National Electrical Installation Standards

Standards as High as Your Own

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  • July 18, 2019

    Re: CQD answer published Wednesday, July 10, 2019 -NM Cable Adjustment Factor Hi Charlie 2.0, Regarding the answer provided to the question for Tuesday 7/9/2019, just wanted to point out the 80% adjustment factor mentioned in the answer is applied to the ampacity allowed for the maximum conductor temperature. For NM-B Cable, the conductor insulation is rated 90C therefore the ampacity adjustment is applied to the 90C ampacity. In this situation (12/4 or 12/2/2 NM-B), that would give an allowable ampacity of 0.8 x 30 Amps = 24 Amps. Since this calculated result is higher than the 60C ampacity, we must use the lowest of the two values which is the 60C ampacity. The net result is that a 4 conductor 12 AWG NM-B Cable (whether it is one circuit or two circuit) has an ampacity of 20 Amps – just like the 12/2 and 12/3 NM-B Cables. If multiple cables are bundled together, further ampacity adjustment may be required.Dave Watson, Southwire
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  • July 17, 2019

    Circuit Question - I have bathroom between to rooms that share 4 inch stud wall and I know that bath will have its own 20 amp dedicated circuits but rooms around bath can have 15 amp circuit or it needs to be 20 amp? my concern is that if I use 15 amp circuit for room around bath then 14/2 NM cable will be passing through walls which is shared by bathroom and rooms around it. Al Dhan
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  • July 16, 2019

    Re: CQD answer published Tuesday, July 9, 2019 -Broken Light Pole 1) My suggestion is to check safety codes of the city and state. I would strongly suggest she hit the utility where it hurts. In the pocketbook. The lady asking the question should question the city about whether the utility has adjusted the billing to the city since they are not providing the services they are billing for. Dave Goetz 2) Mike (assuming you are still there), and the rest of the Charlie Trout team, thanks for your great service to the electrical industry. This is in response to Monday, July 8, 2019 answer. Yep, I am a utility guy. It is interesting to note that very large number of REMCs and municipal utilities are not covered by the National Electrical Safety Code nor are they controlled by the public service commission in their state. Most will follow the NESC but there may be no laws that require them to follow it. In addition, the electric utilities that are required to follow the NESC, their state may not adopt the current edition (The State of Indiana’s current adopted NESC is the 2002 edition). I have a hard time believing that any electric utility would be as unresponsive and callused as this one seems to be especially where public safety is concerned. I am not aware of any portion of the NESC that permits bare exposed live conductors to just be covered with a traffic cone and call it good. In my opinion, contact in order the outage/trouble department of the electric utility the underground line department the safety department call 911 contact the public service commission in writing to file a formal complaint Calling 911 first is like attempting to use a sledge hammer to drive a tack. However, it may take a sledge hammer to get their attention. The first call should get their attention if the call is to the correct location in the company.Take Care, Charlie Eldridge
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  • July 15, 2019

    Hi Charlie! I appreciate everything you are doing and enjoy the daily code questions. What types of conductors and circuits does 240.4(B) apply to? Service and panel feeders, sub panel feeders, motor circuits, what types of branch circuits? Thank you for your time!Respectfully, Timothy J. Rein
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  • July 12, 2019

    Can an outdoor 4x breaker panel be used indoorsTroy Clendenning
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  • July 11, 2019

    I need a neutral to make 277v LED lights work. The city park poles have 3 phase 480v. I’m wondering if I can run a ground rod into the j boxes to ground the poles and drop a phase to use it as a neutral by hooking it up the the previous ground wires that go to the point of service. Is this allowed by the NEC?Matthew Greb
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  • July 10, 2019

    Hi, I have an underground tank with a pump inside the tank installed. It was found that the tank was not adequately isolated from other metallic structures in the area. Two wires from the pump were bonded to the tank. If a Solid State Decoupler is installed on the ground level to route grounding wire thru from the pump inside the tank to the earth, is it code compliant? Or is it a code violence? I assume basically decoupler is a capacitor. Thank youHyunmin Oh
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  • July 9, 2019

