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Discussion Forum

bonding screws in Breaker panels

wedalucas | Posted in General Discussion on August 9, 2008 07:07am

General contractor, amateur electrician.  What are the guidelines for using the bonding screw in breaker panels and/or sub-panels?  Thanks.

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Replies

  1. FastEddie | Aug 09, 2008 07:08pm | #1

    Rightie tightie, lefty loosie.

    "Put your creed in your deed."   Emerson

    "When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it."  T. Roosevelt

  2. Piffin | Aug 09, 2008 07:17pm | #2

    I am not an electrician anymore than you are. Maybe i don't understand the Q any better than Eddie.

    But I think what you mean is that in the primary panel you bond the box, but in subpanels the box is not bonded.

    one of the electricians will be along to corrtect all of us soon.

     

     

    Welcome to the
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    Knowledge FHB Campus at Breaktime.
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  3. User avater
    BillHartmann | Aug 09, 2008 07:38pm | #3

    At the service entrance you have the main disconnect. At the service entrance the neutral is bonded to the ground electrode system and equipement grounding conductors.

    This might all be done at the main disconnect and/or in the meter box.

    In many installations the "main" panel is the main disconnect. But insome there is a disconnect only or a disconnect and small panel, usually at or near the meter, and the "main panel" inside is realy a sub-panel.

    Any panels downstream of the main disconnect and in the same structure is a sub-panel and the neutral bus must be isolated from the ground bus.

    In a detached structure under the 2008 NEC a sub-panel needs a 4 wire connection (2 hots, neutral, ground) for a 240/120 single phase service and the neutral is unbonded.

    Under older codes a 3 wire service (2 hots, and neutral) was allowed under some circumstances and in that case the neutral is bonded.

    .
    .
    A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
    1. wedalucas | Aug 09, 2008 08:26pm | #4

      Thanks Bill.

    2. Bpawb | Aug 09, 2008 09:01pm | #5

      "Any panels downstream of the main disconnect and in the same structure is a sub-panel and the neutral bus must be isolated from the ground bus."

       

      What happens if the neutral  and the ground bus  are bonded in a situation as described above?

       

      ...thanks, paul...

      1. User avater
        BillHartmann | Aug 09, 2008 09:10pm | #6

        The whole concept of the equipment grounding conductor (that is what connects to the ground pin on a receptacle) along with the bonding internal metalic water pipes, gas pipes, and hvac ductwork (the later usually done via the grounds on appliaces) is that any exposed metal in the house is at the same potential.The only way that you can guarantee that they are the same potential is have a set of conductors that normally don't carry current. If they carry current then you will have a voltage drop different parts will be at different voltage levels.If the neutral was bonded at the sub-panel then you would have current flowing through the equipment grounding conductor back to the main panel..
        .
        A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

        1. Bpawb | Aug 09, 2008 09:26pm | #7

          If I'm not mistaken, I think my Neutral & Ground buses are bonded at both the service entrance/main disconnect.... and also at the downstream 40 space panel....Ifso i will get back w/ you tomorrow for more advice.

           

          thanks...paul...

        2. Bpawb | Aug 11, 2008 10:24pm | #8

              Took a extra day to get back w/ you,... anyhow...I think they are bonded at both locations.....here are pictures...

             The green screw to the left of the neutral lug in the breaker panel (1st picture) is screwed down snug. 

           

                        I assume this means it is bonded?

           

             And you can see in the second picture that the neutral and ground are bonded.

           

            Is it a danger factor w/ them bonded at both locations?

           

          thanks...paul...

          1. marv | Aug 11, 2008 11:47pm | #9

            I don't think that screw is bonding the panel.  Please take a picture of the whole panel with a little higher resolution.You get out of life what you put into it......minus taxes.

            Marv

          2. arcflash | Aug 12, 2008 02:49am | #10

            Bonding is usually accomplished via a metal bar between the grounded conductor bus (neutral) and grounding conductor bus (ground). The easiest way to tell is if you have green and white wires mixed together on the bus bars in the panel. There will be a bonding jumper (basically a flat metal bar) between the two bus bars. This is done one time at the first means of service disconnect. Bill pretty much nailed it as far as the reasoning for this. In a fault, your neutral ahead of the sub panel would be carrying twice the load back to the main on a double bonded system, that has the potential to over-heat the wire, resulting in a fire hazard.

