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Thread: SQ-D panel bonding screw

  1. #1
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    SQ-D panel bonding screw

    There's some model of SQ-D QOB panels (all installed as service equipement) we've been swapping out dozens of for something else and I've noticed on the tearout of the old panels that the panel bonding screw doesn't really bond to the can itself, it screws into the rails the guts are mounted on, then relies on the guts to be bolted up firmly to actually make the bond.

    The original EC apparently removed the guts to punch/mount the can then wasn't so careful about bolting the guts back in and left quite a few rather loose. There was quite a few of these where I noticed visible arc burn between the can and mounting rails.

    Shouldn't a bonding screw actually be required to bond, particularly when you know the EC is very likely to take the guts out to punch/mount the thing?

  2. #2
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    Why would the EC take the guts out to punch/mount the can? I don't get it.

    In any event, the bond screw it a thread forming tri-lobed screw. It makes a good bond. Roll a new one through your fingers, and you'll feel the lumps of the three lobes. It is not completely round. You can perceive that if you visually examine the bond screw, end-on.

  3. #3
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    Quote Originally Posted by mdshunk
    Why would the EC take the guts out to punch/mount the can? I don't get it.
    I don't know. The old ones are quite heavy. The new stuff is cheap/light residential junk (its what the customer engineers spec'd, not our decision)

    In any event, the bond screw it a thread forming tri-lobed screw. It makes a good bond. Roll a new one through your fingers, and you'll feel the lumps of the three lobes. It is not completely round. You can perceive that if you visually examine the bond screw, end-on.
    On these panels, its not that kind of screw. Its an ordinary machine screw into the guts mounting rails -- it never penetrates the can, only the mount rails holding the guts together. IOW - if you remove the 4 nuts holding the guts in and remove the guts, this bond screw comes along for the ride.

    I'll see if I can get a pic of this lashup. There's another two sites with the SQ-D panels we're swapping out tomorrow.
    Last edited by tonyi; 04-15-07 at 09:33 AM.

  4. #4
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    Commercial panelboards frequently come in two or three boxes, with the guts left in the trailer until they are needed.

    I've seen plenty of round bonding screws. :confused:

    If the installer didn't snug down the guts, then why do you think they would snug down a bonding screw instead? They all need to be tight.

  5. #5
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    Quote Originally Posted by georgestolz
    Commercial panelboards frequently come in two or three boxes, with the guts left in the trailer until they are needed.
    Yes, but I have never seen the bonding jumper depend on the mounting hardware.

  6. #6
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    Most have the original labels w/model numbers intact. I'll scribble down some of that stuff in the AM then we can be more specific about what I'm talking about.

    Its odd, I've not seen anything like this. Course...maybe the original EC threw away SQ-D's bonding scheme and just used their own bogus lashup too ;->

    The Army corps of engineers never had the sites inspected originally ;->

  7. #7
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    Most panelboards (as opposed to load centers) have a removable interior. The interior is usually mounted to the box with four leveling screws/bolts rather than directly to the back of the box. On the current generation of NQOD (versus the older NQO/NQOB) panelboards the neutral to box jumper is a strap and not a simple screw.
    Just because you can, doesn't mean you should.

  8. #8
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    Delmarva, USA
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    Arrow

    Quote Originally Posted by mdshunk
    Why would the EC take the guts out to punch/mount the can? I don't get it.....
    When dealing with panelboards (as opposed to load centers), the guts are packaged and shipped separately. When roughing in your building, the empty can is mounted and conduits are installed. We usually pull all the wiring in the conduits before installing the guts, to minimize on damage or injury during this process.

  9. #9
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    Quote Originally Posted by kbsparky
    When dealing with panelboards (as opposed to load centers), the guts are packaged and shipped separately. .
    Yes, that was my point. The guts are already out of a commercial-style can. If they had to remove them, I'm thinking a resi, plug-on style. That's where my confusion came in.

  10. #10
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    I have removed the guts from even a residential panel on more than one occasion; pulling feeders in conduit comes to mind.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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