Electrical System Design & Installation Flashcards
7 cards from real Licensed Electrical Contractor practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Electrical System Design & Installation flashcards as text
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?
Answer: A derating factor must be applied to conductor ampacity
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.
A transformer secondary with a 3-wire 240V single-phase system must have which conductor identified for proper system grounding?
Answer: The grounded (neutral) conductor at the center tap
On a 240V single-phase 3-wire system, the center-tap grounded conductor (neutral) must be identified, typically with white or gray insulation.
Which method is acceptable for splicing conductors within an electrical junction box?
Answer: Wire connectors (wire nuts) rated for the conductors
NEC 110.14 requires splices to be made with listed devices such as wire connectors (wire nuts) that provide both mechanical and electrical connection.
When calculating the load for a commercial kitchen, the NEC allows which demand factor to be applied to electric cooking equipment?
Answer: Demand factors from NEC Table 220.56 based on number of units
NEC Table 220.56 provides demand factors for commercial cooking equipment, allowing load reduction based on the number of cooking units installed.
What is the purpose of an isolation transformer in an electrical system design?
Answer: To electrically isolate circuits and eliminate ground loops
An isolation transformer separates primary and secondary circuits magnetically, eliminating direct electrical connection and reducing ground loops and noise.
For a 3-phase motor installation, the overload protection device must be set to trip at no more than what percentage of the motor's nameplate full-load current for a service factor of 1.15?
Answer: 125%
Per NEC 430.32(A)(1), overload protection for motors with a service factor of 1.15 or more must trip at no more than 125% of nameplate FLA.
In a 277/480V wye distribution system, which load is most appropriately connected line-to-neutral?
Answer: 277V fluorescent or LED lighting
277V is the phase-to-neutral voltage in a 480V wye system, making it ideal for fluorescent and LED lighting fixtures rated 277V.