National Electrical Installation Standards

Standards as High as Your Own

Tuesday, September 4, 2018


There are 2 sections I'd like to be clarified 1. Load calculations per 220.40 2. Grounding per 250 service grounding. - 1

Bob Gregg



Hey Bob thanks for your questions, we will answer them in general, but separately If you have a specific detail you need an answer for regarding either of the questions please send it in.

All the loads supplied by a feeder or service conductor are added together based on branch circuits they supply (Using Part II of Article 220) as stated in 220.40. This is considered the total connected load. Demand factors in Parts III, IV< and V of Article 220 are applied because it is often unlikely that everything will be operating at full rating at the same time. This is considered the calculated load. For example lighting loads have varying demand factors based on occupancy types as shown in Table 220.42. There are many variations and the examples in Informative Annex D can help in understanding how the calculations are done.

See tomorrow's CQD for the second question.

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ABOUT CHARLIE: 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. Charlie was also a member of NECA’s Academy of Electrical Contracting. Charlie’s experienced team of industry experts keep the CQD dialogue and discussions active and informative in the spirit of the man himself, as he wanted.

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