National Electrical Installation Standards

Standards as High as Your Own

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Thursday, February 7, 2019

Question:

In a bathroom, can a 227v switch for lighting be installed in a 2-gang box along with a 120v switch for an exhaust fan? If so is a barrier required?

Richard Cressotti

A

Answer:

Hey Richard thanks for your question. Yes, switches for 277 volt lighting circuits can be in the same enclosure with switches for 120 volt loads. If the voltage between the adjacent switches exceeds 300 volts, identified securely installed barriers are required as stated in 404.8(B).

So, depending on the systems supplying the two different circuits the voltages can be additive, subtractive or theoretically neither, to each other. Either measure the difference between the two circuits and show the AHJ it does not exceed 300 volts or use barriers that are readily available. If you have the interest and time, using safe work practices, check the actual voltages, with different circuits and systems if possible, and send that information in to us. It might be an opportunity to help improve the NEC wording in future editions.

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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.

NECA STANDARDS: NECA publishes the National Electrical Installation Standards™ (NEIS™), a series of ANSI-approved performance and quality standards for electrical construction. Visit NECA-NEIS.org for more information. NEISÔ can be purchased in three formats: as paper books, on CD, or as electronic downloads.

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