National Electrical Installation Standards

Standards as High as Your Own

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  • February 8, 2019

    For a temporary service can I feed a temp 800 amp panel from (2) existing 400 amp breaker (3) phase 480 volt? The feeders will be sized at 400 amps each feeding a 800 main panel. Is this permitted? Thomas Scimeca
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  • February 7, 2019

    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
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  • February 6, 2019

    When adding an outside disconnect to an existing system and the grounded conductor and frame grounds are all bonded together is it permissible to connect #4 bare copper straight to the ground electrode along with a #4 bare copper to the same ground electrode? Terry Nelson
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  • February 5, 2019

    Using the 2017 code, is it permissible to nipple between two separately fed panels? Thomas Cosgrove
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  • February 4, 2019

    I thought I knew how to wire transformers until a few days ago. There are some guys that say you don't need to bond the transformer to the building grounding electrode system when you aren't using the neutral on the secondary. Say when you have a 480 volt 3 phase 3 wire primary and a 208 volt 3 phase 3 wire secondary to some piece of manufacturing equipment or A/C unit. I have looked through the code book and asked several other electricians and haven't got any real substantial answers or code references. I talked to one person that mentioned the exception in 250.121. I tried to follow it through the code book and I still don't think I understand it. Please help me understand this and find me a code reference so that I can go back to the people asking me these questions and give them some answers. I hope I have explained my issue well enough and my terminology isn't to messed up. I have been reading Code question of the day for a couple of code cycles now and it has been a big help. Thank you for the forum. Vern
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  • February 1, 2019

    Re: CQD answer published Wednesday, January 23, 2019 - Concrete Hole Raceway Regarding the CQD for 1/23/2019 about the concrete wall hole-raceway: My guess is that David's pronoun reference for "doing this a long time" meant that he had been doing electrical work a long time, not using holes in concrete as raceways. =}) Those darn pronouns can be pretty slippery. In any case, this would have to be an installation which an inspector used their 90.4 authority to accept as safe. It certainly could be, as long as an equipment grounding conductor properly bonds the metals on both sides as required in Article 250. The concrete hole could be acceptable as a raceway under 90.4 since it is fully non-combustible. I have indeed received just such an approval (ahead of construction of course) for a case of an old exterior service being refed by a new exterior service - the multi-hundred amp feeder (1200 as I remember it) was run in just this manner. The undisussed concern I would have is if one side of the wall of David's subject is exterior : How is the installation protected from water intrusion and corrosive damage? Scott Cline
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  • January 31, 2019

    After designing and having built over 900 dealerships in 45 years I have never had this field review by a local electrical inspector: that states: "ALL DOMESTIC POWER PLUGS IN THE COMPLETE SHOWROOM AREA AND IN THE LANDSCAPE FURNITURE MUST 18" OFF FLOOR AND NO FLOOR PLUG ARE ALLOWED" Stanley Tkacz
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  • January 30, 2019

    Hi Charlie, is there any rule about stranded vs solid thhn and lug nuts? I constantly find lugs with stranded wire jammed in and was once told they are only for solid and to use a crimp on terminal to connect Christopher Walters
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  • January 29, 2019

    Hello, The term "physical damage is widely used along the NEC. so, I would like to ask if there is any formal definition for this term. Could you please tell me why there is not a formal definition for this term? Is it the AHJ the authority (depending on the country) who has the duty to make a formal interpretation? thank you so much. Diego Medina
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  • January 28, 2019

    Re: CQD answer published January 16, 2019 - Holiday Decorative Lighting Regarding CQD of 01/16/19: I would like to offer a different viewpoint on the topic of holiday lighting installations. I can take an unopened box of holiday lights, toss it onto the roof, leave it there for years, and I will not have created an “electrical installation.” Hanging the lights on the gutter also does not comprise an “electrical installation.” It is only when I run an extension cord or employ some other method to temporarily bring power to the lights that an “electrical installation” will have been created. It is like saying that I need and electrician and a permit in order to get receptacles installed in a new room, but I don’t need one in order to plug a lamp into one of the receptacles. Utilization equipment is not part of the premises wiring system; decorative lights are not electrical installations. Charlie Beck
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  • January 25, 2019

    Thank you for your code insight. I am confused, (my normal state) about 250.66 requirements for grounding electrode conductor size and 250.104 for water pipe and structural steel bonding. A service fed with 5 runs of 500 KCMIL copper would require a 3/0 grounding electrode conductor to the water pipe and building steel. However, 250.104 requires a 350 KCMIL copper the water pipe and building steel. Am I confused, missing something, or merely misinformed. Thanks! Mike
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  • January 24, 2019

    Heighth on riser brackets Mathew Colbert
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  • January 23, 2019

    What type is wire should be used inside the core of a 13” block wall? Dave Guzofsky
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  • January 22, 2019

    I was told today that a drilled concrete hole can be used as a raceway. They drilled through a concrete stand up wall and put a FS box on the outside and a regular 4” square and just run THHN wire through the drilled concrete hole. I’ve been doing this a long time and can’t believe this can be legal. Thanks David
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  • January 21, 2019

    I have noticed a Romex connector to Clamp individual Unjacketed MTW rated wires in a Machine tool Control Panel. Theses conductors will carry 400 volts to and from an Inverter type Motor Drive. Is this a violation of NEC or UL508? Kurt Adlon
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ABOUT CQD: NECA’s Code Question of the Day (CQD) is a leading National Electrical Code® forum for NECA and the industry. The CQD generates a lively dialogue and relative practical and Code-based responses to an ever-increasing and interactive audience.

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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