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The National Electrical Code is the bedrock of the electrical construction business.
Do you know all the ins and outs of the Code? NECA and Electrical Contractor magazine are pleased to present their daily online feature, “Code Question of the Day.”
Does NEC code applied to vehicle electrical systems, specially when vehicle has 120VAC outlet?
Why is the size in mm for a 2/0 bare conductor different in the first column of Table 8 in Chapter 9 than the column for overall size? I never noticed before because I usually look for the inches and not metric.
Hey Claudia thanks for your question. It's all about the air spaces, not a metric issue. The values in Col 2 are based on the metric equivalent of the circular mil area of the conductor material. Those are used for sizing the conductors. The overall column values are based on the outside diameters of all the strands, which includes the air spaces between the strands. Those are used for sizing the raceways.
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IMPORTANT NOTICE: All answers are based on the latest edition of the National Electrical Code®, unless the question requests a response based on a specific edition. This correspondence is not a formal interpretation of the NEC®. Any responses expressed to the questions are opinions and do not necessarily represent the official position of NECA, NFPA, or any technical committee. In addition, this correspondence is neither intended, nor should it be relied upon, to provide professional consultation or services.
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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