6.4 Commercial & Industrial Feeder/Service Calculations
Key Takeaways
- Commercial lighting unit loads under NEC Table 220.12 (e.g., retail stores at 1.9 VA/sq ft, offices at 1.3 VA/sq ft, restaurants at 1.5 VA/sq ft) are standardly continuous loads requiring a 125% branch circuit and feeder multiplier.
- Show window lighting must be calculated under NEC 220.14(G) and 220.43(A) at not less than 200 VA per linear foot (660 VA/m) measured along its base.
- Each commercial occupancy accessible to pedestrians requires at least one 20A sign/outline lighting branch circuit calculated at a minimum of 1,200 VA under NEC 220.14(F) and 600.5 (sized at 1,500 VA continuous).
- Commercial receptacle loads are computed under NEC 220.14(I) at 180 VA per yoke/strap and derated under Table 220.44 at 100% for the first 10 kVA and 50% for all remaining kVA.
- Commercial kitchen electric cooking equipment is subject to Table 220.56 demand factors (1-2 units = 100%, 3 units = 90%, 4 units = 80%, 5 units = 70%, 6+ units = 65%), but the total demand can never be less than the sum of the two largest units.
6.4 Commercial & Industrial Feeder/Service Calculations
Unlike residential installations, commercial and industrial occupancies feature substantial continuous lighting, specialized display window loads, dedicated exterior signage, high-density receptacle layouts, three-phase commercial kitchen cooking appliances, and heavy motor equipment.
Designing commercial services requires applying the specific rules in NEC Article 220 Parts II and III alongside three-phase power mathematics.
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| COMMERCIAL LOAD CALCULATION ARCHITECTURE |
| |
| [1. CONTINUOUS LIGHTING (Table 220.12 & 220.18)] |
| - Sq Ft x Table 220.12 VA/sq ft x 125% (Continuous Load Multiplier) |
| |
| [2. SHOW WINDOWS (NEC 220.14(G) & 220.43(A))] |
| - Linear Feet x 200 VA/linear ft x 125% (Continuous Load Multiplier) |
| |
| [3. COMMERCIAL OUTLINE / SIGN LIGHTING (NEC 220.14(F) & 600.5)] |
| - Minimum 1,200 VA per commercial tenant entrance x 125% = 1,500 VA |
| |
| [4. GENERAL RECEPTACLES (NEC 220.14(I) & Table 220.44)] |
| - Number of Yokes/Straps x 180 VA -> 1st 10 kVA @ 100% + Remainder @ 50% |
| |
| [5. COMMERCIAL KITCHEN COOKING EQUIPMENT (NEC Table 220.56)] |
| - Sum all kitchen equipment -> Apply Table 220.56 demand factor (65%-100%)|
| |
| [6. HVAC & MOTOR LOADS (NEC 220.60, 430.24)] |
| - Noncoincident HVAC (larger of AC vs. Heat) + 25% of largest motor FLC |
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1. Commercial Lighting Loads (NEC Table 220.12 & Continuous Rule)
Commercial occupancies require minimum general lighting unit loads per square foot under NEC Table 220.12.
Table 220.12 Representative Commercial Unit Loads
| Occupancy Type | Unit Load (VA/sq ft) | Continuous Multiplier (125%) | Total Feeder Design VA/sq ft |
|---|---|---|---|
| Office Buildings | 1.30 VA/sq ft | x 1.25 | 1.625 VA/sq ft |
| Retail Stores | 1.90 VA/sq ft | x 1.25 | 2.375 VA/sq ft |
| Restaurants | 1.50 VA/sq ft | x 1.25 | 1.875 VA/sq ft |
| Warehouses (Storage) | 0.25 VA/sq ft | x 1.25 | 0.313 VA/sq ft |
| Hospitals | 1.60 VA/sq ft | x 1.25 | 2.000 VA/sq ft |
| Hotels and Motels | 1.40 VA/sq ft | x 1.25 | 1.750 VA/sq ft |
| Banks | 1.40 VA/sq ft | x 1.25 | 1.750 VA/sq ft |
| Schools / Universities | 1.20 VA/sq ft | x 1.25 | 1.500 VA/sq ft |
[!NOTE] Continuous Lighting Rule: In commercial occupancies, general lighting is standardly energized for 3 hours or more continuously. Therefore, under NEC 210.20(A) and 215.3, branch circuit overcurrent protection and feeder conductors must be sized at 125% of the calculated lighting load.
2. Show Window & Commercial Sign Loads
Show Window Lighting (NEC 220.14(G) & 220.43(A))
Show windows used for retail merchandise display must be calculated at not less than 200 VA per linear foot (660 VA/m), measured horizontally along the base of the window.
