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Friday, April 30, 2021

Question:

Hello Code Question of the Day.

Thanks for the great information. What is the minimum conduit size for an 80-ampere, 3-phase circuit circuit?

Charles Smith

A

Answer:

Hi Charles,

The response to your questions is based on the information provided. There is information missing such as the type of conduit or tubing,  ambient temperature  and location where the conduit is installed, type of conductor insulation, etc. Based on the Tables of the NEC (Specifically Table 310.16 and Table 1, Chapter 9). Table 310.16 indicates a 3 AWG copper conductor (Type TW) is good for 85 amperes with no ampacity adjustments or correction factors or applied. So (3) 3 AWG conductors would require a minimum 1/2 inch looking at Table C9. This response does not address any associated equipment grounding conductor that may also be required in the conduit.

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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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IMPORTANT NOTICE: Unless the question requests a response based on a specific edition, all answers are based on the latest edition of NFPA 70® National Electrical Code®.

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