General Electrical Knowledge and Electrical Theory
What to master
Ohm's law (E = I × R) and its power forms (P = I × E = I²R = E²/R) drive nearly every calculation on this exam, so know which quantity is given and which is being asked for. Series circuits share current; parallel circuits share voltage; combination circuits reduce branch by branch. In AC you must add reactance: X_L = 2πfL, X_C = 1/(2πfC), and impedance Z = √(R² + X²), with power factor = R/Z. Single-phase power is P = E × I × PF; balanced three-phase power is P = √3 × E_line × I_line × PF. Transformers trade voltage for current by turns ratio, and a 120/240 V single-phase service is a 240 V system whose grounded neutral makes 120 V available line-to-neutral.
Traps
Mixing line and phase values on three-phase problems; forgetting to double the conductor length in voltage-drop math; treating watts as volt-amperes on inductive loads; ignoring resistance change with temperature; and confusing nominal voltage with actual operating voltage.
Worked example
A 20 A, 240 V single-phase load sits 120 ft from the panel, and 8 AWG copper has R = 0.778 Ω per 1000 ft. Voltage drop = 2 × I × R × length in kft = 2 × 20 × 0.778 × 0.120 = 3.73 V, about 1.6%. Rule of thumb: keep feeders near 2% and branch circuits near 3% so total drop stays within 5%.