Cooking Calculations    Page 4



ANSWERS TO THE PRACTICE QUESTIONS:


1. 8 kW

2. 35 kW

3. 58.75 kW

4. 25 kW

5. 66.25 kW

Please be sure to send me an email or write down any questions that you have so I can help you explore an answer. 

BRADY BUNCH: NOTE 3 Calculations

Not all cooking equipment is a range. Often times we have cooktops mounted in islands and wall mounted ovens and many other configurations. I first saw this type of cooking equipment as a young boy while watching the Brady Bunch so I like to refer to the rules for sizing this equipment as the Brady Bunch Rules. The purpose of doing a load calculation is to reduce the size of the main service to a safe and affordable size. Many times when we are working with these smaller, individual units, the normal process will end up increasing the load size. So, an optional note was added to Table 220.55 to allow us to still squeeze the load in these circumstances. NOTE 3 to Table 220.55


Table 220.55, Note 3: Over 1-3/4 kW through 8-3/4 kW. In lieu of the method provided in Column C, it shall be permissible to add the nameplate ratings of all ranges rated more than 1-3/4 kW but not more than 8-3/4 kW and multiply the sum by the demand factors specified in Column A or B for the given number of appliances.

Here we are going to use Columns A and B. This is the only time we use these columns in Table 220.55. Please note that Column C lists numbers in kilowatts. Columns A and B list numbers in a percentage, NOT kilowatts. Note 3 tells us we are to squeeze the appliances by ratings. So all cooking equipment rated over 1.75 kW but less than 3.5 kW we will use the values in Column A. The writing in the NEC is intended to be very specific and avoid interpretation. Please notice......less than 3.5 kW is very specific. It does not include 3.5 kW. If the NEC wanted to include 3.5 kW it would have written it as 1.75 kW to 3.5 kW. 

Column B is used for appliances that are 3.5 kW but not more than 8.75 kW. 

Step 1: Total the nameplate ratings of all cooking 
             appliances in the appropriate Columns. 
Step 2: Multiply sum by the demand factor of   
    Column A or B.

Column A = over 1-3/4 kW but less than 3-1/2 kW

Example: What is the demand  load of two ovens rated 
   3 kW each?


Step 1: Add the nameplate values, 2 units x 3 kW = 6 kW
Step 2: Multiply sum by demand factor. (The percentage listed in Column A)

Table 220-55, Column A = 2 units = 75% demand factor

(2 units x 3 kW per unit) x .75 demand factor = 4.5  kW
    
Net computed load (demand load) = 4.5 kW

Example: Ten cooktops rated 2 kW each.

Table 220.55, Column A= 49% demand factor for ten units

10 units x 2 kW each x .49 demand factor = 9.8 kW

Demand load = 9.8 kW

The same process is used for both Column A and Column B. If you have a mixture of cooking appliances and some are in the range of Column A and some are in the range of Column B. You simply complete the process for Column A, then complete the process for Column B, then add the two answers together to achieve the total. 


Find the net computed load of the following:

A. 6 cooktops rated at 3 kW each

B. 8 ovens rated at 2.5 kW each

C. 4 ranges at 6 kW each

D. 15 cooktops each at 3.7 kW

E . 20 ovens each at 4 kW

ted 11.99kW

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