6.4 Commercial Lighting, Receptacle, Sign & Show-Window Loads (Table 120.42(A) & 120.44)

Commercial calculations on the exam

DLI's knowledge areas include commercial load calculations. Expect a building area, an occupancy type, and a list of receptacles, signs, show windows, and equipment. Build the load line by line, apply only the demand factors the Code allows, and convert to amperes with the correct voltage formula.

General lighting (120.42 and Table 120.42(A))

Multiply the floor area (outside dimensions, 120.5(C)) by the unit load for the occupancy:

Table 120.45 demand factors then apply: 100% for most occupancies, with reductions only for dwellings, hotels and motels, and warehouses (first 12,500 VA at 100%, remainder at 50%). Section 120.42(B) allows a building designed to an adopted energy code to use the energy code's lighting power values under specific conditions, such as a power monitoring system.

Receptacles and outlets (120.14)

Section 600.5(A) requires at least one sign outlet at each entrance to each tenant space of commercial buildings accessible to pedestrians, supplied by a branch circuit rated at least 20 A that supplies no other load.

Receptacle demand (Table 120.44)

Receptacle loads calculated at not more than 180 VA per outlet may be reduced:

Converting to amperes

• Single-phase 120/240 V: $I = \text{VA} \div 240$
• Three-phase: $I = \text{VA} \div (E \times 1.732)$, such as $\text{VA} \div 360.3$ at 208 V or $\text{VA} \div 831.4$ at 480 V

Worked example: retail store

A 20,000 ft² retail store has 100 general-purpose receptacles, 60 linear feet of show window, and one sign outlet, supplied at 208Y/120 V, three-phase.

Feeder current: $65{,}200 \div (208 \times 1.732) = 65{,}200 \div 360.3 = 181$ A. Conductor and OCPD sizing then apply 215.2 and 215.3 (or 230.42 for a service) to the continuous loads, together with any HVAC, motor, and equipment loads that a full calculation would add.

Worked example: office receptacles

A 15,000 ft² office has 60 general-purpose receptacles.

1. Calculated: $60 \times 180 = 10{,}800$ VA; with Table 120.44: $10{,}000 + 800 \times 0.5 = 10{,}400$ VA.
2. Minimum: $15{,}000 \times 1 = 15{,}000$ VA.
3. Use the larger value: 15,000 VA.