National Electrical Installation Standards

Standards as High as Your Own

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  • November 12, 2019

    Does garbage disposal need to be gfi protected? Ronald Perez
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  • November 11, 2019

    I have a stepdown transformer 480V-120V. Usually for single phase, 120 Volts is line to neutral, is there any code violation per NEC 250.26 if the connection is 120 Volts line to line, both conductors are ungrounded? Jesus Santos
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  • November 8, 2019

    What is the smallest conductor that can be paralleled? If utility conductors enter a building underground and once entering the building proceed more than 20' to the main disconnect of the building are they in violation of the code?Charles Tucker
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  • November 7, 2019

    Can a breaker box be located on the exterior of a residential property?Donald Tasker
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  • November 6, 2019

    Thanks for the CQOTD. I've been following it for many years, since Brook was still involved. When a conduit runs consists of two types of conduit, is there anything in the NEC that requires me to use the more restrictive fill table? It seems like common sense, but I was just asked if there is a code reference? Thank you,Rich Tomkinson
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  • November 4, 2019

    How many m/c cables can be supported by grid's own grid wire Travis Lawrence
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  • November 1, 2019

    Charlie, I’ve looked at and tried to understand 110.26 and I’m somewhat confused. I believe somewhere it is written door swings on all electrical rooms, small and large, should swing out for safety reasons (Shock, heart, fire). If the electrician is on the floor in front of the door outside help cannot enter. It just seems like common sense to have all doors swing out.Bill Petrovic
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  • October 31, 2019

    About hospital grade receptacles. I do not find the requirement in 517.18(B) that it must be identified with a ‘green dot’. May be in other Section? Carlos Gonzalez
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  • October 30, 2019

    Re: CQD answer published Tuesday, October 22, 2019 - Conductor Size Charlie, Regarding: "The NEC does not require that all conductors in a circuit length be the same size. Sometimes larger conductors are used to deal with voltage drop concerns. Conductors must be protected as stated in 240.4. In your example the 12 AWG conductors are protected below their ampacity and the 14 AWG conductors are protected based on 240.4(D). That is allowed." The problem I have with this wiring is what happens if the service is upgraded (new service panel)? The new electrician will probably use circuit breakers that match the wire size in the panel, not knowing there was a switch to #14 on the second floor (I've done it too many times to remember). A tag would be messy so I think the best 'solution' is to continue with #12 even though it's a pain to work with. Dave
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  • October 29, 2019

    Hi Code Question of the Day and Team Charlie, You all do a fantastic job and provide a great service to the industry! Thank you for linking into the appropriate UL product category guide information in UL Product Spec when explaining the suitability or intended use of UL Certified products in accordance with the NEC. I am writing to let you know that the UL Product Spec database is being retired on November 15, 2019. After that date, that website will be redirected to the UL Product iQ™ database at Going forward, please use the UL Product iQ database. UL Product iQ database is a much more powerful database that includes all of UL’s Certification information, is easy to search by almost any criteria and includes all the search functionality that was included in UL Product Spec. UL Product iQ is free to all users and requires a one time registration. Go to to register today! Thanks and keep up the good work! Best Regards, Tom Lichtenstein Senior Regulatory Engineer UL LLC.
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  • October 28, 2019

    Re: CQD answer published Monday, October 14, 2019 - Working Space In regards to the question below, I would like to offer my observation on this issue of "work space" requirements. In the NEC article covering it, it has a foot note under the table where it states this applies to equipment having "EXPOSED" live parts. The term "EXPOSED" is defined in Art. 100, thus that must be used to determine applicability. It states: Exposed (as applied to live parts). Capable of being inadvertently touched or approached nearer than a safe distance by a person. It is applied to parts that are not suitably guarded, isolated, or insulated. All of the panels now on the market do NOT have EXPOSED live parts when the definition is applied. Even though live parts of terminals can be viewed, they are generally recessed or otherwise arranged (suitably guarded) so that "inadvertent" contact is highly unlikely. Buss bars are covered, screws are recessed, etc. The only way to contact live conductive parts is to "deliberately" do it. This is also true of "safety" type disconnect switches. The hinged cover is interlocked with the handle and the cover can only be opened with the switch in the "OFF" position. When the cover is then opened, the only thing energized is the incoming termination, which is guarded and recessed to avoid "inadvertent" contact. Yes, if the interlock is defeated, then a hazard exists, but this is "deliberate". Here's the Working Space requirement: 110.26 Spaces About Electrical Equipment. Each condition applies to the "Exposed" live parts as defined in Art. 100. If this working space requirement was applied without this caveat, almost every installation would be in violation. Some equipment complies to IEC regulations and quantifies levels of exposure using the Ingress Protection (IP) rating. IP 3, or greater, is generally regarded as "finger safe". IP1 indicates "back of hand" safe, which is also protection against inadvertent contact. Nick Abbatiello
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  • October 25, 2019

    I have done considerable research on this code requirement and it seems clear that you have to size conductors feeding the VFD panel at 1.25 x published max vfd amps. This is a real problem in two scenarios. First, vfd’s often require oversizing as the set carrier frequency is increased above 3kHZ. This has nothing to do with current and everything to do with having a larger bridge to handle additional heat losses at higher carrier frequency. The second scenario is when special configured wide constant hp motors ie rpmac have high output amp requirements but at low vfd output voltage. In this situation the actual output watts reflected back through the rectifier result in much lower drive input amps. In one case, the output amps at 310 vac is 600 amps, but at 460 vac is 400 amps. Following nec 430.122 results in massive cable oversize in the vfd enclosure as well as the cable from the main down stream supply. Very expensive for both the VFD panel builder and end user! In the past, I have seen people just protect against this by limiting current by sizing the incoming vfd enclosure breaker to 1.25 x motor fla (at 460 vac in the case of a 460 vac supply). This seems to make more sense to me! Please let me know if you have any input on this.Thanks! Motorman
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  • October 24, 2019

    I hope this inquiry finds you well. My question is about tap conductors feeding a 35kva 3 phase transformer. 240.21(B)(3) allows a tap conductor for this purpose so long as all condition therein are met. 240.2 generally defines a tap conductor as one that has overcurrent protection above that which is otherwise allowed. Since 450.3 allows overcurrent protection up to 250% of the load where primary and secondary protection are provided, can a #8 Cu THHN, protected by a 100A OCPD, be used for this installation? Can the #8 land directly on the breaker? Would that not meet the definition of a tap? If not, what is the difference in having a #3 land on the breaker only to be spliced to a #8 for the tap?Aeron Braukman
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  • October 23, 2019

    Re: CQD answer published Thursday, October 17, 2019 -Intentional NEC Violation When confronted with a situation such as described in this question in which someone insists that something be done that violates a code or safety consideration, I find it useful to imagine myself in the witness box of a courtroom being confronted by the plaintiff's attorney asking the question "Isn't it correct to say that as a professional electrician, you knew that what you did was a violation of the National Electric Code, yet you did it anyway?" This mental image has given me the fortitude to just say no on more than one occasion. John Kahler
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  • October 22, 2019

    A recent outside audit to a financial institution has requested that locks be installed to lock in the open position all exterior A/C disconnect switches. Is this allowed by code? Robert Cote
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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

CHARLIE TROUT: Charles M. Trout, better known as Charlie, was a nationally recognized NEC® expert and author. He served on several NEC technical committees and is past chairman of CMP-12. In 2006, Charlie was awarded NECA’s prestigious Coggeshall Award for outstanding contributions to the electrical contracting industry, codes and standards development and technical training. NECA continues to provide this public forum in memory and recognition of all his fine contributions that has made 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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