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Grounding in USA residential homes with 240/120 panel

by psparky
Tags: grounding, homes, panel, residential
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psparky
#1
Mar17-13, 10:00 AM
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I asked the question during a grounding seminar ....talking about grounding in USA residential homes with 240/120 panel. I wasn't quite satisfied with the answer.

The question is.....what dangers are introduced when you remove the ground rod from a service entrance like the main panel in a home. And lets assume water line is not used as a ground so the ground is completely floating.

Here are my thoughts:
I believe the breakers are still going to pop in a hot to ground situation due to tying the neutral and ground together in the panel......so any short will hit the center tap of transformer and trip breaker regardless of earth rod or not.

Someone mentioned the voltage may drop in panel....not sure what that's about. Someone mentioned voltage may be higher....someone mentioned you may end up using your neighbors ground rod.......all heresay at this time.

We are clearly going to lose lighting protection.

One danger I can think of is that these appliances need to shed trickle current due to any leakage inside or even static charges. So normally, ground bleeds any of this. Without ground...deadly charges may build up.

And to add more confusion....let's talk about 3 phase feeders (NO neutral) on a aluminum ladder in a factory. When grounded properly.....when hot wire touches ladder....we pop the breaker. But how is this current returning? Is it going thru the ground all the way back to the electric company? Or is something else happening?

I'm guessing there is trickle current all over the place. If you think about a 500 KV line coming down the power lines.....those insulators on the towers have a resistance of a finite number rather than infinite number, Since V=IR.......small current must leak down any insulator into the ground. Even just a 12KV line must be leaking even a little at any insulator. Again, does this leakage go back to the source...electric company?

Can anyone enlighten us further on the subject?
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dlgoff
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Mar17-13, 02:04 PM
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There are reasons other than faults.

jim hardy
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Mar17-13, 04:01 PM
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The question is.....what dangers are introduced when you remove the ground rod from a service entrance like the main panel in a home. And lets assume water line is not used as a ground so the ground is completely floating.
You already know that answer.

Per Don's sketch every appliance in the house now has its skin hard wired to the centertap of the service transformer atop backyard power pole.
That point is earthed by the bare copper wire on side of pole. It is coiled on bottom of pole to give good surface area..
So every appliance skin is elevated above earth by the voltage drop along that neutral wire from your panel to pole. When things are going right it's so small you'd probably not notice.

When lightning strikes the top of that power pole, every 'grounded' appliance in the house is connected directly by wire to the bottom of a lightning bolt.
Were your house's ground rod intact, the earth's potential at your house would be driven up toward that of the lightning bolt so there'd be little potential difference between your feet and that appliance skin.
Without that ground rod you lose that protection. If you're touching an appliance you will feel voltage difference between whatever you're standing on and the bottom of that lightning bolt.

Granted lightning is rare. But a transformer can fault primary to secondary, or a high voltage wire can fall across your incoming power wires. Same principle applies.

The lightning thing happened to me once, I was out in the yard using a metal cased drill on a 3 conductor extension cord, but fortunately was standing near my house ground rod(20 feet or so). Still the shock was substantial.
Maybe there's something to be said for "double insulated" power tools with plastic cases..

old jim

dlgoff
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Mar17-13, 07:52 PM
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Grounding in USA residential homes with 240/120 panel

Quote Quote by jim hardy View Post
... every appliance in the house now has its skin hard wired to the centertap of the service transformer atop backyard power pole.
That point is earthed by the bare copper wire on side of pole. It is coiled on bottom of pole to give good surface area..
So every appliance skin is elevated above earth by the voltage drop along that neutral wire from your panel to pole. When things are going right it's so small you'd probably not notice.
It only takes once when things aren't going right to notice.


because
dlgoff
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Mar17-13, 08:14 PM
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The correct way just for "those who want to be safe" image.



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