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Thread: outbuilding with 3 wire subpanel...I'm still confused...help?

  1. #1

    Default outbuilding with 3 wire subpanel...I'm still confused...help?

    Hi everyone this is my first post but I've lurked around in here reading other posts for awhile. I have a question that I know has been asked before but I'm still kinda confused. Here goes...

    6/3 (h/h/n w/o ground ) feeds a subpanel in an unattached barn (100ft from the house). The 6/3 is not in a conduit and no other connections to the barn exist. I'm a new owner and I'm guessing this was put in years ago.
    The neutral bar has both neutrals and grounds bonded. The neutral bar is not bonded to the box.
    I checked the outlets in the barn with a 3 prong outlet tester and they check as being wired correctly. I've read other posts that say the grounds and neutrals need to be separated as of the 2008 NEC.

    I put a ground bar in the subpanel now and plan on separating the 2 (leaving the neutral bar floating) and putting in a grounding rod for the ground bar. Is this the right way to go at least for now until I can run 4 wire?
    I've read the old NEC allowed 3 wire to be used and neutrals and grounds to be bonded. The 2008 NEC does not allow this. This is where I am confused. I just want it to be safe. Is the way it is better than grounding it with a rod and separating them? Thankyou in advance. - Roger

  2. #2
    Electrical Contractor/Instructor jwelectric's Avatar
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    With the three wire installation that you have now the neutral, equipment grounding conductors, the panel enclosure and the grounding electrode must all bond together.

    Under the requirements of the 2008 code cycle three wire installations such as you have would be non-compliant. The 2008 cycle requires that an equipment grounding conductor be included with the feeders and the neutral be isolated at the remote panel board.

  3. #3

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    Thanks for the quick reply. Ok so I need put in the screw that bonds the neutral bar to the panel? I'd like to change the wiring to 4 wire in the spring.

  4. #4

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    When you install the 4 wire line, THEN isolate the grounds and neutrals, but for now BOND everything together including the metal panel.

    You would want a good electrical connection from the grounds back to your main panel. If there was a short from hot to a ground, you would want this to trip the breaker in your main panel (should a breaker in your subpanel not trip or a main wire short to ground).

    If you just had the grounds connected to a ground rod ONLY at the barn and no ground wiring going back to your main panel, then this would not be a good connection (via the earth) back to your house and I don't suppose it would trip the breaker?

    (After installing the 4 wire, remove the neutral bonding screw at the subpanel and then the ground bar would of course be bonded to the subpanel...)

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