Posted by David Sherman on Thursday, September 20, 2007 at 01:48:55 :
In Reply to: Re: Michael... posted by Kevin in Ohio on Wednesday, September 19, 2007 at 18:49:15 :
He was correct to make you disconnect the ground at the sub-panel. There is supposed to be only one ground at the main panel (service entrance). On that panel, and that panel alone, you bond the neutral to the box and the ground. All sub-panels have their grounds run back to the main panel and their neutral bus-bars isolated from their boxes. I assume that the point of this is to avoid currents flowing through the earth (rather than through the ground wire) under some fault conditions, but to be honest I can think of arguments for and against it. The utility distribution grid is grounded all over the place and they don't seem to be concerned about excessive earth currents. What they are concerned about is keeping the neutral pinned down to ground level everywhere.
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