          3. DanH | Aug 12, 2008 10:16pm | #21

            Isn't all this talk of bondage on a bus in violation of the new rules?
            It is an ironic habit of human beings to run faster when we have lost our way. --Rollo May

          4. arcflash | Aug 13, 2008 03:57am | #24

            That is a good question, but no. The NEC '08 has not been adopted yet, at least where I live.

            As far as I know, bonding the neutral and ground, and the ground to the panel box is still Code.

          5. User avater
            BillHartmann | Aug 13, 2008 06:42am | #25

            HintAll messages that are posted are always 100% directed to the subject at hand.I don't think that the NEC has any rules on the subject that Dan asked about..
            .
            A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

          6. rasconc | Aug 13, 2008 06:55am | #26

            It's code.For those who have fought for it Freedom has a flavor the protected will never know.

          7. User avater
            BillHartmann | Aug 13, 2008 06:57am | #27

            I wonder if AF will ever figure out the BT code?.
            .
            A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

          8. rasconc | Aug 13, 2008 07:00am | #28

            I thought he was an expert in all fields.  Maybe skilled trade worker does not cover that area (:-).  Dog bone for finally filling out profile.

             Minor related hijack, that issue for the d/c and t/s.  I know sub is supposed to be four wire but a dedicated 240v one should not have to have a neutral should it?  Put label beside ground bar (green screw through to box) 240 only, no neutral and label on trim, 240 only.  This is recycle of old dryer circuit. 

            For those who have fought for it Freedom has a flavor the protected will never know.

            Edited 8/13/2008 12:01 am ET by rasconc

            Edited 8/13/2008 12:07 am ET by rasconc

          9. gfretwell | Aug 13, 2008 08:09am | #29

            That is true, If you don't serve any 120v loads you don't need to bring a neutral into that enclosure. The only place that really needs to have the neutral is in the service disconnect enclosure.

          10. rasconc | Aug 13, 2008 05:22pm | #32

            Thanks to you and Bill.  That is what I thought, knew most everything is supposed to be 4 wire but the items it is for are shop equipment that is two hots and egc.  Went ahead and got a 8/16 box so I could add another 15a dp if I decided to convert the band saw also. 

            Felt that since there would be the other spaces in there putting the caution might keep someone not smart enough to know better from adding a single pole and using the ground buss for neutral.

             For those who have fought for it Freedom has a flavor the protected will never know.

          11. User avater
            BillHartmann | Aug 13, 2008 04:28pm | #31

            I don't know of anything that would require a neutral at the sub-panel. OTOH, I have never had the need to try and feed something like this in the code.
            .
            .
            A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

          12. arcflash | Aug 14, 2008 01:07am | #34

            I was told today by a journyman electrician that an anti-oxidizing agent is required by code on aluminum wire. Code or not, you had better use it.

            And if you did what I do for ten hours a day, seven days a week, you would probably understand a little bit about the trades, too.  

            I guess I dont spend enough time on the computer to understand how these forums work.

          13. User avater
            BillHartmann | Aug 14, 2008 01:32am | #35

            He still doesn't get it.This is what Dan wrote."Isn't all this talk of bondage on a bus in violation of the new rules?"Note - it does not have anything to do with electricity. Nor with the "trades". But it might be related to the worlds oldest profession..
            .
            A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

          14. gfretwell | Aug 14, 2008 08:24am | #36

            You may have a local code that requires antioxidant but it is not in the NEC.
            The only cite I have ever heard is 110.3(B), manufacturer's instructions but the devil is in the details. Some lug manufacturers "recommend" the paste but it is not "required", a significant legal distinction in the NEC style manual. I don't know of any aluminum wire manufacturer who says you should use it. In fact Alcan's reps tend to say it is useless.

          15. User avater
            BillHartmann | Aug 12, 2008 02:54am | #11

            The problem is more than just bonding. When the neutral is not bonded to the grounds" that means ALL neutrals are isolated from all grounds.Neutrals include the incoming neutral feeder and the neutrals to each load.Grounds include the incoming equipment grounding conductor, if any, the equipment grounding conductor to each load, ground electrode conductors (to ground rods, water main, etc) if any, and the metal panel case.Now I can't tell from that picture. Some panels with dual busses like that one buss is permanently grounded and the other connects to the first with a strap that grounds the other one. With the strap removed the 2nd buss is a floating neutral bus.I can't see enough see where the incomeing ground wire attaches. But it looks like left bus has both neutrals and grounds on it.Also it looks like some of the ground wires are just twisted together (upper left) instead of using continuing each individually to the bus.
            .
            .
            A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

          16. Bpawb | Aug 12, 2008 04:41am | #13

                Hi, All the grounds are on a separate bus of their on to the far left ( in 1st  picture )...........Note: the ground bus is mounted directly on the metal panel.

