Licensed Electrical Contractor Electrical System Design & Installation 4

Question 1

For a 480V, 3-phase commercial lighting circuit, which raceway fill percentage applies when more than two current-carrying conductors are present per NEC 310.15?

Accepted Answer

A derating factor must be applied to conductor ampacity

Answer

NEC 310.15(C) requires ampacity adjustment (derating) when more than three current-carrying conductors are bundled or in a conduit due to heat buildup.

Question 2

A transformer secondary with a 3-wire 240V single-phase system must have which conductor identified for proper system grounding?

Accepted Answer

The grounded (neutral) conductor at the center tap

Answer

On a 240V single-phase 3-wire system, the center-tap grounded conductor (neutral) must be identified, typically with white or gray insulation.

Question 3

Which method is acceptable for splicing conductors within an electrical junction box?

Accepted Answer

Wire connectors (wire nuts) rated for the conductors

Answer

NEC 110.14 requires splices to be made with listed devices such as wire connectors (wire nuts) that provide both mechanical and electrical connection.

Question 4

When calculating the load for a commercial kitchen, the NEC allows which demand factor to be applied to electric cooking equipment?

Accepted Answer

Demand factors from NEC Table 220.56 based on number of units

Answer

NEC Table 220.56 provides demand factors for commercial cooking equipment, allowing load reduction based on the number of cooking units installed.

Question 5

What is the purpose of an isolation transformer in an electrical system design?

Accepted Answer

To electrically isolate circuits and eliminate ground loops

Answer

An isolation transformer separates primary and secondary circuits magnetically, eliminating direct electrical connection and reducing ground loops and noise.

Licensed Electrical Contractor Practice Test

Licensed Electrical Contractor Practice Test

Licensed Electrical Contractor Electrical System Design & Installation 4