National Electrical Installation Standards

Standards as High as Your Own

Tuesday, September 19, 2023


Hello Charlie, I am a Junior Engineer, so I am sorry if this is a bad question. Are the demand factors mentioned in Article 220 Part III and Part IV required? I'm under the impression that I can choose my own demand factors since it is stated in Section 220.40, that the demand factors are "permitted" for both Parts III and IV. I'm asking this because when I use those demand factors, my equipment seems a little over sized in my opinion. I have been using those factors in my designs, I just wanted to confirm if I had to use them. Thanks in advance, Anthony Cooper


Hi Anthony, thanks for participating in the CQD. Many of the demand factor Code Sections found in Parts III and IV of Article 220 are written as permissive rules, meaning they are not mandatory/required. However, 220.40 only permits demand factors found in Parts III and IV to be applied to service and feeder load calculations. Using demand factors other than those found in Article 220 would not be permitted unless, special permission is granted by the AHJ in accordance with Section 90.4. 

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CHARLIE TROUT: Charles M. Trout, better known as Charlie, was a nationally known NEC® expert and author. He served on several NEC® technical committees and is past chairman of CMP-12. In 2006 Charlie was awarded the prestigious Coggeshall Award for outstanding contributions to the electrical contracting industry, codes and standards development, and technical training. Even though Charlie passed away in October of 2015, his work continues in spirit. NECA continues to maintain this question forum for its many subscribers in memory and recognition of all his significant contributions to making the NEC what it is today.

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