grounding electrode questions

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  #1  
Old 11-27-05, 04:18 PM
rob
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grounding electrode questions

Hi - I noticed that the grounding electrode (in the ground) outside my house (built in 1965) near the service entry has no wire connected to the acorn clamp. Also, this is a 3/8" diameter rod. There is a #12 copper wire clipped to the outside of the service entry door (just overhead), that I suspect was once connected to the grounding electrode, but is now connected to the coax TV cable that enters the house in the same area. I have several questions.

I am considering installing a new 5/8" or 3/4" rod with thicker ground wire. Should the ground wire run from the breaker panel in the garage or from the service entry box, or both.

(I'm assuming that the #12 wire going to coax cable is not particularly useful or correct.)

Also, service comes in from under ground to the outside service entry box, and the main breaker panel is mounted inside the garage, probably about 25 feet from the main service entry.

I don't think I want to open the service entry box myself, but if it's running a ground to the breaker panel in the garage, I would do that. I'm mentioning this because even if I don't do this work myself, I want to know what work should be done, so that it's done properly.

Thanks!
 
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Old 11-27-05, 04:24 PM
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You would need to run a #6cu from the rod to the MAIN breaker enclosure.
Are you SURE the main is 25' inside the garage? There is no main breaker/disconnect outside?
 
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Old 11-27-05, 04:36 PM
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clarification

Hi Speedy - Maybe my "terms" aren't correct. There are only 2 panels, the one outside where service enters the house where the meter is, and you can shut off power to the whole house from there. The other panel is where the indivual circuit breakers are for the whole house, which is located in the garage.

That said, is the MAIN you are talking about the one on the outside of the house where service enters?

The clip to the box isn't correct, is it?

Thanks
 
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Old 11-27-05, 05:10 PM
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The disconnect outside is the main and this is where the GEC (grounding electrode conductor) must go.
You MUST be very careful in this box as it has unfused conductors which cannot be turned off unless your POCO comes out to do so.

"The clip to the box isn't correct, is it?"
Sorry, I don't understand what you mean.
 
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Old 11-27-05, 06:05 PM
rob
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internal GEC?

Ok, thanks.

I looked at my neighbors house. There isn't a grounding electrode visible on the ground. Is it possible that these houses used internal electrodes? If so, how would you know? Open up the main and see if there is a lone GEC going into the ground?
 
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Old 11-27-05, 06:17 PM
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Many older homes had no ground rod. They just used the water pipe feeding the house.
 
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Old 11-28-05, 09:25 AM
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checking the ground

Is there a way to tell how "good" this ground is? Do you need a special meter to check it?
 
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Old 11-28-05, 11:20 AM
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To check a ground rod you need special metering equipment. Most electricians don't bother; they simply place two ground rods and call it good. Using the metering equipment would generally require driving reference ground electrodes, disconnecting your ground rods, etc.; not a DIY task.

The #12 clipped to the outside of the box is the ground _for_ the cable TV, and given no other information it should stay exactly as is. (CATV installers are notorious for installing their ground bond incorrectly, but it should be there, and nothing that you've said suggests that it is improperly installed.)

Do you have a particular problem or symptom that makes you suspect a grounding issue?

-Jon
 
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Old 11-28-05, 11:31 AM
rob
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Hi Jon - The reason I started down this path was because I saw the grounding electrode in the ground with nothing attached to it except an acorn clamp but no wire. Then I started to wonder what was going on. I noticed that my neighbors home didn't even have a grounding electrode. So, maybe as speedy suggested, the houses are grounded to the water pipes.

So, then I questioned 2 things:

1. Is there a way to verify that a good ground exists?

2. If the water pipes are being used, wouldn't it be better to have a grounding electrode installed.

Thanks
 
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Old 11-28-05, 11:51 AM
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You would need to locate the grounding electrode conductor at the service disconnect, and follow it to the grounding electrode. This will be a wire, at least #6, and quite possibly larger (depends upon the particular grounding electrode used, and also on physical protection, etc.) that should go from your 'meter-main' to the actual electrodes used. The only practical way that you can determine the state of things is a visual inspection of the grounding electrode conductor. If you want to spend a couple $K on test equipment, you could test the ground rod.

It used to be that the metal water pipes entering your home were considered sufficient, and that you could connect the GEC to any convenient location on the metal water pipes.

_Current_ code requires the following: if you have metal underground water pipes entering your home, then they _must_ be used as one of your grounding electrodes. The GEC must connect within 5 feet of where the pipe enters your home. In addition, you _must_ have another grounding electrode, usually a ground rod. In addition, the ground rod must have a resistance to ground of 25 ohms or less, _or_ you must install a second ground rod. Since it is a pain to measure ground rod resistance, most electricians use two ground rods.

It _may_ be that the grounding electrode that you found is supposed to be connect to your service, but the wire came free. You might not see the grounding electrodes at your neighbors' because they could be buried.

Another possibility is that this is a ground rod for some other service (phone, CATV, etc.). If this is the case, then the ground rod was installed improperly, because these other services are supposed to share the same grounding electrode system as your electric service. But driving a 'separate' ground rod is one of the ways that installers of CATV and phone sometimes get things wrong.

-Jon
 
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