Connected Show Window VA = Linear Feet x 200 VA/ft Continuous Design VA = Linear Feet x 200 VA/ft x 1.25
Sign and Outline Lighting (NEC 220.14(F) & 600.5)
Under NEC 600.5(A), each commercial building and each commercial occupancy accessible to pedestrians must be provided with at least one outlet for sign or outline lighting on a dedicated 20A branch circuit. The branch circuit load must be calculated at a minimum of 1,200 VA (or actual rating of connected sign equipment). Sized as a continuous load:
Sign Circuit Load = 1,200 VA x 1.25 = 1,500 VA
3. Commercial Receptacle Loads & Demand Factors (NEC 220.14(I) & Table 220.44)
In non-dwelling occupancies, convenience receptacle outlets are calculated separately from lighting:
- Individual Receptacles: Each single or multi-receptacle device mounted on a single yoke/strap is calculated at not less than 180 VA (NEC 220.14(I)).
- Duplex Receptacle: Mounted on one yoke = 180 VA.
- Triplex Receptacle: Mounted on one yoke = 180 VA.
- Quadruplex (Two Duplexes on 2 yokes): Mounted on two yokes = 2 x 180 = 360 VA.
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| NEC TABLE 220.44 RECEPTACLE FEEDER DEMAND FACTORS |
| |
| TOTAL CONNECTED RECEPTACLE LOAD = Total Yokes x 180 VA |
| |
| PORTION OF RECEPTACLE LOAD | DEMAND FACTOR | CALCULATION METHOD |
| ----------------------------------+---------------+------------------- |
| First 10 kVA (10,000 VA) or less | 100% | First 10,000 VA x 1.00|
| Remainder over 10 kVA (10,000 VA) | 50% | (Load - 10,000) x 0.50|
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Example: An office building contains 150 duplex receptacles on single yokes:
- Total Connected Load = 150 x 180 VA = 27,000 VA = 27 kVA.
- First 10,000 VA x 1.00 = 10,000 VA.
- Remaining 17,000 VA x 0.50 = 8,500 VA.
- Net Feeder Receptacle Demand Load = 10,000 + 8,500 = 18,500 VA. (Compared to 27,000 VA connected, saving 8.5 kVA in service capacity).
4. Commercial Kitchen Cooking Equipment (NEC Table 220.56)
In commercial kitchens (restaurants, cafeterias, hotels, institutional dining), electric cooking equipment—including fryers, griddles, ovens, steamers, microwave ovens, booster heaters, and commercial dishwashers—is subject to the demand factors in NEC Table 220.56.
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| NEC TABLE 220.56 COMMERCIAL KITCHEN EQUIPMENT DEMAND |
| |
| NUMBER OF COMMERCIAL UNITS | DEMAND FACTOR (PERCENT OF NAMEPLATE) |
| ----------------------------------+------------------------------------- |
| 1 to 2 Units | 100% |
| 3 Units | 90% |
| 4 Units | 80% |
| 5 Units | 70% |
| 6 or More Units | 65% |
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[!IMPORTANT] The Minimum Floor Rule for Kitchen Demand: Under NEC 220.56, in no case shall the feeder demand load calculated under Table 220.56 be less than the sum of the nameplate ratings of the two largest kitchen equipment items.
5. Three-Phase Power Formulas & Calculations
Commercial services are overwhelmingly 3-phase, 4-wire wye systems (208Y/120V or 480Y/277V). Sizing service conductors requires the three-phase current formula:
I_Line = Total 3-Phase Volt-Amperes / (√3 x V_Line-to-Line) = Total VA / (1.732 x V_Line)
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| THREE-PHASE CURRENT DIVISOR CONSTANTS |
| |
| * For 208Y/120V 3-Phase Systems: |
| Divisor = 1.73205 x 208V = 360.27 |
| Line Current (Amperes) = Total VA / 360.27 |
| |
| * For 480Y/277V 3-Phase Systems: |
| Divisor = 1.73205 x 480V = 831.38 |
| Line Current (Amperes) = Total VA / 831.38 |
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6. Complete Worked Example: Commercial Restaurant Service (208Y/120V 3-Phase)
Building Specifications:
- Occupancy: Commercial Restaurant with Bar
- Floor Area: 3,600 sq ft
- Show Window: 25 linear feet
- Sign: One outdoor sign circuit
- Receptacles: 60 duplex receptacles on single yokes
- Commercial Kitchen Cooking Equipment:
- Electric Fryer: 12.0 kW
- Convection Oven: 8.5 kW
- Electric Griddle: 6.0 kW
- Dishwasher with Booster Heater: 9.5 kW
- Steam Table: 4.0 kW
- Commercial Microwave: 2.0 kW (Total 6 kitchen units, sum of nameplates = 42.0 kW = 42,000 VA)
- HVAC & Motors (3-Phase 208V):
- Rooftop Air Conditioning Unit: 15.0 kVA
- Gas Heating Unit with Blower: 3.0 kVA
- Walk-in Cooler Compressor (Largest Motor): 4.8 kVA
- Walk-in Freezer Compressor: 3.6 kVA
- Kitchen Exhaust Hood Make-up Air Fan: 2.4 kVA
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COMMERCIAL RESTAURANT SERVICE CALCULATION SHEET
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1. GENERAL LIGHTING LOAD (NEC Table 220.12 & Continuous Rule)
- Baseline Load = 3,600 sq ft x 1.5 VA/sq ft = 5,400 VA
- Continuous Multiplier (125%): 5,400 VA x 1.25 = 6,750 VA
>>> NET LIGHTING LOAD = 6,750 VA
2. SHOW WINDOW LIGHTING (NEC 220.14(G) & 220.43(A))
- 25 linear feet x 200 VA/ft = 5,000 VA
- Continuous Multiplier (125%): 5,000 VA x 1.25 = 6,250 VA
>>> NET SHOW WINDOW LOAD = 6,250 VA
3. SIGN LIGHTING (NEC 220.14(F) & 600.5)
- 1 Sign Circuit @ 1,200 VA x 1.25 continuous = 1,500 VA
>>> NET SIGN LOAD = 1,500 VA
4. GENERAL RECEPTACLES (NEC 220.14(I) & Table 220.44)
- 60 yokes x 180 VA/yoke = 10,800 VA
- Apply Table 220.44 Demand Factors:
* First 10,000 VA @ 100% = 10,000 VA
* Remaining 800 VA (10,800 - 10,000) @ 50% = 400 VA
>>> NET RECEPTACLE DEMAND LOAD = 10,400 VA
5. COMMERCIAL KITCHEN EQUIPMENT (NEC Table 220.56)
- Total Connected Load (6 units) = 42,000 VA
- Table 220.56 Demand Factor for 6 units: 65%
- Calculated Demand = 42,000 VA x 0.65 = 27,300 VA
- Minimum Check (Sum of 2 largest units):
Fryer (12.0 kW) + Dishwasher (9.5 kW) = 21.5 kW = 21,500 VA
Since 27,300 VA > 21,500 VA, 27,300 VA applies.
>>> NET COMMERCIAL KITCHEN LOAD = 27,300 VA
6. NONCOINCIDENT HVAC & MOTOR LOADS (NEC 220.60 & 430.24)
- Noncoincident HVAC: 15.0 kVA AC vs. 3.0 kVA Heat = 15,000 VA (AC selected)
- Other Motors:
* Walk-in Cooler (Largest Motor) = 4,800 VA
* Walk-in Freezer Motor = 3,600 VA
* Exhaust Hood Fan Motor = 2,400 VA
- Motor 25% Addition for Largest Motor (Cooler):
4,800 VA x 0.25 = 1,200 VA
- Subtotal Motors & HVAC = 15,000 + 4,800 + 3,600 + 2,400 + 1,200 = 27,000 VA
>>> NET HVAC & MOTOR LOAD = 27,000 VA
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TOTAL COMMERCIAL SERVICE LOAD SUMMARY
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1. Lighting Load (125% Continuous) = 6,750 VA
2. Show Window (125% Continuous) = 6,250 VA
3. Sign Lighting (125% Continuous) = 1,500 VA
4. Receptacle Load (Table 220.44 Demand) = 10,400 VA
5. Kitchen Equipment (Table 220.56 65% Demand) = 27,300 VA
6. HVAC, Refrigeration & Motors (with 25% addition) = 27,000 VA
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TOTAL CALCULATED 3-PHASE LOAD = 79,200 VA (79.2 kVA)
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7. THREE-PHASE SERVICE CURRENT & SIZING (208Y/120V 3-PHASE)
- Line Current: I = 79,200 VA / (1.732 x 208V) = 79,200 / 360.27 = 219.83 Amperes
- Next Standard Main OCPD Rating (NEC 240.6(A)) = 225 Amperes or 250 Amperes
- Minimum 75°C Copper Service Conductors (NEC Table 310.16):
* For 250A Service: 250 kcmil Copper THHN/THWN (Rated 255A @ 75°C)
A commercial retail boutique has 40 linear feet of exterior show window. What is the minimum calculated continuous branch circuit load that must be allocated for this show window under NEC 220.14(G) and 220.43(A)?
An office building contains 120 duplex convenience receptacle outlets mounted on individual single yokes. Under NEC 220.14(I) and Table 220.44, what is the net calculated receptacle feeder demand load?
A commercial restaurant kitchen contains five (5) electric cooking appliances with nameplate ratings of 10 kW, 8 kW, 6 kW, 5 kW, and 4 kW (total connected load = 33 kW). What is the minimum calculated feeder demand load under NEC Table 220.56?