               There are 2 neutral buses on either side of the breakers ...they are connected  to each other with what looks like  a piece of #4 copper ,   called a  NTL strap.....

               .......Note: you can see ( in 2nd picture ) the neutral buses are isolated from the metal panel via the black plastic plate.

               Now,   the way i understand it is; when you tighten the green screw (the screw is in 2nd picture just to the left of the neutral lug) you are connecting / bonding both neutral buses to the metal panel...and thus connecting/bonding both ground and neutral buses.

             

              I hope this is clearer than mud....if not let me know and I will try explain in different wording

            thanks...paul...

             

              

          17. User avater
            BillHartmann | Aug 12, 2008 06:58am | #14

            From what you say it appears that removing the green screw is all that you need to do.
            .
            .
            A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

          18. Bpawb | Aug 12, 2008 04:59pm | #15

            Thanks, Bill

          19. Bpawb | Aug 12, 2008 07:50pm | #17

            Another question;      If I disconnect the bare alum. ground wire at the Main Disconnect-- (the ground wire that connects main disconnect with the breaker panel)--   

                 --And then connect a ohm meter between the Ground buss and the Neutral Busses inside the breaker panel--  --Should I get a beep???

              Because I did    and (with my limited knowledge)I was thinking I should not have gotten a audible beep between the two?

             

            thanks...paul...

             

          20. User avater
            BillHartmann | Aug 12, 2008 07:57pm | #18

            "--And then connect a ohm meter between the Ground buss and the Neutral Busses inside the breaker panel-- --Should I get a beep???"No..
            .
            A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

          21. Bpawb | Aug 12, 2008 08:04pm | #19

            Any suggestions on where to start trouble shooting?

          22. Bpawb | Aug 12, 2008 08:06pm | #20

            Also ,  when I check voltage between service entrance wire at the breaker panel  and  the ground ,  I get a reading of 120v.

          23. arcflash | Aug 13, 2008 03:55am | #23

            You should get a reading of 120V. And if you check between both hot feeds, you will get 240V.

            When you said that you need to troubleshoot, exactly what are you looking for?

          24. Bpawb | Aug 13, 2008 02:53pm | #30

                Just trying to find out a sure-fired way to make sure i am not double bonded.        Or that my neutral's and ground's are isolated except at the main disconnect.

             

            thanks...paul...

          25. gfretwell | Aug 13, 2008 10:47pm | #33

            If you really want to be sure you have eliminated all neutral to ground paths you need to unplug everything. I have a fairly new Daewoo TV that has a high resistance neutral to DC ground path and when it is connected to a PC with the normal DC common to ground bonding it will trip a GFCI.

          26. User avater
            BillHartmann | Aug 12, 2008 11:43pm | #22

            You never indicated you removed the bonding screw.And you said that you used an ohm meter and it "beeped".What was the actual resistance. If it was more than 0.1 ohms then it is more likely in one of the branch circuits.And even if it is less than 0.1 it still might be in a branch circuit.
            .
            .
            A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

          27. arcflash | Aug 12, 2008 04:31am | #12

            Its hard for me to make out the first picture, but it appears that the grounding conductors (bare) are tied to a seperate bus. As long as there is no physical connection between the bare and white wire buses, and your bare wires are grounded to the panel enclosure (usually  done with a long green screw) then you are OK. The second picture is your meter base, and the ground and neutral are bonded together by basically just "sharing" a bus. The meter base has your first means of disconnect. What I don't see is NoLox, which protects the wire terminations from corroding, which is a code requirement.

            You will have to have the utility company shut of your power at the transformer in order to safely apply the NoLox. You can buy it at an electrical material supply house, and you just dip your stripped ends into the bottle before terminating them into the lugs. Anytime aluminum is used, you need NoLox.

            Other then that, and assuming I understood the pictures, you appear to be in good shape.

          28. Bpawb | Aug 12, 2008 05:02pm | #16

            Thanks, Arc...very observant!

            its hard to see....but it does have the nolox applied.

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