8.6 Commercial and Industrial Load Calculations
Key Takeaways
- Table 220.56 applies commercial kitchen equipment demand factors of 100 percent for one or two units, 90 percent for three, 80 percent for four, 70 percent for five, and 65 percent for six or more, with the result never less than the sum of the two largest loads.
- NEC 220.14(K) requires bank and office building receptacle loads to be the larger of the 220.14(I) calculation after Table 220.44 demand factors, or 1 volt-ampere per square foot.
- NEC 220.43(B) requires 150 volt-amperes for every 2 feet or fraction thereof of lighting track in other than dwellings and hotel or motel guest rooms.
- NEC 220.87 permits an existing feeder or service load to be determined from the maximum demand recorded over a minimum 30-day period, multiplied by 125 percent, plus the new load.
- Continuous loads in commercial calculations attract the 125 percent multiplier when sizing conductors and overcurrent devices under 210.19, 210.20, 215.2, 215.3, and 230.42.
How Commercial Differs from Residential
Three structural differences drive commercial calculations:
- Receptacles are counted individually at 180 VA each — there is no 220.14(J) blanket inclusion.
- Most lighting is continuous, attracting the 125 percent multiplier at the conductor and overcurrent device.
- The demand factors are far less generous. Table 220.42 gives "all others" 100 percent; only hospitals, hotels, motels, and warehouses get a reduction on lighting.
Lighting
Use Table 220.12 for the occupancy type, applied to the floor area. Then check 220.42 — for most commercial occupancies the demand factor is 100 percent.
Because store, office, and warehouse lighting typically operates more than three hours, the lighting load is a continuous load under the Article 100 definition. That means the conductor and overcurrent device are sized at 125 percent of it under 210.19(A)(1), 210.20(A), 215.2(A)(1), and 215.3.
The 125 percent factor is not part of the Article 220 calculated load. It is applied afterward when sizing conductors and devices. Keep the two operations separate on the exam: Article 220 gives you the load; Articles 210, 215, and 230 tell you how to size for it.
Receptacles — 220.14(I), 220.44 and 220.14(K)
Step 1. Count receptacle outlets and multiply by 180 VA each (or 90 VA per receptacle for a listed assembly of four or more on one yoke).
Step 2. Apply Table 220.44: 100 percent of the first 10 kVA, 50 percent of the remainder.
Step 3. For banks and office buildings only, compare the result against 1 VA per square foot under 220.14(K) and use the larger.
Worked Example
An 8,000-square-foot office building has 96 duplex general-use receptacles on single yokes.
220.14(I): 96 x 180 VA = 17,280 VA
Table 220.44:
First 10,000 VA at 100% = 10,000 VA
Remaining 7,280 VA at 50% = 3,640 VA
---------
Calculated receptacle demand 13,640 VA
220.14(K) alternative: 8,000 ft2 x 1 VA = 8,000 VA
Use the LARGER = 13,640 VA
Commercial Kitchen Equipment — 220.56
It shall be permissible to calculate the load for commercial electric cooking equipment, dishwasher booster heaters, water heaters, and other kitchen equipment in accordance with Table 220.56. These demand factors shall be applied to all equipment that has either thermostatic control or intermittent use as kitchen equipment. These demand factors shall not apply to space-heating, ventilating, or air-conditioning equipment.
However, in no case shall the feeder or service calculated load be less than the sum of the largest two kitchen equipment loads.
| Number of units of equipment | Demand factor (percent) |
|---|---|
| 1 | 100 |
| 2 | 100 |
| 3 | 90 |
| 4 | 80 |
| 5 | 70 |
| 6 | 65 |
| 7 | 65 |
| 8–9 | 60 |
| 10 and over | 50 |
The floor rule is the part most often missed. If five units total 40 kW and the two largest are 15 kW and 12 kW, the 70 percent factor gives 28 kW — which is greater than 27 kW, so 28 kW governs. But if five units total 30 kW with the two largest at 12 kW each, 70 percent gives 21 kW, which is less than the 24 kW sum of the two largest, so 24 kW governs.
