Question 31
In a three-phase motor circuit, what does 'service factor' on the nameplate indicate?
Question 32
A 480-volt, three-phase motor is drawing significantly higher current on one phase than the others. The motor feels hotter than normal. What is the most likely problem?
Question 33
A three-phase motor hums but does not start, and the overload relay trips shortly after. What is the most likely cause?
Question 34
During troubleshooting, you find that a three-phase motor is drawing significantly higher current on one phase, but the supply voltage is balanced. What is the most likely cause?
Question 35
You are troubleshooting a three-phase motor that hums but does not start. You measure no voltage on one phase at the motor terminals. What is the most likely condition?
Question 36
A three-phase motor fails to start and only hums when energized. Line voltage is correct. Which is the BEST first diagnostic check?
Question 37
Which motor type is most commonly used for general-purpose three-phase industrial loads?
Question 38
A three-phase, 480 V motor draws 30 A at full load. Approximately what is its apparent power in kVA?
Question 39
A 3-phase motor hums but does not start, and one of the three fuses feeding it is found to be open. What condition is this and what risk does it create?
Question 40
A small shop fan has a nameplate that reads 120 V, 1-phase, 60 Hz. What does the '1-phase' marking indicate?
Question 41
After connecting a three-phase motor, the electrician finds that the motor shaft rotates in the opposite direction from the arrow on the housing. What is the usual method to correct this?
Question 42
Which motor type is MOST commonly used for small fractional horsepower loads such as exhaust fans in commercial buildings?
Question 43
A motor nameplate shows 3-phase, 480 V, 15 A full-load current. Approximately what is the motor's apparent power in kVA at full load?
Question 44
Which type of motor is NOT commonly used in industrial applications because of its low starting torque and inability to vary its speed easily?
Question 45
Which type of motor is most likely to be used for a hoist or crane application, due to its ability to develop high starting torque?
Question 46
Which type of motor is often used where the load requires extremely smooth and precise positioning, such as in CNC machines or robotics?
Question 47
In which type of motor will the rotor's speed always be less than the synchronous speed?
Question 48
What is the primary function of the **squirrel cage** in a three-phase induction motor?
Question 49
A three-phase, 480 V motor has a full-load current of 22 A and a power factor of 0.85. Approximately how much three-phase power does it draw at full load?
Question 50
Which of the following is an advantage of a 3-phase motor over a single-phase motor of the same horsepower?
Question 51
What is the function of the 'start' capacitor in a single-phase motor?
Question 52
What is the primary function of a commutator in a DC motor?
Question 53
What does the 'Code Letter' on a motor nameplate indicate?
Question 54
What is the function of the centrifugal switch in a capacitor-start motor?
Question 55
A motor nameplate lists a 'Service Factor' (SF) of 1.15. What does this mean?
Question 56
Which type of motor enclosure is totally sealed to prevent outside air from circulating through the windings, making it suitable for dirty or wet environments?