4.3 Commercial & Multifamily Load Calculations (Article 220 Part III)

General Lighting Load by Occupancy (Table 220.12)

In the 2020 NEC, section 220.12 is titled Lighting Load for Non-Dwelling Occupancies and Table 220.12 is General Lighting Loads by Non-Dwelling Occupancy. The table was rebuilt around ASHRAE/IECC occupancy names, and dwelling units were taken out of it entirely — the 3 VA/sq ft dwelling figure now lives in 220.14(J). Some values fell and some rose, so never carry a 2017 number forward. Values worth being able to find in seconds:

The real table carries more rows than these — restaurants and clubs, schools, religious buildings, libraries, and others — and the exam is open-book, so read the value straight out of your own Table 220.12 instead of trusting a memorized figure. The footnotes carry as much weight as the numbers: they are what tell you a "store" is priced as retail and an "industrial commercial loft building" as manufacturing.

Floor area is taken from outside dimensions per 220.11, excluding open porches, garages, and unfinished spaces not adaptable for future use. The note to Table 220.12 states that the 125% continuous-load multiplier of 210.20(A) is already built into these unit loads, so do not apply it a second time. Under 220.12(B), a building designed and constructed to an adopted energy code may instead be calculated with the energy code's unit values, but only where a power monitoring system continuously reports the building's total general lighting load, an alarm annunciates if that load exceeds the energy-code values, the 220.42 demand factors are not applied, and the 125% continuous multiplier is applied.

Receptacle Load (220.14(I))

Non-dwelling receptacle outlets are calculated at not less than 180 VA per yoke [220.14(I)]. A duplex receptacle on one strap counts as 180 VA, not 360 VA. An assembly of four or more receptacles counts at 90 VA per receptacle.

Table 220.44 Demand Factors (Non-Dwelling Receptacles)

General-purpose receptacle loads and fixed multioutlet assemblies in non-dwelling occupancies may be reduced by Table 220.44:

Alternative: you may instead add receptacle VA to the general lighting load and apply Table 220.42 lighting demand factors to the combined total.

Worked Example — Receptacle Demand

150 receptacles × 180 VA = 27,000 VA. First 10,000 × 100% = 10,000; remaining 17,000 × 50% = 8500. Demand = 18,500 VA.

Continuous Loads at 125%

Commercial installations frequently have continuous loads (store lighting, signage, refrigeration). Per 210.19(A)(1) (conductors), 210.20(A) (overcurrent), and 215.2(A)(1) (feeders), size at 125% of the continuous portion. A 60A continuous lighting feeder needs 60 × 1.25 = 75A conductor and a 75A or larger breaker.

Motors, Signs, and Show Windows

• Motors: motor loads are calculated per 430.22 at 125% of the motor's full-load current rating (FLC) for continuous-duty motors. A feeder supplying a motor plus other loads adds the motor load at 125% plus the other loads at 100%.
• Sign outlets: 1200 VA per sign outlet [220.14(F)].
• Show windows: 200 VA per linear foot of show window [220.14(G)] — often a trap question because candidates forget to convert linear feet to VA.

Worked Example — Retail Store Service Load

A 5000 sq ft retail store on 120/208V three-phase, with 80 receptacles, a 5 hp motor (FLC 15.2A at 208V, or roughly 5500 VA), and 40 ft of show window. All lighting is LED track (continuous).

Step 1 — General lighting (Table 220.12, retail = 1.9 VA/sq ft): 5000 × 1.9 = 9500 VA (no extra 125% multiplier — the note to Table 220.12 says it is already inside the unit load)

Step 2 — Receptacles (220.14(I)): 80 × 180 = 14,400 VA

Apply Table 220.44: first 10,000 × 100% = 10,000; remaining 4400 × 50% = 2200. Demand = 12,200 VA.

Step 3 — Show window (220.14(G)): 40 ft × 200 VA/ft = 8000 VA

Step 4 — Motor (430.22, 125%): 5500 VA × 1.25 = 6875 VA

Step 5 — Total service load: 9500 + 12,200 + 8000 + 6875 = 36,575 VA

Step 6 — Convert to amps (208V three-phase, √3 = 1.732): 36,575 ÷ (208 × 1.732) = 36,575 ÷ 360.3 = 101.5 A → the next standard size in 240.6(A) is 110 A, so a 110A or 125A service.

Multifamily Dwellings (Standard Method)

Standard method for multifamily: calculate each unit individually per Part III (general lighting 3 VA/sq ft, small-appliance, laundry, appliances, dryer, range), then add common house loads (corridor lighting, parking, common laundry) calculated per Part III. Demand factors of 220.42 apply per unit; the optional 220.84 method (covered in 4.4) often yields a smaller building service when all units have electric cooking and HVAC.

Common Exam Traps

• Using 3 VA/sq ft for a commercial space — that's the dwelling value in 220.14(J). Commercial uses Table 220.12 by occupancy, and in the 2020 edition a store is retail at 1.9 VA/sq ft, not the old 3.
• Forgetting 125% on continuous commercial lighting and motors.
• Counting a duplex receptacle as 360 VA — it's 180 VA per yoke, not per opening.
• Forgetting show-window 200 VA/ft and sign 1200 VA/outlet.
• Mixing up Table 220.42 (lighting, 35% tier) with Table 220.44 (non-dwelling receptacles, 50% over 10 kVA).