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The calculation to determine service load for several household cooking appliances is full of rules which make a significance difference in the result. A careful reading of these rules in NEC220 will be necessary to correctly solve for service loads of these appliances.

Now, I know no electrician is ever going to be called upon to make this sort of calculation. Yet this calculation seems to be included on every Journeyman and Master license exam I have ever seen. So let's get to it.

There are three columns in the table. 

Column A id for small appliances. If all the appliances you are calculating are less than 3.5kW then find the percentage which corresponds to number of appliances and multiply this percentage times the total nameplate for all appliances. The result is the demand.

Column B. If the appliances you are calculating are from 3.5kW to 8.75kW, same deal. Find the total nameplate then multiply by the percentage you find for the number of appliances on the service.

Column C. This is the difficult one. There are a few rules which guide you through this column.

    If there are several ranges which are over 12kW, and all are the same, then increase column C by 5% for each kW or major fraction .5 they exceed 12kW. The audio support explains this with examples. Listen as needed to the audio support for these pages.

    If there is a mixture of cooking appliances, with even one less than 12kW, still use column C but enter any that are less then 12kW as 12kW and find the average. Then increase Column C by 5% for each kW or major fraction .5 the average is above 12kW.

Here are links to practice problems and audio support by page number for each:

Column A Lookups    159
Column B or C Calculation    159
Note 1    160
Note 2    161
Weird Combinations    162

Story Problems    163    164    165    166

Find audio support by page number depending on your interest.

159    160    161    162    163    164    165    166



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