Electrical Contractor Electrical System Design & Installation Flashcards
6 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 6 Electrical Contractor Electrical System Design & Installation flashcards as text
When designing a commercial electrical system, what is the NEC-required minimum height for service entrance conductors over a public roadway?
Answer: 18 feet
NEC Section 230.24(B) requires service-drop conductors to maintain a minimum clearance of 18 feet over public streets and roadways.
In a 208/120V three-phase, four-wire wye system, what is the voltage measured between any two phase conductors?
Answer: 208V
In a wye-connected system with 120V phase-to-neutral, the line-to-line voltage is 120 × 1.732 = approximately 208V.
What is the maximum allowable voltage drop recommended by the NEC for a combination of feeder and branch circuit conductors?
Answer: 5%
NEC recommends a maximum total voltage drop of 5% for the combined feeder and branch circuit, with no more than 3% on either individually.
When installing a 400-amp service in a commercial building, what is the minimum size copper conductor required for the grounding electrode conductor?
Answer: 1/0 AWG
Per NEC Table 250.66, a 400-amp service using copper conductors up to 500 kcmil requires a minimum 1/0 AWG copper grounding electrode conductor.
What type of electrical system grounding is required by the NEC for a 480/277V, three-phase, four-wire system supplying a commercial building?
Answer: Solidly grounded
The NEC requires 480/277V wye systems supplying line-to-neutral loads to be solidly grounded per Section 250.20(B).
Per NEC Article 220, what is the general lighting load demand factor applied to the first 10,000 VA of general lighting in a commercial occupancy?
Answer: 100%
NEC Table 220.42 requires the first 10,000 VA of general lighting load to be calculated at 100% demand factor.