4.6 Non-Dwelling Load Calculation Workshop (0302)

The Order of Operations

A commercial load calculation goes wrong far more often from sequence than from arithmetic. Fix the order in your head and the problems become mechanical:

1. General lighting — floor area × the unit load from Table 220.42(A).
2. Specific lighting loads — show windows, track lighting, and signs, each with their own rule.
3. Receptacles — 180 VA per strap (220.14(I)).
4. Specific equipment — kitchen equipment, motors, HVAC, water heaters, each under its own article.
5. Apply demand factors — Table 220.45 for lighting (only four occupancy families get one), 220.44 for receptacles, 220.56 for commercial kitchen equipment.
6. Apply the 125% continuous adder to the continuous portion — last, after demand factors.
7. Convert to amperes, select the overcurrent device from 240.6(A), then select conductors and check 110.14(C).

Step 6 is the one to watch. The 125% factor multiplies the continuous load, and a demand factor is a separate reduction applied to a specific category. Applying 125% before a demand factor, or applying a demand factor to a load that does not get one, are the two errors that show up most in practice sets.

The Specific Lighting Rules

Show-window lighting is a favorite exam item because it is measured per linear foot of window, not per fixture and not per square foot. A 20 ft show window is 20 × 200 = 4000 VA whether it holds two floodlights or twenty.

Commercial Kitchen Equipment — 220.56

Where a feeder or service supplies commercial electric cooking equipment, dishwasher boosters, water heaters, and other kitchen equipment, 220.56 permits a demand factor based on the number of units:

There is one hard floor: the feeder or service demand load shall not be less than the sum of the two largest kitchen equipment loads. If applying 65% to six units drops you below the sum of the two biggest ones, you use the sum of the two biggest ones instead. Space-heating, ventilating, and air-conditioning equipment is not included in this demand — it is calculated separately.

Worked Calculation — A 3,000 ft² Restaurant

A restaurant occupies 3,000 ft², served at 208Y/120 V, three phase. Inventory:

• General lighting, operating more than 3 hours (continuous)
• A 15 ft show window, continuous
• 24 ft of lighting track in the dining room, continuous
• One required sign outlet, continuous
• 40 general-purpose receptacle straps, non-continuous
• Kitchen equipment: a 12 kVA range, a 9 kVA fryer, a 6 kVA dishwasher booster, a 5 kVA steam table, and a 4 kVA warming cabinet — five units, non-continuous

Step 1 — General lighting

Table 220.42(A): restaurants are 2 VA/ft². 3,000 × 2 = 6,000 VA. Restaurants are not in Table 220.45, so they fall under "All others" at 100% — no reduction. Continuous.

Step 2 — Specific lighting loads

• Show window: 15 ft × 200 VA = 3,000 VA, continuous
• Track lighting: 24 ft ÷ 2 = 12 units × 150 VA = 1,800 VA, continuous
• Sign outlet: 1,200 VA minimum, continuous

Step 3 — Receptacles

40 straps × 180 VA = 7,200 VA. Apply 220.44: the first 10 kVA at 100% covers all of it, so 7,200 VA, non-continuous.

Step 4 — Kitchen equipment with the 220.56 demand

Connected: 12 + 9 + 6 + 5 + 4 = 36 kVA across five units. Demand factor for five units is 70%: 36,000 × 0.70 = 25,200 VA.

Check the floor: the two largest loads are 12 kVA and 9 kVA, summing to 21,000 VA. Our demand load of 25,200 VA is larger, so the demand result stands. (Had the mix been six small units, the floor would have governed.)

Step 5 — Total, with the continuous adder applied last

Step 6 — Amperes, device, and conductor

I = 47,400 ÷ (1.732 × 208) = 47,400 ÷ 360.3 = 131.6 A

• Overcurrent device: the next standard rating at or above 131.6 A per 240.6(A) is 150 A.
• Conductors: ampacity of at least 131.6 A. From Table 310.16, 1/0 AWG copper at 75 °C is 150 A — comfortably above the calculated load and matched to the 150 A device.
• Terminations: the equipment is rated over 100 A, so 110.14(C) puts us in the 75 °C column, which is the column already used.

Sanity check the answer. 47,400 VA in a 3,000 ft² restaurant is about 16 VA/ft², which is a believable number for food service. If a calculation lands at 4 VA/ft² for a restaurant or 40 VA/ft² for an office, a demand factor was applied where none belonged or a unit load came out of the wrong row.