CPE Electrical Systems & Controls 2

Question 1

A plant engineer needs to select a motor for a 100 HP centrifugal pump. Which NEMA enclosure type is most appropriate for an outdoor, wash-down environment?

Accepted Answer

NEMA 4X (Watertight, Corrosion-Resistant)

Answer

NEMA 4X provides watertight and corrosion-resistant protection, making it the correct choice for outdoor wash-down environments.

Question 2

According to NEC Article 430, the minimum short-circuit and ground-fault protection for a 460V, 50 HP induction motor with a full-load current of 65A using an inverse-time breaker is:

Accepted Answer

175A

Answer

NEC 430.52 allows inverse-time breakers at up to 250% of FLC for motor branch-circuit protection; the standard selection closest to 250% × 65A = 162.5A is 175A.

Question 3

In a VFD-driven motor system, which component is primarily used to reduce reflected wave voltage at motor terminals caused by long cable runs?

Accepted Answer

dV/dt filter or output reactor on the output side

Answer

Output reactors or dV/dt filters placed between the VFD and motor attenuate reflected wave voltages caused by impedance mismatch on long cable runs.

Question 4

A 480V delta-wye transformer feeds a panel. A single-line-to-ground fault occurs on the secondary. What is the fault current's primary path back to the source?

Accepted Answer

Through the equipment grounding conductor back to the transformer secondary neutral

Answer

Fault current returns to the source via the equipment grounding conductor back to the transformer secondary neutral, which is the local source of power.

Question 5

What is the primary purpose of a shunt trip coil in a molded-case circuit breaker?

Accepted Answer

To allow remote electrical opening of the breaker upon receipt of a control signal

Answer

A shunt trip coil allows the breaker to be remotely opened via a DC or AC control signal, used in emergency shutdown or fire alarm applications.

(CPE) Certified Plant Engineer Practice Test

(CPE) Certified Plant Engineer Practice Test

CPE Electrical Systems & Controls 2