electrical Calculations and Theory 2

Question 1

A 240V single-phase circuit supplies a 4,800W resistive load. What is the current draw?

Accepted Answer

20A

Answer

I = P / V = 4,800 / 240 = 20A.

Question 2

What is the total resistance of a 10Ω and 15Ω resistor connected in parallel?

Accepted Answer

6Ω

Answer

1/R = 1/10 + 1/15 = 5/30, so R = 6Ω.

Question 3

A 3-phase, 480V motor draws 30A at 0.85 power factor. What is the true (real) power consumed?

Accepted Answer

21,168W

Answer

P = √3 × V × I × PF = 1.732 × 480 × 30 × 0.85 ≈ 21,168W.

Question 4

What happens to total capacitance when two capacitors are wired in series?

Accepted Answer

It is less than the smallest individual value

Answer

Series capacitors combine via the reciprocal formula, always yielding a total less than the smallest capacitor.

Question 5

In AC circuits, the term 'impedance' refers to:

Accepted Answer

The total opposition to current including resistance and reactance

Answer

Impedance (Z) is the vector sum of resistance (R) and reactance (X) in an AC circuit.

IEC - Independent Electrical Contractors Practice Test