CME System Design and Installation 2

Question 1

When designing a service entrance for a commercial building, what is the minimum clearance required above a flat roof (not readily accessible) for service-drop conductors per NEC 230.24?

Accepted Answer

3 feet

Answer

NEC 230.24(A) Exception No. 2 permits 3 feet above a roof not readily accessible where the voltage does not exceed 300V between conductors.

Question 2

A 480/277V three-phase four-wire system is being designed for a large office building. Which grounding electrode conductor size is required for a 500 kcmil copper service conductor per NEC Table 250.66?

Accepted Answer

1/0 AWG

Answer

NEC Table 250.66 requires a 1/0 AWG copper grounding electrode conductor for service conductors of 350–600 kcmil.

Question 3

In a fire pump installation, what is the minimum voltage drop permitted at the motor terminals under locked-rotor conditions?

Accepted Answer

Voltage must not drop below 65% of motor nameplate voltage

Answer

NFPA 20 and NEC 695.7 require that the voltage at fire pump motor terminals shall not drop below 65% of nameplate voltage under locked-rotor conditions.

Question 4

When installing a paralleled conductor set for a feeder, what is the minimum conductor size permitted for each parallel conductor per NEC 310.10(H)?

Accepted Answer

2/0 AWG

Answer

NEC 310.10(H)(1) requires each parallel conductor to be at least 1/0 AWG for copper or 1/0 AWG for aluminum, but practical parallel sets begin at 1/0; the minimum is 1/0 AWG.

Question 5

A master electrician is designing a switchboard installation. Per NEC 408.18, what is the minimum headroom required in front of a switchboard?

Accepted Answer

6.5 feet

Answer

NEC 408.18(A) requires a minimum headroom of 6.5 feet in front of switchboards.

(CME) Certified Master Electrician Practice Test

(CME) Certified Master Electrician Practice Test

CME System Design and Installation 2