E2 Motors and Transformers 2

Question 1

According to the NEC, what is the minimum branch-circuit conductor ampacity for a single motor with a full-load current of 40 A?

Accepted Answer

50 A

Answer

40 A

Answer

44 A

Answer

48 A

Question 2

A transformer nameplate lists an impedance of 5.75%. This value is primarily used to calculate:

Accepted Answer

Available fault current

Answer

No-load losses

Answer

Efficiency at full load

Answer

Magnetizing inrush current

Question 3

What NEC article governs the installation of air-conditioning and refrigeration equipment motors?

Accepted Answer

Article 440

Answer

Article 430

Answer

Article 445

Answer

Article 460

Question 4

A 480V delta–wye transformer secondary supplies a 208Y/120V panelboard. The neutral conductor on the secondary is derived from:

Accepted Answer

The wye-connected secondary center point

Answer

The delta primary winding center tap

Answer

A separately derived grounding electrode

Answer

The primary overcurrent device

Question 5

Per NEC 430.52, the maximum rating of an inverse-time circuit breaker used as motor branch-circuit protection for a Design B squirrel-cage motor is:

Accepted Answer

250% of FLC

Answer

150% of FLC

Answer

200% of FLC

Answer

400% of FLC

Question 6

Which motor nameplate data item is used to determine the correct overload protection size per NEC 430.32?

Accepted Answer

Service factor and nameplate current

Answer

Horsepower and locked-rotor current

Answer

NEMA design letter and frame size

Answer

Torque class and efficiency rating

Question 7

A 75 kVA, 480–208Y/120V transformer is considered a separately derived system. What grounding electrode conductor size is required for a 4/0 AWG secondary conductor per NEC Table 250.66?

Accepted Answer

2 AWG copper

Answer

4 AWG copper

Answer

1/0 AWG copper

Answer

3/0 AWG copper