Old house...no ground wire

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  #1  
Old 06-07-02, 09:44 AM
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PJMorgan
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Old house...no ground wire

I am looking to replace my dining room and entry hall lights. The new lights have a ground wire.....the old fixtures do not. I know that I can connet the ground wire to any metal in the area if available.....but what is the best way to do this? Is it safe to drill a hole in the plate and place a screw in it for the ground wire?
 
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  #2  
Old 06-07-02, 02:12 PM
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FREDDYG_001
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PJMorgan, If the ceiling outlet box is metal their should be a 10/32" threaded tap in the bottom of that box for a green ground screw(Home Depot sells them). If not , just wrap it around one of the NM cable clamp screws in the box.





Fred
 
  #3  
Old 06-07-02, 02:26 PM
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FREDDYG_001
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PJMorgan, You also said this is a old house and if this house has shallow (pancake) boxes(usually means armoured cable wiring), you can drill and tap the box (10/32) for a green ground screw. Sheetmetal screws are not an approved screw for grounding as per NEC. If that light came with a cross bracket their should be a green ground screw with the bracket



Fred
 
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Old 06-08-02, 12:20 PM
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cajon ken
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Just because you connect the ground wire to a metal box it does not mean that it is grounded. You must be sure that the ground SYSTEM goes all the way back to the panel and out to the ground rod.
 
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Old 06-08-02, 12:28 PM
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Actually, the equipement grounding goes all the way to the panel and out to the power company transformer. The ground rod, although an important part of protecting your electrical system, serves no purpose for grounding your outlets.
 
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Old 06-08-02, 01:13 PM
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Wgoodrich
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I suspect this is a prime example of using a generic term "ground" for both grounded and grouding.

First off if you have a non grounded electrical system [electrical system without an equipment grounding conductor] then you may replace your light fixture with the green wire just folded into the box not connected to anything as a minor repair to an exixting ungrounded electrical system [two wire electrical system with only a black and white wire but not bare or gree wire.

Second you stated that you know that you can connect to any metal nearby. The NEC forbids you to connect an equipment grounding conductor [green or bare] to any metal part such as water pipes within the house. The NEC requires that if you install an equipment grounding conductor to a box without an equipment grounding conductor you must run a green insulated grounding conductor from that box directly to the main service panel's grounding bar. Never connect a green equipment grounding conductor to a metal water pipe, the NEC forbids this connection as discribed.

John is right a grounded conductor [white wire] is the return path back to the main service panel and then back to the center tap of a transformer.

I suspect the use of the term ground conductor lead John and the person making the post down two different paths with one talking of an equipment grounding conductor that is bare or green and the other talking about a white grounded conductor that is the return path of a 120 volt circuit that completes that 120 votl circuit required to make a 120 volt circuit work.

Hope this helps

Wg
 
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Old 06-08-02, 04:32 PM
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No, I really meant the equipment grounding conductor. In the event of a fault causing current to flow through the equipment grounding conductor, that current does not flow into the ground through the grounding rod. It flows back to the power company transformer. That was my only point. The grounding rod is not fundamental to the operation of the equipment grounding conductor (the bare wire in most circuits).
 
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Old 06-09-02, 12:43 PM
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Wgoodrich
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cajon ken said;

Just because you connect the ground wire to a metal box it does not mean that it is grounded. You must be sure that the ground SYSTEM goes all the way back to the panel and out to the ground rod.

John Nelson said;

Actually, the equipement grounding goes all the way to the panel and out to the power company transformer. The ground rod, although an important part of protecting your electrical system, serves no purpose for grounding your outlets.

Seems like a discussion has split from the original question to where the equipment grounding conductor carries current back to when a dead short appears.

In my opinion both cajon ken and John Nelson is partially right.

While in principle if power comes from a transformer the shorted current will travel back to a definite degree to the center tap of the transformer on the service neutral conductor and neutral service drop conductor. If the power comes from that transformer then the power tends to be sucked back to that center tap of that transformer rather than take an alternative path avaialbe.

The part where cajon ken is partially right is the fact that the neutral service conductor is married to the grounding electrode conductor going to the ground rod creating a path to both the center tap of the transformer and the grounding electrode. However I believe John's point is trying to make is that the current will travel to a definite degree back the the transformer where it came from. However it is possible that some current may travel from the main service rated panel where the service neutral and the grounding electrode conductor is married down that grounding electrode conductor into the earth.

We must remember that the ground rod is a made electrode and is probably the worst grounding electrode design of all those listed by the NEC as approved grounding electrodes.

While the equipment grounding conductor is married to both pathes [center tap of the transformer or the earth the electrical current will take its easiest path which most definitly would be the center tap of the transformer.

The grounding electrode conductor is primarily installed to provide assistance to obsorb high current entities such as lightening. Remember lightening is not deriving its power source necessarily from the transformer but that lightening may pull its power source from the sky or from the earth or from the utility lines or any other source that has created a difference of potential enough to create the lightening bolt. Lightening is so unlimited in its degree of power that excessive current may travel down both the grounding electrode conductor and the service neutral conductor.

I can not disagree with what John is trying to point out. The ground rod may take some of the current of an electricla short produced by a transformer as a power source but most the current will travel back to the center tap of the transformer.

Wg
 
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