Journeyman Electrician’s Exam Journeyman Electrician's Motors and Motor Controls 3

Question 1

A reduced-voltage soft starter is primarily used to:

Accepted Answer

Reduce mechanical stress and inrush current during motor starting

Answer

Soft starters gradually ramp up voltage to limit starting current and reduce mechanical shock on the driven load during startup.

Question 2

According to NEC 430.83, a motor controller must have a voltage rating not less than:

Accepted Answer

The maximum circuit voltage

Answer

NEC 430.83 requires controllers to have a voltage rating not less than the maximum circuit voltage where they are applied.

Question 3

What does the term 'locked-rotor current' (LRC) describe?

Accepted Answer

Current drawn at the instant of starting when the rotor is stationary

Answer

Locked-rotor current is the high inrush current drawn when voltage is applied and the rotor has not yet begun to rotate.

Question 4

Which type of motor protection device responds to both overtemperature and overcurrent conditions by monitoring the motor winding temperature directly?

Accepted Answer

Thermistor (PTC) embedded in winding

Answer

A PTC thermistor embedded in the motor winding changes resistance dramatically at a set temperature, triggering protection based on actual winding temperature.

Question 5

A variable frequency drive (VFD) controls motor speed by varying:

Accepted Answer

Both the output frequency and voltage applied to the motor

Answer

VFDs vary both frequency and voltage (maintaining a constant V/Hz ratio) to control motor speed while preventing magnetic saturation.

Journeyman Electrician’s Exam Practice Test

Journeyman Electrician’s Exam Practice Test

Journeyman Electrician’s Exam Journeyman Electrician's Motors and Motor Controls 3