CSLB C-10 Electrical ContractorPlanning and EstimatingMedium
A commercial building client is planning a new general office area. The electrical plans specify 120V, 20A branch circuits for general-purpose receptacle outlets. The total floor area of the office space is 3000 square feet. According to NEC 220.14(J), what is the minimum general lighting load (in VA) that must be used for calculations for this office area?
- A10500 VA
- B12000 VA
- C9000 VA
- D7500 VA
Show answer & explanationAnswer & explanation
Correct answer: A. 10500 VA
For general office buildings, NEC Table 220.12 specifies a unit load of 3.5 VA per square foot for general lighting. Therefore, for a 3000 sq. ft. office, the minimum general lighting load is 3000 sq. ft. * 3.5 VA/sq. ft. = 10,500 VA.
Why the other options are wrong
- B. 12,000 VA would imply 4.0 VA/sq. ft., which is not the correct unit load for general office buildings.
- C. 9000 VA would be calculated using 3.0 VA/sq. ft., which is incorrect for general office buildings.
- D. 7500 VA would be calculated using 2.5 VA/sq. ft., which is for different occupancy types.
General Lighting Load Calculation (NEC)
A method of determining the minimum required lighting load for a given occupancy type and floor area, using unit load values from NEC Table 220.12.
- NEC Table 220.12 provides unit load values in VA per square foot for various occupancy types.
- The calculated general lighting load is used for service and feeder sizing.
- This is a minimum load; actual lighting loads may be higher depending on design.
Memory trick: Lighting load: 'Area' times 'Unit' equals 'Total' VA for the building.