Load Calculations Flashcards

According to NEC 220.18, what is the minimum load in VA that must be used for a household electric dryer when the nameplate rating is less than 5,000 W?

Answer: 5,000 VA

NEC 220.54 (formerly 220.18) requires a minimum load of 5,000 VA (5 kW) for each electric clothes dryer, regardless of the nameplate rating.

What demand factor does NEC Table 220.44 allow for the portion of a non-dwelling receptacle load that exceeds 60,000 VA?

Answer: 50%

NEC Table 220.44 allows a 50% demand factor on the receptacle load that exceeds 60,000 VA for non-dwelling occupancies.

When sizing a feeder for six household electric ranges each rated at 12 kW, what is the demand load per NEC Table 220.55?

Answer: 43,000 VA

Table 220.55 Column C lists 43 kW demand for six ranges rated 8¾–12 kW each (maximum demand factor applied).

A 480V, 3-phase, 4-wire system supplies a 150 kVA transformer. What is the full-load primary current?

Answer: 180.4A

I = kVA × 1000 ÷ (√3 × V) = 150,000 ÷ (1.732 × 480) = 150,000 ÷ 831.36 ≈ 180.4A.

Under NEC 220.60, when diverse loads such as heating and cooling cannot operate simultaneously, what is the rule for including both in the feeder calculation?

Answer: Add only the larger load

NEC 220.60 (noncoincident loads) permits omitting the smaller of two loads that will not operate simultaneously from the feeder calculation.

What is the calculated load in VA for general lighting in a 2,400 sq ft dwelling using the NEC unit load of 3 VA per sq ft?

Answer: 7,200 VA

2,400 sq ft × 3 VA/sq ft = 7,200 VA per NEC Table 220.12 for dwelling occupancies.

Per NEC 430.24, when two or more motors share a feeder, conductor ampacity must be based on the sum of all motor FLCs plus what percentage of the largest motor FLC?

Answer: 25%

NEC 430.24 requires feeder conductors sized at 125% of the largest motor FLC plus the FLC of all other motors on the feeder.