Cooking Calculations

Written By Ted Smith 12/5/2015
The "Smitty" Translation

The above is the official way of writing the following:

Cooking equipment that has a nameplate rating that is greater, but not including, 1.75kW has a very small chance of operating at full nameplate rating for any length of time....SO... we do not have to account for the total nameplate rating. We can calculate it at an amount that is less. How much less? We will learn that over the next few pages. The method for determining how much less will come from Table 220.55 and the Notes to the table. 

Cooking equipment that has a nameplate rating that is 1.75kW or less does not use a lot of power. They are very small and for the most part have only two settings, off and on. A good example of this type of appliance is a built-in warming drawer.  
These appliances use their full nameplate every time they are turned on. We have to calculate these appliances at their full nameplate rating. Sometimes it is misunderstood and interpreted that these type of appliances are not included in a load calculation. That is not correct. We include them if they are permanently hard-wired in place, we just don't squeeze their loads when calculating the demand. 

Remember: You must never use these appliances in conjunction with Table 220.55. These appliances' demand will be added to the cooking equipment demand, at 100%, after all, other calculations have been completed. 

 
Welcome to this module in the Durbin's Learning system. We are going to introduce you today to the calculations required by the NEC 2017 to determine feeder and branch circuit loads for cooking equipment in a dwelling. 

Upon completion of this module you will be able to :

1. Determine the demand on a dwellings service of the cooking appliances
2. Determine the demand for large cooking appliances rated 12.1kW to 27kW
3. Determine the demand for medium cooking appliances rated 8.75kW through 12 kW
4. Determine the demand for small cooking appliances rated less than 8.75kW
5. Determine the demand on the branch circuit feeder for all of the above type cooking appliances
6. Determine the demand for cooking appliances used for instructional purposes. 

You will also be very familiar and comfortable with using Table 220.55 of the NEC. 

Note that this module was written according to the 2017 edition of the NEC.
 

DEFINITIONS

For the purposes of this module, all household cooking appliances are assumed to be single phase, 240V appliances on single-phase services. 

These are some of the terminologies you will encounter in this module. 

Nameplate Rating: The nameplate rating of electric ranges and other cooking appliances is the maximum power the unit will use if all the elements are turned on and set on high. 

Demand: Demand is the amount of power an appliance will utilize and the minimum rating required for the feeder and equipment supplying power to the appliance. Demand is measured in volt-amps. 

Demand Factor: It is unlikely that appliances will operate at their full nameplate and demand for any length of time. The NEC allows us to size feeders and equipment supplying power below the total nameplate and demand. A demand factor is an amount we are allowed to reduce the demand for purposes of sizing feeders and equipment used to supply power.

Cooking Appliances: A cooking appliance is an appliance that is used to cook food and is permanently mounted. Items such as ranges, ovens, cooktops and built-in microwaves or food warmers are all considered cooking equipment.


You should have a copy of the 2017 NEC, paper, pencil and calculator ready as you complete this module. 

Article 220.55 Electric Ranges and Other Cooking Appliances- Dwelling Unit(s)- The demand load for household electric ranges, wall-mounted ovens, counter-mounted cooking units, and other household cooking appliances individually rated in excess of 1 3/4 kW shall be permitted to be computed in accordance with Table 220.55.