Ecmweb 14816 Nec Multiwire Branch Circuits 0
Ecmweb 14816 Nec Multiwire Branch Circuits 0
Ecmweb 14816 Nec Multiwire Branch Circuits 0
Ecmweb 14816 Nec Multiwire Branch Circuits 0
Ecmweb 14816 Nec Multiwire Branch Circuits 0

Multiwire Branch Circuit Rules on Construction Sites

June 28, 2017
Confusion may abound when it comes to figuring out the rules for multiwire branch circuits on construction sites.

Are you ready to chase your tail and keep going around and around the way a dog or cat does? That may happen when it comes to figuring out the rules for multiwire branch circuits on construction sites. The last sentence of Sec. 590.4(D)(1) seems pretty straightforward. It states, “Receptacles on construction sites shall not be placed on any branch circuit that supplies temporary lighting.” Some would say that this also includes multiwire branch circuits because the Art. 100 definition defines a multiwire branch circuit as a single circuit. Others, however, would point to Sec. 210.4(A), which clearly states a multiwire branch circuit can be considered multiple circuits as well. So where does this leave us for applying the rules in Sec. 590.4(D)(1)? Is a multiwire branch circuit a single circuit or is it multiple circuits?

The last sentence in the following OSHA rules seems to imply that using a multiwire branch circuit would be permitted if arranged correctly. “1926.405(a)(2)(ii)(C): Receptacles shall be of the grounding type. Unless installed in a complete metallic raceway, each branch circuit shall contain a separate equipment grounding conductor, and all receptacles shall be electrically connected to the grounding conductor. Receptacles for uses other than temporary lighting shall not be installed on branch circuits which supply temporary lighting. Receptacles shall not be connected to the same ungrounded conductor of multiwire circuits which supply temporary lighting.”

What about when a fault occurs? Breakers with independent-trip poles are available. Single-pole breakers with handle ties are permitted by Sec. 240.15(B)(1). Here’s something else to consider: Using a common trip breaker on a multiwire branch circuit would “essentially” be the same as having the receptacles on the same phase as the lights since both would be shut off in the event of a fault. However, some would say using that type of breaker is not prohibited by the NEC or even the OSHA rules, so long as the receptacles and lights were not on the same phase. Yet others will take the position that Sec. 590.4(D)(1) states: “any branch circuit”...including multiwire!

I think this rule (as currently written) could easily have “a line drawn in the sand” with strong arguments on both sides due to the present wording. It would probably be a good idea to discuss this issue with your AHJ to come up with a circuit arrangement that works best for all parties involved.

About the Author

Russ LeBlanc | Owner

Russ started in the electrical trade as an apprentice in 1985. He worked his way up to become a Journeyman Electrician and then eventually became a Master Electrician and Licensed Construction Supervisor. In 1999 Russ become an Electrical Instructor for The Peterson School of Engineering in Massachusetts where he developed his passion for teaching, and quickly became Department Head of Electrical Instruction. Russ has taught thousands of apprentices, electricians, engineers, inspectors, and other electrical professionals during his career as an instructor. He continues to provide electrical professionals with Electrical Code seminars, Arc-Flash Awareness training seminars and educational material through his LeBlanc Consulting Services in North Reading, MA whose specialty is educating electricians. He has been an active member of the NFPA Electrical Section and has authored hundreds of National Electrical Code proposals and comments which have become Code rules to improve the safety for the electrical industry. Russ is also an IAEI certified Electrical Inspector.

Please visit www.russleblanc.net for more information.

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