Journeyman Electrician’s Exam Journeyman Electrician's Motors and Motor Controls 4

Question 1

In a two-speed motor (consequent pole), changing from low speed to high speed requires:

Accepted Answer

Reconnecting the stator windings to change the number of effective poles

Answer

Consequent pole motors change speed by reconnecting stator windings to alter the effective number of magnetic poles, which changes synchronous speed.

Question 2

What is the primary function of the overload relay in a magnetic motor starter?

Accepted Answer

To protect the motor against sustained overcurrent that causes overheating

Answer

Overload relays protect the motor from sustained overcurrent (overloads) that would cause excessive heat buildup and winding damage over time.

Question 3

According to NEC 430.32(A), a continuous-duty motor with a service factor of 1.15 must have overload protection set to trip at no more than what percentage of nameplate FLA?

Accepted Answer

125%

Answer

NEC 430.32(A)(1) requires overload protection to trip at not more than 125% of FLA for motors with a service factor of 1.15 or higher.

Question 4

A 'wye-delta' reduced-voltage starter transitions the motor from wye to delta configuration. What is the purpose of this transition?

Accepted Answer

To reduce starting current to approximately 1/3 of across-the-line current during start

Answer

During wye starting, each winding receives line voltage ÷ √3, reducing starting current to about 1/3 of across-the-line (delta) starting current.

Question 5

Under NEC Article 430, the term 'controller' refers to:

Accepted Answer

Any switch or device used to start and stop a motor

Answer

NEC 430.81 defines a controller as any switch or device that is normally used to start and stop a motor by making and breaking the motor circuit current.

Journeyman Electrician’s Exam Practice Test

Journeyman Electrician’s Exam Practice Test

Journeyman Electrician’s Exam Journeyman Electrician's Motors and Motor Controls 4