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Thread: Load Center Wiring Questions

  1. #1
    I&C Engineer (mostly WWTP) Lakee911's Avatar
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    Default Load Center Wiring Questions

    Am I allowed to double lug (a circuit breaker) for a hardwired secondary surge arrestor?

    Considering the fact that the main disconnect is a suitable overcurrent protection device, I could connect the device to the bus bar lugs. The wire size is too small, so how could I fit a #12 wire into a lug designed for something like #1 wire?

    Are wire connectors allowed in a panel? I'm replacing a panel and would like to know how to lengthen existing wires if the connectors are not allowed.

    Panel is mounted against the wall and the ceiling is low (6.5 or 7ft). Can I bundle the cables (with wire wraps) coming in overhead through one large 2in. knockout and through one cable clamp, or must I bring them in seperately, in conduit? The distance to the ceiling will only be a few inches.

    If I mount a 3/4" piece of plywood directly on the masonary block wall with powder actuated fasteners, will 3/4" long fasteners in the plywood alone be adequete to carry the weight of the panel?

    Thanks,
    Jason

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    Retired Defense Industry Engineer jadnashua's Avatar
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    The supressor I have on my panel specifically states in the installation instructions that it must be on its own breakers (either one 220 or two 110 on separate legs).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Electrician Chris75's Avatar
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    What did the instructions that came with the surge protection say?

    and no, you cannot have two wires under one screw...

  4. #4
    I&C Engineer (mostly WWTP) Lakee911's Avatar
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    It didn't say anything about dedicated breakers on the instructions.

    I thought I couldn't have two wires under one screw but an electrician told me otherwise (not that it makes it right). He's a friend, so I didn't want to ask for a code reference.

    Jason

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    In the Trades Bob NH's Avatar
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    All of my new breakers have connections that are designed for one or TWO wires. You can tell if the connection has a small plate under the screw with a place for a wire on each side of the screw.

    If your surge protector has wires coming from it and no terminals for mating to the lugs of the panel, then it is made to be wired into a circuit. I would just follow the instructions.

    Wire nut connections in the service panel are PERMITTED if there is room, and there is in any modern service panel.

  6. #6

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    no, you cannot have two wires under one screw

    Sure you can...if the breaker is designed/rated for two conductors ie. SquareD QO style.

  7. #7
    I&C Engineer (mostly WWTP) Lakee911's Avatar
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    Ok. Well, that's the panel in question.


    What do you all think of the other questions?

    Thanks

  8. #8
    Plumber Cass's Avatar
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    What you can't / shouldn't do is put 2 different size wires on the same breaker like taking a #12 and #14 wire and putting it on a 15A breaker. I have found a few situations like this and the #14 becomes loose because of uneven applied torque due to the wire size difference.

  9. #9
    Electrician Chris75's Avatar
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    Quote Originally Posted by Alectrician View Post
    Sure you can...if the breaker is designed/rated for two conductors ie. SquareD QO style.
    I knew it had to be listed, just did not know sq. D had allowed it.. thanks...

  10. #10

    Default Re: Panel Questions.

    [QUOTE=Lakee911;119757]



    Can I bundle the cables (with wire wraps) coming in overhead through one large 2in. knockout and through one cable clamp, or must I bring them in seperately, in conduit? The distance to the ceiling will only be a few inches.


    No you can only have 3 cables in each knockout. Table 310-16. Unless you de-rate them.



    If I mount a 3/4" piece of plywood directly on the masonary block wall with powder actuated fasteners, will 3/4" long fasteners in the plywood alone be adequete to carry the weight of the panel?

    I dont like using PAFs I have seen too many services hung up by the riser because the pins come out. I would use tapcons they have never let me down.

  11. #11
    I&C Engineer (mostly WWTP) Lakee911's Avatar
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    Well, you're a few days late, since I already used the pins! I put in seven 1-1/2" pins. I don't think it's going anywhere. I'll keep an eye on it. I'll add tapcons if they start to move.

    Jason

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    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    [quote=lampman42;122519]
    Quote Originally Posted by Lakee911 View Post
    Can I bundle the cables (with wire wraps) coming in overhead through one large 2in. knockout and through one cable clamp, or must I bring them in seperately, in conduit? The distance to the ceiling will only be a few inches.

    No you can only have 3 cables in each knockout. Table 310-16. Unless you de-rate them.
    I would use a short piece of 2" RNC. Then Chapter 9 applies, not 310-16 (300.17 FPN, 352.22). The computation is not simple, depends on the number and size of conductors and types of insulation, and does not apply anyway to "sections of conduit or tubing used to protect exposed wiring from physical damage." (Note 2 to Table 1.) Every installation I've seen like this uses a couple feet or so of 2" of RNC filled until no more cables will fit. I use a "fill loosely" rule of thumb. I would also run 3 pieces from the panel up to wherever you're going (attic?) to allow for future expansion.

    I'd like to hear a real Code junkie's take on this. Maybe there's some wisdom to be found in Mike Holt's forum.
    Last edited by Mikey; 02-08-2008 at 04:27 AM. Reason: various

  13. #13
    Electrician Chris75's Avatar
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    Quote Originally Posted by Lakee911 View Post



    Can I bundle the cables (with wire wraps) coming in overhead through one large 2in. knockout and through one cable clamp,
    No, each cable shall be secured to the cabinet. Some connectors will allow two cables in each connector...


    Quote Originally Posted by Lakee911 View Post
    or must I bring them in seperately, in conduit? The distance to the ceiling will only be a few inches.

    ONLY IF you meet the following... (which you probably don't... I have yet to see a code compliant installation of this section)

    Cables with entirely nonmetallic sheaths shall be permitted to enter the top of a surface-mounted enclosure through one or more non flexible raceway not less than 18 in. or more than 10' in length provided all of the following are met:

    (a) Each cable is fastened within 12" of the outer end of the raceway
    (b) The raceway extends directly above the enclosure and does not penetrate a structural ceiling.
    (c) A fitting is provided on each end of the raceway
    (d) The raceway is plugged or sealed
    (e) The cable sheath is continuous through the raceway.
    (f) The raceway is fastened at its outer end
    (g) you meet the allowable cable fill
    Last edited by Chris75; 02-08-2008 at 03:15 PM.

  14. #14
    Electrician Chris75's Avatar
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    [QUOTE=Mikey;122583]
    Quote Originally Posted by lampman42 View Post
    I would use a short piece of 2" RNC. Then Chapter 9 applies, not 310-16 (300.17 FPN, 352.22). The computation is not simple, depends on the number and size of conductors and types of insulation, and does not apply anyway to "sections of conduit or tubing used to protect exposed wiring from physical damage." (Note 2 to Table 1.) Every installation I've seen like this uses a couple feet or so of 2" of RNC filled until no more cables will fit. I use a "fill loosely" rule of thumb. I would also run 3 pieces from the panel up to wherever you're going (attic?) to allow for future expansion.

    I'd like to hear a real Code junkie's take on this. Maybe there's some wisdom to be found in Mike Holt's forum.
    Check out my post... its very hard to be able to just slap a piece of raceway up and use it for homeruns...

  15. #15
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    May be very hard, but very common, and have apparently passed inspection. Can you give me the chapter & verse on that citation? There must be a loophole...

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