Ramsay Test Technical Aptitude & Knowledge 6

Question 1

A three-phase induction motor is running at 1,740 RPM on a 60 Hz supply with 4 poles. What is the approximate slip of this motor?

Accepted Answer

3.3%

Answer

Synchronous speed for a 4-pole, 60 Hz motor = (120 × 60) / 4 = 1,800 RPM. Slip = (1,800 − 1,740) / 1,800 = 60 / 1,800 = 0.0333, or approximately 3.3%. Slip represents the difference between synchronous and actual rotor speed, which is necessary for torque production in induction motors.

Question 2

In a hydraulic circuit, a pressure-compensated pump maintains 2,000 PSI. The cylinder has a 3-inch bore and a 1.5-inch rod. What is the ratio of the extend force to the retract force when full system pressure is applied to each side respectively?

Accepted Answer

4:3

Answer

Extend force uses the full bore area: π × (1.5)² = 7.069 in². Retract force uses the annular (rod side) area: π × (1.5)² − π × (0.75)² = 7.069 − 1.767 = 5.302 in². Force ratio = 7.069 / 5.302 ≈ 1.333, which simplifies to 4:3. The rod reduces the effective area on the retract stroke, producing less force at the same pressure.

Question 3

A V-belt drive system uses a 4-inch drive sheave on a 1,750 RPM motor and an 8-inch driven sheave. If belt slip is 3%, what is the actual output speed of the driven shaft?

Accepted Answer

848.75 RPM

Answer

Ideal output speed = (drive diameter / driven diameter) × input RPM = (4/8) × 1,750 = 875 RPM. With 3% belt slip, actual speed = 875 × (1 − 0.03) = 875 × 0.97 = 848.75 RPM. Belt slip reduces the velocity ratio, so the driven sheave turns slightly slower than the theoretical calculation predicts.

Question 4

When reading a micrometer, the thimble shows a reading of 0.276 inches on the sleeve, but the technician notices the thimble line falls between two vernier scale lines. The lower vernier line is 3 and the upper is 4, with the thimble appearing two-thirds of the way between them. What is the correct reading to the nearest ten-thousandth?

Accepted Answer

0.2763 inches

Answer

The sleeve reads 0.276 inches. On a vernier micrometer, each vernier graduation represents 0.0001 inch. If the thimble line aligns closest to vernier line 3 (not line 4), the reading adds 0.0003 inch: 0.276 + 0.0003 = 0.2763 inches. The position 'two-thirds of the way between 3 and 4' indicates the 3 line is the closest coinciding line, yielding 3 ten-thousandths.

Question 5

A maintenance technician discovers a 480V, 3-phase motor drawing unequal currents: Phase A = 42A, Phase B = 38A, Phase C = 44A. The nameplate FLA is 40A. Which condition BEST explains this symptom pattern?

Accepted Answer

Voltage unbalance on the supply feeding the motor

Answer

Unequal currents across all three phases — with some above and some below nameplate FLA — is a classic signature of supply voltage unbalance. Voltage unbalance causes disproportionate current unbalance (typically 6–10× the voltage unbalance percentage). A shorted winding would cause one phase to draw dramatically more current. An overload would raise all phases proportionally. A single loose connection causes one phase to drop, not the mixed-high/low pattern seen here.

Ramsay Test Practice Test

Ramsay Test Practice Test

Ramsay Test Technical Aptitude & Knowledge 6