sub panel bonding question

HI I am replacing an old subpanel in my garage. The old panel has the neutral and grounds attached to the same bar. The new panel has separate neutral and ground bars, but has a screw to bond the neutral to the ground, if desired. When bonded it would be wired like the old panel. I am going to install it bonded, like the present hook-up, unless someone can tell me why it would be better to leave the neutral isolated from the ground.
Thanks
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The grounds and the neutrals in a subpanel MUST be separated from each other. They are only connected at the service entrance which in many homes is the main panel.
If the neutral conductor for the subpanel ever broke loose while it was bonded to ground, the grounding conductor would carry the current. That means that all metal (Conduits, panels, electrical boxes, water pipes, gas pipes, etc.) between the subpanel and main panel will be energized with the neutral current. It is also a code violation to connect the neutral and grounds together in a subpanel.
John Grabowski http://www.mrelectrician.tv

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Thanks so much I guess I won't install that bonding screw.

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How many wires are feeding the subpanel? 4-wire, I hope {2 hots (black and red), 1 neutral (white), 1 equipment ground (bare or green wire or a metal conduit)}. If the feeder for the subpanel is 3-wire with no metal conduit, removing the bond screw will create a hazard too. The feeder to the subpanel needs to be 4-wire.
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Is this sub panel in the same structure as your main panel? If so, the neutral and ground should not be bonded, they should be seperate. If your sub panel is in a detached structure, and if these 2 structures are not connected by water pipes, etc... then the neutral and ground should be bonded, and a ground rod installed. You didn't say which was your case. Proceed with caution. Dave

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Thanks for all the replies hear is more info. Sub panel is in a detached garage. It is fed with 3 wires (2 hot 1- neutral) from the main panel in a separate house. Subpanel has it's own ground stake so there are 4 wires going into the box. From what I have read here I guess I should bond the neutral with the ground?

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Yes, as long as there are no continuous metallic paths between the buildings......water lines, gas lines, coax cable, etc. so that no parallel paths for the neutral current are created.
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volts500 wrote:

If there are other ground paths connecting the 2 buildings, you need to remove the bonding screw and run a 4th ground wire from the panel that feeds the outbuilding, *or* (and this is just my interpretation) tie that outbuilding's ground rod to the main buildings grounding electrode system with a #6 or larger copper wire.
If the neutral wire in the feeder is the only grounded path connecting the 2 buildings, you bond the ground and neutral at the outbuilding -- the outbuilding panel is service equipment.
Best regards, Bob
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www.homewiringandmore.com. There is a lot of information on that site that may put your mind more at ease. There is also a bb moderated by a master electrician and former electrical inspector for the state of Indiana. He will give you authoratative answers pertaining to your particular situation. It's an awsome site for homeowners wanting to learn more about wiring. No charge for using the site. He just wants people to do things safely.
Dave

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I have a different question/problem. I'm building a garage/studio with power coming from my barn but am running a water line from my house. The garage/studio has a ground rod installed. Do I need to run a ground wire in the trench with the water pipes to connect the house to the garage/studio even if the power is comming from the barn? The house main service panel and the barn main service panel are fed from the same meter at the barn so there is a ground wire from the barn to the house.
Ted
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Install a plastic (polyethelene or PVC) water pipe. If you haven't run the wires yet, a 4-wire feeder is always preferred over 3, except for cost. With only 3 wires and a metal pipe, you're making a nice current loop between the buildings over that pipe.
--
Mark
Kent, WA
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