Proper length and burial of grounding rod.

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  #1  
Old 08-12-07, 02:47 PM
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Proper length and burial of grounding rod.

I was recently digging next to my house. As part of the excavation, I dug up what I think is a grounding rod. The rod was about 18" long and was completely underground. There is a wire with a with sheath (14 gauge?) connecting from the rod to a gas pipe via a hose clamp. When I was reburying the rod, the white sheathed wire broke loose from the hose clamp.

I know that I have a heavy gauge, sheathed grounding wire that goes from the service panel to the same pipe (deeper in the ground).

Questions:

1) I read in my Stanley Complete Wiring book that a grounding rod is 8 feet long. Do I need to replace this rod with a longer one? Or, should my sheathed grounding wire from the panel to the gas pipe suffice?
2) If I use the existing rod, how deep does it need to be buried?
3) Is a hose clamp adequate to connect the wire to the rod?
4) Should I use bare copper, as it is used for grounding in other applications?
5) Any guess why the short rod would be used when it seems the heavy gauge grounding wire should suffice?

Any insight is appreciated.
 
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  #2  
Old 08-13-07, 10:26 AM
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> connecting from the rod to a gas pipe via a hose clamp.

Gas pipe or water pipe? If it's actually the gas pipe, it should not be used as a grounding electrode at all. If it's a water pipe then it must be used as a grounding electrode.

> I read in my Stanley Complete Wiring book that a grounding rod is 8 feet
> long. Do I need to replace this rod with a longer one? Or, should my
> sheathed grounding wire from the panel to the gas pipe suffice?

The grounding wire from your service panel (called the GEC), should not connect to the gas pipe at all. It should connect to the metal water pipe (usually just inside the home), and at least one ground rod. Ground rods are 5/8" x 8' copper clad and should have an acorn clamp, not a hose clamp.

> If I use the existing rod, how deep does it need to be buried?

Don't reinstall the old rod. Is it possible the small rod goes to your cable TV or phone service? Sometimes installers of those services will drive a new small rod if they can't easily access the primary ground rod. If so, the phone and cable services should be correctly grounded to the primary electrode.

> Should I use bare copper, as it is used for grounding in other applications?

Doesn't matter.

> Any guess why the short rod would be used when it seems the heavy
> gauge grounding wire should suffice?

The rod is used to reach a depth where the soil is always wet, so an 18" ground rod would be worthless unless you live in a swamp. :-)
 
  #3  
Old 08-13-07, 12:13 PM
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Thanks for the response.

The small wire from the rod is definitely connected to a gas pipe (the pipe is connected to the gas meter).

I'm pretty sure the GEC is also connected to the same gas pipe. Definitely NOT connected to the water pipes, though there may be an additional grounding rod. I'll have to dig around some more to see where the GEC connects. I know I saw the connection previously, but I didn't pay it much mind except to avoid messing with it.

>Is it possible the small rod goes to your cable TV or phone service?

Could be. But the rod doesn't connect to anything but the gas pipe. If it were for the telephone (which enters the house in the general vicinity of the power and gas lines), wouldn't there need to be a connection from the rod to the telephone box?
 
  #4  
Old 08-15-07, 08:19 AM
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There are 2 separate issues that are often combined: grounding and bonding.

Grounding is the connection of your electrical system to earth ground.

Bonding is the connection of something that might become energized back to your electrical system, so that electrical contact with this thing will cause a short circuit and open a breaker.

Metal underground water pipes are very often used as 'grounding electrodes' to ground your electrical system, and they must also be bonded for shock protection. Usually a _single_ wire between your water pipes and your panel serves _both_ purposes.

Interior metal gas piping is _sometimes_ bonded.

External metal gas piping is never supposed to be used as a grounding electrode. Usually there is a dielectric (insulating) fitting at the gas meter, to prevent the interior _bonded_ piping from inadvertently using the external gas pipe as a grounding electrode.

If you have a connection between your electrical service and the gas pipe, 'downstream' of the gas meter, then this is probably just required bonding. If you have such a connection 'upstream' of the gas meter, then you may have a problem with your gas pipe being used as a grounding electrode.

I wonder (but do not know) if the small 'ground rod' that you found was a 'sacrificial anode' being used by the gas company to protect the underground gas pipe. If this guess is correct, then that is not a ground rod, but instead a bit of reactive metal (Zinc or Magnesium) electrically connected to the steel pipe, so that the anode corrodes while protecting the steel. You should probably check with your gas supplier.

-Jon
 
  #5  
Old 08-16-07, 05:40 PM
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Grounding old service

My parent's home was built in 1953 and has a two wire system in the service boxes, and in all of the outlets and fixtures. Since all of the wiring I have done in my past has been with 3 wire service boxes, Im a little concerned with how to best modify and upgrade this system safely. The always present bare copper wire that was hooked to my water pipes in my other homes, is not present here. I suppose that if I replaced the service box with a new one, I could run the bare copper over to the well water pipe and and just work my way out from there. It seemed to me that the electrical service lines coming in from the power company were just two wire anyway even in the other homes.
 
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