At 09:13 PM 10/7/2005, Tom Rauch wrote:
> > >The neutral wire IS to be grounded to earth along with
>the safety ground
> > >at the service panel. Both are tied together and
>connected to earth
> > >ground at the main service panel. The power company also
>grounds the
> > >neutral connection at the transformer to earth ground.
> >
> > Not necessarily.. for the same reason as you have a single
>interconnect
> > between neutral and ground. You don't want neutral return
>currents flowing
> > back to the transformer via the ground path.
>
>Code in Ohio and here in GA is that the service entrance
>panel be grounded to earth ground. I've never seen a case
>otherwise, and I can't imagine why they wouldn't bond the
>neutral to the safety ground at the mains panel.
>
>It would be a real safety issue to not ground the neutral
>and safety at some point in the system.
I think the question is not whether you'd ground the neutral at the service
entrance (that's what the code requires, anyway), but whether the standard
practice is to also ground the neutral at the distribution transformer.
I can see reasons to do it either way. I've also seen installations done
both ways (but they're installations that were done over decades, and who
knows who was tinkering along the way, not to mention code and practice
changes over that time span...)
>I *think* code here says distribution panels should have the
>safety ground from the main feed panel isolated and brought
>to the distribution panels in my outbuildings.
The code would mostly be concerned with the neutral/ground bond ONLY
happening at the service entrance (main feed).
The grounding would be a normal sort of tree thing, all eventually winding
up back at the bonding point. You could have as many other grounds along
the way as you want (for instance, the conduit might be grounded), the only
requirement being that all those grounds have to be interconnected.
>I don't do
>that. I won't do that. I actually treat my distribution
>panels in different buildings as new mains. Each building
>has a service entrance ground that bonds to the neutral in
>each building.
If in a single building, that would be a no-no. In multiple buildings, I'm
not sure. The rules ARE different when you're talking about physically
separated structures. It probably depends on how the feeders are structured.
>The safety ground comes from there.
>My house actually has the service entrance ground at the
>light meter bonded to the halo around the house, and it is
>tied back with flashing to the breaker box ground some 15
>feet away with 4" flashing. That ground comes under the
>crawl to my radio room entrance. The distribution panel in
>this room bonds to that flashing, all the cables bond to it
>also.
>
>There really isn't a safe way to do otherwise for lightning.
>I can't risk having panels floating from earth or not being
>bonded to lightning grounds.
And the NEC would require the same thing, I think. That's why they have
the "all grounds bonded together" rules.
The tricky thing is the neutrals. The concern is with neutral return
current flowing through a ground instead of through the neutral wire, where
it should. But, when you have separate structures, bonding the neutral to
the ground at each structure might make sense. It's kind of like the
separate N:G bonds at each house when they're all fed from the same
transformer.
When these sorts of things come up in the design process, and the code's
not real clear, there's a standard "out": Consult the AHJ (Authority
having jurisdiction).
>73 Tom
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