Electrical Theory and Fundamentals
What the exam tests
This domain checks whether you can apply Ohm’s law, AC power relationships, series/parallel rules, and voltage-drop math to field and plan-review problems. Expect single-phase and three-phase calculations, power factor, conductor resistance, and transformer or motor basics.
Core rules
- Ohm’s law: V = I × R; power in a resistive circuit: P = V × I = I²R.
- AC: apparent power S = V × I (VA); real power P = V × I × cosθ (W); reactive power Q = V × I × sinθ (var).
- Series: current is common, voltages add, resistances add. Parallel: voltage is common, currents add, and the reciprocal resistance rule applies.
- Single-phase voltage drop: VD = 2 × K × I × L / CM, where L is one-way length and K is 12.9 for copper, 21.2 for aluminum. Three-phase: VD = 1.732 × K × I × L / CM.
- Root-mean-square values are the default for AC ratings; peak = RMS × 1.414 for a sine wave.
Worked example
A 240 V single-phase branch supplies 50 A at 0.95 power factor over a 100 ft one-way copper run using 8 AWG (16,510 circular mils). Voltage drop: 2 × 12.9 × 50 × 100 / 16,510 = 7.81 V. Percent drop = 7.81 / 240 = 3.25%. Real power = 240 × 50 × 0.95 = 11,400 W. The drop is just over the common 3% branch-circuit recommendation, so a 6 AWG conductor would be the next check.
Traps
Using the round-trip length twice; applying the copper K to aluminum; treating VA as watts at low power factor; and using peak voltage in nominal calculations.