Ramsay Test Electrical 4

Question 1

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

Accepted Answer

12,237 W

Answer

True power (W) = √3 × V_line × I_line × PF = 1.732 × 480 × 18 × 0.82 ≈ 12,237 W. The √3 factor is required for 3-phase calculations, and the power factor of 0.82 reduces apparent power to real (true) power.

Question 2

A technician measures 240V across a series circuit containing a 40Ω resistor and an unknown resistor. The current in the circuit is 3A. The voltage drop across the 40Ω resistor is 120V. What is the value of the unknown resistor?

Accepted Answer

40 Ω

Answer

Voltage across the unknown resistor = 240V − 120V = 120V. Using Ohm's Law: R = V/I = 120V / 3A = 40Ω. Both resistors drop equal voltage, confirming they are equal in value.

Question 3

Which of the following conditions would cause a capacitor in a motor start circuit to fail by becoming shorted rather than open?

Accepted Answer

Voltage surge or transient spike exceeding the capacitor's voltage rating

Answer

A voltage surge or transient spike that exceeds the capacitor's rated voltage can rupture the dielectric insulation between the plates, creating a direct conductive path — a shorted capacitor. Extended run time and heat typically cause electrolyte degradation leading to an open, not a short.

Question 4

When using a clamp-on ammeter to measure current in a single-phase 120V circuit, a technician wraps both the hot and neutral conductors through the clamp jaw and reads 0A, even though a load is clearly operating. What is the most accurate explanation?

Accepted Answer

The equal and opposite magnetic fields of the two conductors cancel each other, producing a net zero reading

Answer

When both conductors of the same circuit pass through the clamp jaw, the current flowing toward the load (hot) and returning from the load (neutral) are equal in magnitude but opposite in direction, producing equal and opposite magnetic fields that cancel. The meter sums them to zero. Only one conductor should pass through the jaw.

Question 5

A 120V, 60Hz circuit has a coil with 0.5H of inductance and negligible resistance. What is the inductive reactance (X_L) of the coil?

Accepted Answer

188.5 Ω

Answer

X_L = 2π × f × L = 2 × 3.1416 × 60 × 0.5 = 188.5Ω. The formula requires multiplying 2π by both the frequency and the inductance in henries. Common errors include forgetting the factor of 2 or using the wrong inductance value.

Ramsay Test Practice Test

Ramsay Test Practice Test

Ramsay Test Electrical 4