Load Calculation and Services 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 Load Calculation and Services flashcards as text
Under NEC 230.42, the service entrance conductors must have an ampacity not less than the load calculated per Part III of Article 220, but never less than:
Answer: The calculated load only
NEC 230.42(A) requires ampacity not less than the calculated load; the 100A minimum is a service rating rule under 230.79, not a conductor rule.
A commercial load includes 150 kVA of show window lighting. Per NEC 220.14(G), what unit load is used for show window lighting?
Answer: 200 VA per linear foot
NEC 220.14(G) requires show window lighting to be calculated at a minimum of 200 VA per linear foot of show window.
What is the calculated load for two 6 kW household ranges using NEC Table 220.55, Column C?
Answer: 11 kW
NEC Table 220.55 Column C lists the demand for two ranges rated up to 12 kW each as 11 kW.
For a 480/277V, 3-phase, 4-wire commercial service, what is the VA calculation for a balanced lighting load of 300A per phase?
Answer: 207,846 VA
VA = √3 × 480V × 300A ≈ 249,415 VA; for per-phase balanced load on a 277V branch: 277V × 300A × 3 = 249,300 VA — closest answer is 249,415 VA.
Per NEC 220.60, when calculating feeder or service loads, which of the following is a noncoincident load?
Answer: Electric heating and air conditioning loads
NEC 220.60 permits using only the larger of noncoincident loads—such as heating and cooling—since both are unlikely to operate simultaneously.
What is the minimum clearance required from the top of a service mast to the final point of attachment on a building per NEC 230.24(A)?
Answer: 10 feet
NEC 230.24(A) requires service drop conductors to maintain a minimum 10-foot clearance above finished grade at the service entrance.
When sizing a neutral conductor for a 3-phase, 4-wire wye service supplying only fluorescent lighting, NEC 220.61(C)(1) prohibits the neutral reduction because:
Answer: Fluorescent lighting produces harmonic currents that increase neutral loading
NEC 220.61(C)(1) disallows neutral reduction for nonlinear loads like fluorescent lighting because triplen harmonics can cause the neutral to carry more than phase current.