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Thread: does this make any sense

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  1. #1

    Default does this make any sense

    I am installing a "sub" circuit breaker panel in my garage. I recently discovered I have to install a second, isolated bus bar in the sub panel for the nuetral line seperate from the ground bar. ironicly the source for both bars can/will come from the same place. (the bus bar in the maine panel)
    i spoke to a licensed electrician who addmitted it makes no sense to him either.

  2. #2
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by jburton32 View Post
    I am installing a "sub" circuit breaker panel in my garage. I recently discovered I have to install a second, isolated bus bar in the sub panel for the nuetral line seperate from the ground bar. ironicly the source for both bars can/will come from the same place. (the bus bar in the maine panel)
    i spoke to a licensed electrician who addmitted it makes no sense to him either.
    If the electrician said that it made no sense to him either then I am saying that he ain't much of an electrician and maybe you should not ask him/her any more questions.




    Although this is not the best installation it does show how the equipment grounding and grounded (neutrals) MUST be installed.

    Note that the grounded (neutrals) do not land on the installed bar for the equipment grounding conductors. That would be a hazard in so much as the panel enclosure would then be part of a current carring conductor.
    Last edited by jwelectric; 05-08-2008 at 11:51 AM.

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    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    I think his puzzlement (mine, too) is that if you trace everything back to the main panel, the neutrals and grounds are tied together, so why not do it here, too? There have been repeated references to an article that explains why, but I can't find it right now.

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    Computer Programmer Bill Arden's Avatar
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    The rule is there for several reasons.

    1. if the neutral and ground are tied together at the sub panel and then the connection to the main is lost... all the grounds connected to the sub panel will become hot.

    2. Due to the current going threw the neutral there is a tiny amount of voltage on the neutral and thus tying it to ground can cause problems, ground loops ect.

    3. They love to make you spend more money.
    You have to run 4 wires instead of 3
    Important note Ė I donít know man made laws, just laws of physics
    Disclaimer: I'm a big fan of Darwin awards.

  5. #5

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    Also note that electrical panels have a "bonding screw" which connects the neutral bar to the metal case of the panel. For subpanels with a separate ground bar (which would be screwed into the metal case), the bonding screw should be removed from the separate neutral bar.

    And why should you do this separate ground / neutral bar thing with a subpanel?

    In general every single electrical code rule is in place because someone's home burned down or someone was electrocuted due to an electrical problem. Like those nightclub fires where many people die and then there is a big outcry from the public to prevent these things from happening again. Well they determine the cause of these things and then revise the building and electrical codes.

    Anyway if everything electrical worked properly forever, then a lot of things required in the electrical code would not be needed.

    BUT things break, wires come loose with time. Insulation on old wiring can melt due to heat or become brittle and fall off. This can be the case with old appliances.

    You can get a situation where a hot electrical wire is touching the metal case on an appliance.

    You can get a situation where the neutral wire on the main service panel comes loose. Actually this is not all that uncommon. Wires which carry a lot of amperage like a main service wire can become warm or hot if they are not torqued down correctly when installed (torque to foot pounds per label on panel). Then as you use and don't use electricity, the connection is hot/cold, hot/cold. The wire expands and contracts. Then works its way loose.

    Another common situation is for the main service panel ground wire to become disconnected. Plastic water pipe may be installed to replace metal pipe and the ground wire is not transferred to ground rods (required on new installs). A lawn mower may knock a ground wire loose. I saw a situation where a car scraped the side of a building and cut the ground wire.

    When the above situations occur or combinations of the above situations occur, modern electrical wiring installed to code will still protect you. Then there will be no tragedy and no need for a public outcry...

  6. #6
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    I understand and accept the possibility of the cases you mention, but other than IR-drop issues on the neutral and/or ground between the main and sub panels, I still fail to see why separating the ground and neutral at the subpanel is of any advantage. The only difference between 6 breakers in a subpanel, and the last 6 breakers on the main panel is, after all, the greater resistance of the "bus conductors" connecting these 6 breakers to the others.

    I'm not the sharpest crayon in the box, though, so I'll find the article I mentioned that goes into lots of detail in these cases, spent some time on Mike Holt's forum, study some more, and hopefully get it someday. (This is not to say I don't separate the ground and neutral in my subpanels -- I just don't know why I do, other than the Code says to.)

  7. #7

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    i spoke to a licensed electrician who addmitted it makes no sense to him either.
    It took me a while to "figure it out" too.

    If you lose the neutral, the current will find it's way into/thru water pipes, gas pipe etc.

    Of course if this happens at the service, the same thing will happen but they are tring to minimize the risk.

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