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Thread: Minimum wire bending radius

  1. #1
    Join Date
    Sep 2004

    Minimum wire bending radius

    I've got a situation where a contractor put in some 500 MCM wire and butchered it pretty badly. Here are the problems, all in about a 12" area:

    1. The wire goes over a sharp edge. The contractor took a side grinder and cut a way a part of the panel cover to keep the edge away from the wire.

    2. The wire is bent at nearly a 90 degree angle. I can't imagine how he did this, unless he stuck it in a vise. The bend is sharper than you'd get if you stuck it in a conduit bender.

    3. The outer casing of the wire is wrinkled up due to the sharp bend, and cut in some places due to the (apparently) large forces used to install it.

    Now, I am trying to find sections of code to cite, other than the "workmanship" clause. Table 312.6B talks about bending space in panelboards, which he has probably ignored. (I will take measurements when I visit the site next week) Conductor damage and wires over sharp edges are pretty easy targets.

    But I was looking for the code reference that tells us we can't bend wires less than a certain diameter. The famously brief index in the NEC code handbook doesn't list anything for "wire bending radius"

    Is minimum wire bending radius addressed in the NEC, or is that a UL issue or a manufacturer's instructions issue?

    Lawrence Lile, P.E.

  2. #2
    Join Date
    Feb 2003

    Re: Minimum wire bending radius

    Look at 300.34 for bending radius. The diameter of 500 is a little over 1 inch. If he took the cable and turn it straight up the radius may not be correct.

  3. #3
    Join Date
    Mar 2003
    Nord'est Wisconsin et Paris France

    Re: Minimum wire bending radius


    if my memory serve me right the bending radius should be 6X of wire dimaiter.

    EX: 500 kcm wire size real size is a shy over a inch dam. so bending radius should be 6 inch or more to prevent damage to conductor insluation coating

    Merci, Marc
    master electrician
    Wisconsin and Paris France

    "Pas de problème, il marche n'est-ce pas?" (No problem, it works doesn't it?)

  4. #4
    Join Date
    May 2003
    Salt Lake City, Utah

    Re: Minimum wire bending radius

    Individual conductor bending radii is only addressed for over 600 volt systems.
    Ryan Jackson, Salt Lake City
    Inspector, Instructor

  5. #5
    Join Date
    Apr 2004
    Mission Viejo, CA

    Re: Minimum wire bending radius

    It is also assumed conductors listed in Table 310.13 will be installed as part of a Chapter 3 wiring method. This includes Articles 312 and 314 which specify the minimum distance relationships of conductors or raceways entering various enclosures; as in 312.6 or 314.28.

    For equipment enclosures Articles 408 and 409 specify wire bending requirements.

    In other words, the requirements are not placed on the 600V conductors themselves, but the wiring methods or equipment.
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  6. #6
    Join Date
    Apr 2003
    Westchester County, New York

    Re: Minimum wire bending radius

    I think Art 312 has plenty to do with the conductors themselves.

    312.6 Deflection of conductors

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