309A Motor Controls

Question 1

What is the maximum overcurrent protection permitted for a motor branch circuit with a full-load current of 40 A using an inverse-time circuit breaker?

Accepted Answer

100 A

Answer

40 A

Answer

50 A

Answer

80 A

Question 2

What is the purpose of a motor overload relay?

Accepted Answer

To protect the motor against sustained overcurrent conditions

Answer

To protect against short circuits

Answer

To protect against ground faults

Answer

To protect against voltage surges

Question 3

In a three-phase motor starter, what is the function of the holding coil (contactor coil)?

Accepted Answer

To keep the contactor contacts closed after the start button is released

Answer

To provide overcurrent protection

Answer

To reduce starting current

Answer

To reverse the motor direction

Question 4

What is the standard overload relay trip setting for a motor with a nameplate FLA of 28 A and a 1.15 service factor?

Accepted Answer

32.2 A

Answer

28 A

Answer

35 A

Answer

42 A

Question 5

What type of motor starter reduces the starting current to approximately one-third of the full-voltage starting current?

Accepted Answer

Wye-delta starter

Answer

Full-voltage starter (across-the-line)

Answer

Autotransformer starter at 80% tap

Answer

Part-winding starter

Question 6

What is the purpose of a jog function on a motor controller?

Accepted Answer

To momentarily energize the motor for precise positioning

Answer

To run the motor at half speed continuously

Answer

To reverse the motor direction

Answer

To provide dynamic braking