Ramsay Test Electrical Knowledge 6

Question 1

A 480V, 3-phase motor draws 18A under full load. If the power factor is 0.82 lagging, what is the motor's approximate true power consumption?

Accepted Answer

12.2 kW

Answer

True power (kW) = √3 × V × I × PF = 1.732 × 480 × 18 × 0.82 ≈ 12,224W ≈ 12.2 kW. The power factor of 0.82 represents the ratio of true (real) power to apparent power, so multiplying the apparent power by 0.82 gives the actual working power consumed.

Question 2

When performing insulation resistance testing with a megohmmeter on a motor winding, a technician gets a reading of 0.5 MΩ after one minute. According to standard practice, this motor should be:

Accepted Answer

Taken out of service — the reading indicates dangerously degraded insulation

Answer

The industry rule of thumb (IEEE 43) requires a minimum of 1 MΩ plus 1 MΩ per kV of operating voltage for the motor to be considered safe to energize. A reading of 0.5 MΩ falls below even the baseline 1 MΩ threshold, indicating moisture intrusion, contamination, or insulation breakdown — the motor must be taken out of service.

Question 3

In a series RLC circuit operating below its resonant frequency, the circuit's net reactive behavior is:

Accepted Answer

Capacitive, because XC > XL

Answer

At frequencies below resonance, the capacitive reactance (XC = 1/2πfC) is greater than the inductive reactance (XL = 2πfL). Because XC dominates, the net impedance is capacitive, current leads voltage, and the circuit behaves like a capacitor. At resonance XL = XC; above resonance the circuit becomes inductive.

Question 4

A technician measures 120V between L1 and ground, 120V between L2 and ground, but only 120V between L1 and L2 on a system that should be 240V single-phase. The most likely cause is:

Accepted Answer

Both hot conductors are in phase — there is no phase shift between them

Answer

In a normal 240V single-phase center-tap system, L1 and L2 are 180° out of phase, so the voltage between them is 120 + 120 = 240V. Reading only 120V between L1 and L2 means the two hots are in phase (0° apart), not 180° apart — a classic sign of incorrect transformer wiring or a single-phase supply fed from two conductors of the same phase. An open neutral would cause imbalanced loads, not this phase symptom.

Question 5

According to the NEC, the maximum allowable voltage drop for a combination of feeder and branch circuit conductors serving a sensitive load is:

Accepted Answer

5% total — with no prescribed split between feeder and branch

Answer

NEC 210.19(A) Informational Note No. 4 and 215.2(A)(1) Informational Note No. 2 recommend (not mandate) that the combined voltage drop for feeders and branch circuits not exceed 5% total for sensitive electronic loads. The NEC itself does not prescribe a mandatory split between feeder and branch — the 3%/2% split is a common design recommendation from FPN, but the hard guidance is a 5% combined maximum.

Ramsay Test Practice Test

Ramsay Test Practice Test

Ramsay Test Electrical Knowledge 6