Commercial Kitchen Load Calculation per NEC 220.56

Why Accurate Commercial Kitchen Load Calculation is Critical

Performing a precise electrical load calculation for a commercial kitchen is one of the most important responsibilities for an installing electrician. An undersized service can lead to overloaded circuits, tripping breakers, and significant fire hazards. Conversely, a drastically oversized service results in unnecessary expenses for the client, including higher costs for switchgear, conductors, and conduit, such as for a large 200 amp panel or greater. Following the guidelines in the NEC code book, specifically Article 220, Part IV, ensures the system is both safe and cost-effective. These calculations form the backbone of proper feeder and service calculations, safeguarding the entire electrical infrastructure.

Understanding NEC 220.56: The Core of Kitchen Equipment Load Calculation

NEC Section 220.56 provides a specific, permissible method for calculating the demand load for commercial kitchen equipment. This includes items like commercial electric cooking equipment, dishwasher booster heaters, water heaters, and other appliances characterized by thermostatic control or intermittent use. The logic behind this section is that in a busy kitchen, it is highly unlikely that every single piece of equipment will be running at its maximum rated capacity at the same exact moment. Some ovens will be cycling on and off, fryers will be at temperature, and certain mixers will be used only periodically. NEC Table 220.56 provides a demand factor based on the number of equipment units, allowing for a realistic, reduced load calculation that reflects actual usage. Understanding this principle is a frequent topic on exams, making it critical knowledge for anyone pursuing our Master Electrician exam prep study plan.

Key Definitions for Your Calculation

Before diving into the calculation, it’s essential to understand a few key terms that are central to the process:

• Nameplate Rating: This is the full electrical rating of a piece of equipment as specified by the manufacturer, usually found on a metal tag on the device. It provides voltage, amperage or wattage, and phase.
• Full-Load Amps (FLA): The current a motor draws when operating at its rated horsepower and voltage. This is a critical value for motor load calculations.
• Continuous Load: A load where the maximum current is expected to continue for three hours or more, such as commercial lighting. The NEC requires these loads to be calculated at 125% for branch circuits and feeders.
• Single-Phase vs. Three-Phase Power: Commercial kitchens often use a mix of power types. Single-phase power is typical for smaller appliances and lighting, while larger equipment like convection ovens and large mixers often require three-phase power for greater efficiency. Properly accounting for both is vital. For more complex scenarios, our guide on three-phase calculations offers an in-depth look.

Step-by-Step Guide to Commercial Kitchen Load Calculation Using Table 220.56

Follow this structured process to ensure your calculations are accurate and compliant with the NEC.

1. List All Kitchen Equipment: Begin by creating a complete inventory of every piece of electrical kitchen equipment that falls under the scope of 220.56. This list should only include equipment with thermostatic control or intermittent use (e.g., cooking appliances, booster heaters, food warmers). General purpose motor loads, such as on mixers or grinders, may need to be calculated separately per other NEC sections like 220.50. Do not include HVAC or general ventilation fans in this list. For each item, record its nameplate rating in kW or kVA.
2. Sum the Nameplate Ratings: Add the ratings of all the inventoried equipment to get the total connected kitchen equipment load.
3. Apply the Demand Factor from NEC Table 220.56: Consult Table 220.56 in your NEC code book. Find the row corresponding to the total number of equipment units from your list. The table provides a demand factor percentage. For one or two pieces of equipment, the demand factor is 100%. For six pieces, it drops to 65%.
4. Calculate the Preliminary Demand Load: Multiply the total connected load (from Step 2) by the demand factor percentage (from Step 3). This gives you the preliminary demand load.
5. Perform the “Two Largest Loads” Check: NEC 220.56 includes a critical final check: the calculated feeder or service load shall not be less than the sum of the two largest kitchen equipment loads. Compare your result from Step 4 with the sum of the two largest individual loads. You must use whichever value is greater.
6. Incorporate Other Loads: The value from Step 5 is only for the kitchen equipment. You must still perform separate feeder and service calculations for all other loads per NEC Article 220. This includes general lighting, receptacle loads (calculated at 180VA per outlet yoke for commercial spaces), motor loads for ventilation, and any continuous load at 125%.
7. Determine Final Service Size: Combine the final kitchen demand load with all other calculated loads to arrive at the total demand for the establishment. This final amperage value determines the required service size and influences everything from wire size computation to overcurrent protection.