Restaurants — 220.88
220.88 New Restaurants. The calculated load for the service of a new restaurant may be determined from Table 220.88, which gives demand factors by total connected load and by whether the restaurant is all-electric or not. The table's demand percentages step down as connected load rises, from 80 percent at the low end to 50 percent above 325 kVA for all-electric restaurants.
The section states that the overall calculated load shall not be less than the sum of the largest two kitchen equipment loads — the same floor rule as 220.56.
Show Windows and Track Lighting
- 220.43(A) Show Windows. 200 volt-amperes per linear foot, measured horizontally along the base.
- 220.43(B) Track Lighting. 150 volt-amperes for every 2 feet or fraction thereof of lighting track, in other than dwelling units and hotel or motel guest rooms.
- 220.14(F) Sign and Outline Lighting. A minimum of 1200 volt-amperes for each required branch circuit specified in 600.5(A).
Worked Example — Track
A boutique installs 27 feet of continuous lighting track.
27 ft / 2 ft = 13.5, rounded up to 14 increments
14 x 150 VA = 2,100 VA
Motors and HVAC in the Service Calculation
220.50 Motors. Motor loads shall be calculated in accordance with 430.24, 430.25, and 430.26, and with 440.6 for air-conditioning and refrigerating equipment.
430.24 Several Motors or a Motor and Other Loads. Conductors supplying several motors, or a motor and other loads, shall have an ampacity not less than the sum of:
- 125 percent of the full-load current rating of the highest rated motor, plus
- the sum of the full-load current ratings of all the other motors in the group, plus
- the ampacity required for the other loads.
The 125 percent applies to only one motor — the highest rated. Everything else goes in at 100 percent.
220.51 covers fixed electric space heating at 100 percent, and 220.60 permits taking only the larger of two noncoincident loads such as heating and cooling.
Existing Loads — 220.87
A very practical section for renovation work:
The calculated load of a feeder or service shall be permitted to be determined by the maximum demand data if all of the following conditions are met:
- The maximum demand data is available for a 1-year period;
- The maximum demand at 125 percent plus the new load does not exceed the ampacity of the feeder or rating of the service;
- The feeder has overcurrent protection in accordance with 240.4, and the service has overload protection in accordance with 230.90.
Exception: If the maximum demand data for a 1-year period is not available, the calculated load shall be permitted to be based on the maximum demand — the highest average kilowatts reached and maintained for a 15-minute interval — continuously recorded over a minimum 30-day period using a recording ammeter or power meter connected to the highest loaded phase of the feeder or service, based on the initial loading at the start of the recording. The recording shall reflect the maximum demand of the feeder or service by being taken when the building or space is occupied and shall include by measurement or calculation the larger of the heating or cooling equipment load, and other loads that may be periodic in nature due to seasonal or similar conditions.
The practical routine is: record for 30 days, multiply the recorded maximum demand by 125 percent, add the new load, and compare against the existing service rating.
Feeder Neutral and Continuous Load
Two final reminders for commercial calculations:
- The grounded conductor is calculated separately under 220.61, covered in section 8.7.
- The 125 percent continuous-load multiplier applies to conductors and overcurrent devices, not to the Article 220 calculated load itself. A question that asks for "the calculated load" wants the Article 220 number; a question that asks for "the minimum conductor ampacity" wants the 125 percent version.
A commercial kitchen has six units of thermostatically controlled equipment totaling 48 kW, with the two largest rated 14 kW and 11 kW. What is the calculated demand load under NEC 220.56?
A restaurant installs 33 feet of continuous lighting track. What load must be included under NEC 220.43(B)?
Under NEC 430.24, how is the conductor ampacity determined for a feeder supplying four motors of 20, 15, 12, and 8 amperes full-load current?
Under the exception to NEC 220.87, what recording period and multiplier are used to determine an existing load when one year of demand data is unavailable?