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Thread: Bonding - CID2. Articles 501.30 and 250.96

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    Bonding - CID2. Articles 501.30 and 250.96

    Bonding across hinged doors – Nema 4X Junction boxes and Control Panels, etc, CID2, (24VDC and 120VAC). Its industry practice to do this since the hinge is usually not considered to be a sufficient bond but there doesn't seem to be a NEC article that directly talks to this. I would say 501.30 and 250.96 are sufficient arguments in favor of, but our 'friends' in Construction aren't convinced. Any suggestions?

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    I've always assumed this bond is a UL508 requirement and not NEC, independent of haz area requirements.

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    As I worked in the trade, I always understood it to be required when there was an electrical device mounted in the door. It's obviously a good practice, especiallyHOFFMAN CSD INSTRUCTIONS.pdf in a classified area. I attached a sheet from the Hoffman CSD installation instructions. Just pictures, so there's not much info, but since they show it being bonded, I would say that it is required by the manufacturer and therefore by 110.3 B.

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    Quote Originally Posted by Jim1959 View Post
    As I worked in the trade, I always understood it to be required when there was an electrical device mounted in the door. It's obviously a good practice, especiallyHOFFMAN CSD INSTRUCTIONS.pdf in a classified area. I attached a sheet from the Hoffman CSD installation instructions. Just pictures, so there's not much info, but since they show it being bonded, I would say that it is required by the manufacturer and therefore by 110.3 B.
    good feedback, I will definitely use this as part of my response. Thanks!

  5. #5
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    UL 508a says this.

    66.3.4 An internal bonding conductor shall be provided between a metal cover or a door on which
    electrical components are mounted, and the enclosure or the equipment grounding terminal. The bonding
    conductor shall have an ampacity not less than the largest circuit conductor used to connect the cover or
    door-mounted components.
    Exception: When all electrical components mounted to a metal cover or door are connected to a control
    circuit rated 30V rms or less the bonding conductor is not required.
    HOWEVER, this is in the section that only applies to control panels for industrial machines.

    At one time, UL listed at least some Hoffman enclosures that had continuous SS hinge pins for the doors as being bonded without the need for a conductor being added. I don't know if that is the case anymore.

    Generally if there might be a need for door bonding the enclosure manufacturer will provide studs for that purpose. I don't know that the absence or presence of them is meaningful though.
    Bob

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    Quote Originally Posted by petersonra View Post
    UL 508a says this.



    HOWEVER, this is in the section that only applies to control panels for industrial machines.

    At one time, UL listed at least some Hoffman enclosures that had continuous SS hinge pins for the doors as being bonded without the need for a conductor being added. I don't know if that is the case anymore.

    Generally if there might be a need for door bonding the enclosure manufacturer will provide studs for that purpose. I don't know that the absence or presence of them is meaningful though.
    Ok I will check into - thanks

  7. #7
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    Quote Originally Posted by Jim1959 View Post
    As I worked in the trade, I always understood it to be required when there was an electrical device mounted in the door. It's obviously a good practice, especiallyHOFFMAN CSD INSTRUCTIONS.pdf in a classified area. I attached a sheet from the Hoffman CSD installation instructions. Just pictures, so there's not much info, but since they show it being bonded, I would say that it is required by the manufacturer and therefore by 110.3 B.
    Spoke to Hoffman last night; they will not commit to saying hinges are electrically continuous and refer back to NEC for interpretation - imagine that.
    I'm wondering if a simple resistance test between the two areas (i.e. door and enclosure) would show a significant difference in potential?
    Since you've worked in trades, have you ever done this before?

  8. #8
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    Quote Originally Posted by Dale001289 View Post
    Spoke to Hoffman last night; they will not commit to saying hinges are electrically continuous and refer back to NEC for interpretation - imagine that.
    I'm wondering if a simple resistance test between the two areas (i.e. door and enclosure) would show a significant difference in potential?
    Since you've worked in trades, have you ever done this before?
    I suspect that UL has stopped listing the CH as being a bonding means since Hoffman now puts bonding studs in all their boxes.
    Bob

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