Example Calculation in Practice

Let’s consider a small commercial kitchen with 6 pieces of equipment:

• Convection Oven: 15 kW
• Deep Fryer 1: 14 kW
• Deep Fryer 2: 14 kW
• Food Warmer: 3 kW
• Dishwasher: 7 kW
• Salamander Broiler: 4 kW

Step 1 & 2: The total connected load is 15 + 14 + 14 + 3 + 7 + 4 = 57 kW.

Step 3: There are 6 units of equipment. According to Table 220.56, the demand factor for 6 units is 65%.

Step 4: The preliminary demand load is 57 kW * 0.65 = 37.05 kW.

Step 5: The two largest loads are the oven (15 kW) and a fryer (14 kW). Their sum is 15 + 14 = 29 kW. Since 37.05 kW is greater than 29 kW, we use 37.05 kW as our kitchen equipment demand load.

This final value is then used alongside other loads to size the service. Tools like an ampacity chart and a voltage drop calculator are essential at this stage to select the correct conductors.

Important Considerations and Common Mistakes

Even experienced electricians can make errors. Keep these key points in mind to ensure your commercial kitchen load calculation is flawless.

• Noncoincident Loads (NEC 220.60): In some cases, you may have loads that are interlocked so they cannot run at the same time, such as a primary and backup piece of equipment. According to NEC 220.60, you are permitted to omit the smaller of the two loads from the calculation.
• Appliance Outlet Centers: The 2023 NEC has specific rules for commercial appliance outlet centers (CAOCs). Understanding how CAOCs are installed is crucial as they become more common in modern kitchens.
• Receptacle Placement and Loads: General receptacle loads are calculated separately, but their placement is also governed by code. A common error is failing to account for specific countertop receptacle requirements. For a refresher, review our article on NEC kitchen receptacle placement.
• Clarifying the 125% Continuous Load Rule: The 125% multiplier for a continuous load is generally not applied to individual kitchen equipment loads before using Table 220.56. This is because most equipment that qualifies (items with thermostatic control) is considered non-continuous. The demand factor is applied directly to the sum of nameplate ratings. Do not apply the 125% rule to the entire group of kitchen equipment loads or to the final demand load calculated from the table.

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Frequently Asked Questions (FAQ)

What is the difference between total connected load and demand load for a commercial kitchen?

The total connected load is the sum of the nameplate ratings of all equipment as if they were running simultaneously. The demand load is a smaller, more realistic value calculated using the demand factor from NEC Table 220.56, which accounts for the fact that not all equipment is used at once.

Can I use NEC Table 220.56 for residential kitchen equipment load?

No. Table 220.56 is exclusively for commercial and institutional kitchens. Residential cooking appliance loads are calculated using NEC 220.55, which has different demand factors.

Does NEC 220.56 apply to branch circuits or only feeder and service calculations?

NEC 220.56 is used for sizing feeders and services that supply multiple pieces of kitchen equipment. Individual branch circuit conductors and overcurrent protection must be sized to handle the load of the specific appliance they serve, often at 125% if it’s considered a continuous load.

Where can I find online electrical courses to better understand the NEC code book?

ExpertCE offers a wide range of state-approved online electrical courses designed to help electricians at all levels, from apprentices to journeyman and master electricians, deepen their understanding of the NEC and stay current with code changes.

Primary Sources

• NFPA 70, National Electrical Code (NEC), Article 220