question about adding grounding to an old house

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Old 11-11-09, 01:07 PM
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question about adding grounding to an old house

Hi all, I live in an old house (built in 1923) that has no grounding system installed. It does have a panel installed later on with circuit breakers with multiple circuits. I am planning to add a grounding wire to every circuit that feeds back to the panel and wondering if it's good enough to just connect all the ground wires to the cold water pipe at its point of entrance to my house. This point of entry happens to be right next to the panel. Or I would need to connect all the ground wires to the neutral bus at the panel AND to the cold water pipe? Is it safe to do this? I read that this is how it is done nowadays, but would there be any hazards in doing so as the neutral wire carries return current back to the panel (in my house, it's going back to the power pole on the street, and then perhaps down to ground from there) ....and that the chassis of a computer which would be touched by me is physically connected to that neutral via the ground wire... Is it safe to assume that the return current would only go through the zero impedance path (the neutral at the panel that ultimately goes to ground at the power pole) and won't go through the ground wire also connected to the same neutral bus at the panel to a human touching the computer chassis while standing on the ground? It would appear 'safer' if the ground wires are all connected to just the cold water pipe and not to the neutral bus at the panel...Any pointers would be greatly appreciated... Civicfan8
 
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Old 11-11-09, 01:20 PM
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I am planning to add a grounding wire to every circuit that feeds back to the panel and wondering if it's good enough to just connect all the ground wires to the cold water pipe at its point of entrance to my house.
No. Must be to the panel ground.
Or I would need to connect all the ground wires to the neutral bus at the panel AND to the cold water pipe? Is it safe to do this? I read that this is how it is done nowadays, but would there be any hazards in doing so as the neutral wire carries return current back to the panel
If this is the panel with the first fuse or breaker (OCPD) then ground and neutral are combined and the answer is yes. If this is a subpanel the answerer is no. It goes to the ground bar only. Note: what you may think is a main panel may really be a subpanel because sometimes the first OCPD is incorporated into the meter can.

See also: http://forum.doityourself.com/electr...ng-ground.html
 
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Old 11-11-09, 03:12 PM
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Originally Posted by civicfan8 View Post
I am planning to add a grounding wire to every circuitCivicfan8
What you want to do is covered under the NEC 250.130(c). It is not really intended to add a ground to every outlet. It is meant for really only specific items, refrigerator, computer, etc.

You need to run it back to the panel and tie it into the grounding electrode system.

If you want to add new grounded circuit, OFF OF AN EXISTING ungrounded circuit, and using the appropriate cable you can ground them in this manner.

You also need to make sure the wiring is protected just the same as you would running new wiring. Which is really what the NEC wants you to do.
 
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Old 11-12-09, 04:47 PM
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Thanks for the replies. Now I see how a fault current could go thru the ground wire to the neutral at the main panel, and from there to the transformer ground out on the power pole, and this would trip the circuit breaker at the panel...

so essentially, since the equipment ground (computer chassis) is connected to the neutral bus at the main panel via the ground cable in the circuit, whenever I physically touch my computer chassis, this is equivalent to touching the neutral bus at the main panel? Is there any chance of getting shocked or electrocuted? I guess I don't understand why this would not be a hazard..is it safe to assume that this won't happen because of a higher impedance (my body) vs. a very low impedance (the neutral at the main panel)?

Thanks for your help in advance...

Civicfan8
 
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