IEC Motors and Motor Controls 2

Question 1

A motor nameplate shows a service factor of 1.15. What does this mean?

Accepted Answer

The motor can operate continuously at 115% of its rated load

Answer

A service factor of 1.15 means the motor can operate continuously at 115% of its nameplate horsepower without damaging insulation.

Question 2

Which type of motor starter uses reduced voltage to limit inrush current during starting?

Accepted Answer

Autotransformer starter

Answer

An autotransformer starter reduces starting voltage via a transformer, which significantly reduces inrush current during motor startup.

Question 3

What is the purpose of a motor's overload relay?

Accepted Answer

To protect the motor from sustained overcurrent due to overloading

Answer

Overload relays protect motors from sustained overcurrents caused by mechanical overloads, which generate excess heat and can damage windings.

Question 4

A three-phase motor is wired for wye (Y) connection. Compared to a delta connection, the phase voltage is:

Accepted Answer

Lower than the line voltage by a factor of √3

Answer

In a wye connection, phase voltage equals line voltage divided by √3 (approximately 0.577 × line voltage).

Question 5

Which NEC article primarily governs the installation of motors, motor circuits, and controllers?

Accepted Answer

Article 430

Answer

NEC Article 430 covers motors, motor circuits, and controllers including overcurrent protection and disconnecting means requirements.

IEC - Independent Electrical Contractors Practice Test