    I with others appreciate being able to get the brain working every morning with thought provoking questions. When using 12/2/2NM cable in a residence is derating still required? It would be considered a cable but 2 individual circuits. I can agree with temperature limitations as with any NM cable in an attic but the question has been raised that there are more than 3 current carrying conductors therefore derating is required. Hot topic for awhile here in the local area of Indiana (still on 2008 NEC requirements) Thanks for any feedback!James Jett
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  • July 8, 2019

    Hi I am curious regarding the safety of a broken light pole near my home. 3 months ago, a light pole was knocked over by a snowplow. The light pole is not owned by the city I live in but rather by a local power company, and the city pays them a monthly rent for all the lights in the town. After the fiberglass pole was knocked over, there was approximately 3 feet of the pole left coming out of the ground, with of course a hole in the top that they covered with an orange cone. There is also a hole in the pole about 10 inches off the ground. After questioning the local power company about when the new one is coming, as it has been several months, I randomly said something like, well it isn’t live right, no one can get hurt by it. They informed me that yet it was live, as they do not have a shut off at each pole, so would have to turn off all the lights on our entire and not just the one. After doing some more looking with more experience people, they pulled the wires out from the hole on the side, the wires had nothing on the end, there was a ground wire, and another wire that was “live” not sure what the voltage was, but they had checked that and said to me “enough to kill a kid easily” as of course my kids safety is what I am worried about, not so much an adult…… The guys were there looking at this with me (not from the power company remind you) did put electrical tape on the end of the wire. I have contacted the power company numerous times and I get no where. Another neighbor put it on facebook, their response was that they covered the hole (not the one on top with the cone over it but the one on the side right up from ground) and they covered it with what looks like black duct tape. I am assuming this cannot be to code – however I am having a hard time finding what codes are in relation to power/utility companies etc.Thank you, Kara Trom
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  • July 5, 2019

    Can you mix control wires with 480 volt motor load wires in the same conduit or trouffe Gene Capalbo
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  • July 4, 2019

    My question is in regard to the rating of branch circuit(s) for dwelling unit garages. I have a 2 vehicle bay garage and a receptacle is installed 3 feet above the floor in each vehicle bay. I want to install an individual branch circuit for a 2.7 amp overhead garage door opener. Can I use a 15 amp branch circuit to serve the garage door opener? If your answer is no, (it too must also be on a 20 amp circuit), what do I do if I want to install a receptacle for my central vacuum system in the garage and the installation instructions require a 15 amp individual circuit?Thanks, Don
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  • July 3, 2019

    Is it a code violation If we have 4 square boxes being used as junction boxes above a grid ceiling where the tiles are locked into place with clips? if so what code? thanksRobby Robertson
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  • July 2, 2019

    Can you leave 4/0 cable conductors as "pig tails" hooked to the load side of a 3 phase 480v transformer? Is it against code to leave them hooked up and hanging inside the transformer after line power has been restored?Erik Briggs
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  • July 1, 2019

    In a structure, separate services are not permitted to serve multiple units. The subject has come up again and I need to back it up with the proper code. My great mentor recently passed or I would have asked him. What code would property state this? 230.3 or 230.6 would be my answer but would like your opinion...please Scott Ammon
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  • June 28, 2019

    250 Amp Service Feed with 350 ALU ground sizeCharles Gaddy
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ABOUT CQD: The Code Question of the Day (CQD) is NECA and ELECTRICAL CONTRACTOR Magazine’s flagship National Electrical Code (NEC®) public forum for the industry, sponsored by EATON. The daily distribution of Q&A generates a lively dialogue and shares relative Code-based practical responses.

SUBMIT YOUR CODE QUESTION: Click here to submit a question to for inclusion in an upcoming edition of the Code Question of the Day, or email codequestion@necanet.org

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®.

This correspondence is not a formal interpretation of the NEC® and any responses expressed to the questions are opinions and do not necessarily represent the official position of NECA, NFPA, the NEC Correlating Committee any Code-making panel or other electrical technical committee. In addition, this correspondence is neither intended, nor should it be relied upon, to provide professional consultation or services. 

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