Ramsay Test Electrical Knowledge 4

Question 1

A 480V, 3-phase motor draws 18A per phase at full load with a power factor of 0.82 lagging. What is the approximate true power (kW) consumed by the motor?

Accepted Answer

12.2 kW

Answer

True power P = √3 × V × I × PF = 1.732 × 480 × 18 × 0.82 ≈ 12,237W ≈ 12.2 kW. Many candidates confuse apparent power (kVA) with true power (kW) — multiplying by the power factor is essential for 3-phase calculations.

Question 2

A technician measures voltage drop across a 150-foot run of 12 AWG copper wire (resistance ≈ 1.98 Ω per 1,000 ft) carrying 15A. What is the approximate one-way voltage drop?

Accepted Answer

2.97V

Answer

Resistance of 150 ft = (150/1000) × 1.98 = 0.297 Ω. Voltage drop = I × R = 15 × 0.297 ≈ 2.97V. The round-trip (total conductor length) would be 300 ft, but the question asks for one-way drop. Confusing one-way vs. round-trip is a common error.

Question 3

Which wiring method is MOST appropriate when installing conductors in a Class I, Division 1 hazardous location where flammable vapors may be present under normal operating conditions?

Accepted Answer

Rigid metal conduit (RMC) with threaded fittings

Answer

NEC Article 501 requires threaded rigid metal conduit or threaded steel intermediate metal conduit in Class I, Division 1 locations. EMT set-screw fittings are not explosionproof, FMC is only permitted for short equipment connections under strict conditions, and standard MC cable is not suitable for Division 1 areas.

Question 4

Two capacitors — 40 µF and 60 µF — are connected in series across a 120V supply. What is the voltage across the 40 µF capacitor?

Accepted Answer

72V

Answer

In series, capacitors share the same charge (Q). Total capacitance = (40×60)/(40+60) = 24 µF. Q = C_total × V = 24 µF × 120V = 2,880 µC. V across 40 µF = Q / C = 2,880 / 40 = 72V. The smaller capacitor holds MORE voltage — the opposite of series resistors.

Question 5

A transformer nameplate reads: 10 kVA, 2400V primary, 240V secondary. The secondary winding has 80 turns. How many turns does the primary winding have?

Accepted Answer

800

Answer

The turns ratio equals the voltage ratio: N_primary / N_secondary = V_primary / V_secondary → N_primary / 80 = 2400 / 240 = 10 → N_primary = 800 turns. The kVA rating is relevant only for current calculations, not turns.

Ramsay Test Practice Test

Ramsay Test Practice Test

Ramsay Test Electrical Knowledge 4