Licensed Electrical Contractor Motors and Motor Controls 2

Question 1

What is the purpose of a motor's service factor (SF) rating?

Accepted Answer

Indicates allowable overload capacity without damage

Answer

Indicates the motor's insulation class

Answer

Specifies the minimum supply voltage

Answer

Defines the locked-rotor current multiplier

Question 2

A 480V, 3-phase motor draws 28A at full load. Per NEC, the minimum branch circuit conductor ampacity before applying any derating is:

Accepted Answer

35A

Answer

28A

Answer

42A

Answer

49A

Question 3

Which motor protection device responds to both overload current AND phase loss conditions?

Accepted Answer

Electronic (solid-state) overload relay

Answer

Thermal magnetic circuit breaker

Answer

Eutectic-alloy overload relay

Answer

Dual-element time-delay fuse

Question 4

In a wye-delta reduced-voltage starter, motor torque during the wye (starting) step is approximately:

Accepted Answer

33% of full-voltage starting torque

Answer

100% of full-voltage starting torque

Answer

67% of full-voltage starting torque

Answer

50% of full-voltage starting torque

Question 5

What does NEMA frame designation 56 indicate about a motor?

Accepted Answer

The shaft height is 56/16 inches (3.5 inches) from the base

Answer

The motor has a 56 hp rating

Answer

The stator bore diameter is 5.6 inches

Answer

The motor weighs 56 pounds

Question 6

A motor nameplate shows 'Code G.' What does this indicate?

Accepted Answer

Locked-rotor kVA per horsepower range (5.6–6.29)

Answer

Motor efficiency class

Answer

Insulation temperature class

Answer

Motor design letter (torque characteristic)

Question 7

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

Accepted Answer

Article 430

Answer

Article 240

Answer

Article 310

Answer

Article 440