Ramsay Test Motors and Controls 1 — Questions and Answers
Question 1: What does the abbreviation 'FLA' mean on an electric motor nameplate?
- Full Load Amperes (Correct answer)
- Frequency Load Adjustment
- Full Line Amps
- Forward Load Amps
Correct answer: Full Load Amperes
FLA stands for Full Load Amperes, indicating the current the motor draws when operating at rated voltage and rated horsepower output.
Question 2: What is the synchronous speed of a 4-pole AC induction motor connected to a 60 Hz power supply?
- 1800 RPM (Correct answer)
- 3600 RPM
- 900 RPM
- 1200 RPM
Correct answer: 1800 RPM
Synchronous speed = (120 × frequency) / number of poles = (120 × 60) / 4 = 1800 RPM.
Question 3: A squirrel cage induction motor gets its name from the design of which component?
- The rotor, which uses aluminum or copper bars short-circuited at both ends (Correct answer)
- The stator, which is wound with insulated copper coils
- The end bells, which are shaped like a cage for ventilation
- The capacitor bank, which resembles a cage structure
Correct answer: The rotor, which uses aluminum or copper bars short-circuited at both ends
The rotor of a squirrel cage motor consists of conductive bars (aluminum or copper) embedded in laminations and short-circuited at each end by end rings, resembling a squirrel cage.
Question 4: What is the primary purpose of the overload relay in a motor starter?
- To protect the motor from damage caused by sustained overcurrent (Correct answer)
- To limit the inrush current during motor startup
- To regulate motor speed under varying load conditions
- To provide short-circuit protection for the motor branch circuit
Correct answer: To protect the motor from damage caused by sustained overcurrent
Overload relays detect excessive current sustained over time and trip the starter to prevent motor winding damage from heat buildup.
Question 5: A three-phase motor that was running normally suddenly begins running at reduced speed under full load. What is the most likely cause?
- One phase of the three-phase supply has been lost (single-phasing) (Correct answer)
- The motor's cooling fan has failed
- The supply voltage is too high
- The motor bearings have seized partially
Correct answer: One phase of the three-phase supply has been lost (single-phasing)
Loss of one phase (single-phasing) causes the motor to run on single-phase power, drastically reducing torque and speed while dramatically increasing current draw.
Question 6: On a dual-voltage motor, the high-voltage connection wires the stator coils in which configuration?
- Series, providing higher impedance and lower current draw (Correct answer)
- Parallel, providing higher voltage with increased current draw
- Delta, providing lower voltage and higher current
- Wye, providing the highest available voltage
Correct answer: Series, providing higher impedance and lower current draw
For high-voltage operation, the dual-voltage motor's winding groups are connected in series, which doubles the impedance and halves the current compared to the low-voltage (parallel) connection.
Question 7: What does a motor's 'service factor' (SF) indicate on the nameplate?
- A multiplier showing how much above rated load the motor can carry intermittently without damage (Correct answer)
- The recommended maintenance interval in operating hours
- The percentage of time the motor can run at full load continuously
- The maximum ambient temperature rating for safe operation
Correct answer: A multiplier showing how much above rated load the motor can carry intermittently without damage
A service factor of 1.15 means the motor can safely handle 115% of its rated horsepower for short periods, provided voltage, frequency, and temperature are within limits.
Ramsay Test Motors and Controls 1
What does the abbreviation 'FLA' mean on an electric motor nameplate?