The lighting load for dwellings and other NEC listed occupancies is generally determined by which of the following?

The lighting load for dwellings and other NEC listed occupancies is generally determined by which of the following?

• A. Volt-amps per sqft
• B. Amps per sqft
• C. Watts per sqft
• D. Kilovolt-amps per sqft

Answer: (A)

Lighting load is calculated using volt-amps per square foot because the NEC standardizes how lighting demands are expressed in terms of apparent power, not just real power. Using VA per square foot lets you sum lighting with other loads on feeders and services while accounting for potential differences in power factor from different lighting types and ballasts. To apply it, multiply the area in square feet by the prescribed VA per square foot (for dwellings and listed occupancies this is the common approach). If you later need current, divide the total VA by the supply voltage. Amps per square foot isn’t used because it ties the calculation to voltage and power factor, and watts per square foot ignores reactive power, while kilovolt-amps per square foot is just another way of saying VA per square foot but is not the standard term used here.

Lighting load is calculated using volt-amps per square foot because the NEC standardizes how lighting demands are expressed in terms of apparent power, not just real power. Using VA per square foot lets you sum lighting with other loads on feeders and services while accounting for potential differences in power factor from different lighting types and ballasts. To apply it, multiply the area in square feet by the prescribed VA per square foot (for dwellings and listed occupancies this is the common approach). If you later need current, divide the total VA by the supply voltage. Amps per square foot isn’t used because it ties the calculation to voltage and power factor, and watts per square foot ignores reactive power, while kilovolt-amps per square foot is just another way of saying VA per square foot but is not the standard term used here.