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Old 09-11-2009, 08:46 PM   #16
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Panel ground and wire size


$10 got me an 8ft copper clad ground rod. It easily went thru 4ft of fill dirt to the bottom of my trench. After 10min with a 4lb hammer, it had maybe gone another half-inch. I am using the water soak now, but it does not look promising.

This entire area is sandstone. The deeper you go, the more like stone but tough. I used a demo hammer to trench for my conduit, and in sections, it was very slow going. I was told that some years back, a neighbor had to use dynamite to put in his swimming pool.

It would not be hard to braze a carbide bit on the end of the ground rod, or do it with some cheap threaded rod so the dirt can clear a bit.
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Old 09-12-2009, 09:43 AM   #17
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See if your local rental store has a heavy hammer drill (25 lbs or so) with a ground rod driver bit. I did my father-in-law’s pole barn with one. Got half the rod in the ground in less than a minute, then spent the next 15-20 mins driving the last 4 ft. It was going slow, but it went, and was able to get it 2” below the grass. One nice thing about the driver rod bit is that it usually doesn’t flare the rod so you can get the clamp on afterwards, though I put it first anyways…just in case.
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Old 09-12-2009, 10:07 AM   #18
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I actually ran the hose overnite
And I was using a 10 lb sledge
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Old 09-17-2009, 08:30 PM   #19
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After soaking the ground a couple of days, I was able to get within 14" of the goal but no further. That 10lb sledge was just bouncing off. It took a 40lb demo hammer to finish it off, but it took only a few minutes.

Now that its in, I don't like the ohmmeter reading I am seeing. The only way to make this ground more conductive would be to salt it.
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Old 09-17-2009, 10:28 PM   #20
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How are you taking resistance measurements? IOW, between what and what?
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Old 09-18-2009, 12:30 AM   #21
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Between the existing water pipe ground, and the top of my new unconnected ground rod. They are about 20ft apart at the closest point. The ground rod is vertical and full depth (8ft). The water pipe is at least 50ft to the street.

The soil is mainly sandstone. Sand is a great insulator.
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Old 09-18-2009, 10:44 AM   #22
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Concrete is conductive. It's a Ufer ground.

soil 30k to 50M ohm-meter
tap water 1M to 100M ohm-meter
salt water 0.2 ohm-meter
fresh water 1000 ohm-meter
concrete 200 ohm-meter
human body 5 ohm-meter
copper 20 nanoohm-meter

and

http://www.archaeogeophysics.org/wik...tivity_Results

I guess if you pass 10A or 20A into the ground and the voltage that you could be exposed to stays less than 300Ω(10 mA) = 3vac it's a "good ground".

Last edited by Yoyizit; 09-18-2009 at 10:51 AM.
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Old 09-18-2009, 10:53 AM   #23
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So do I understand that you're running (for test purposes) a cable from the water-pipe ground to the ground rod and measuring the resistance between those two points w/a multi-meter? What should the resistance reading between those points be? I'm not sure I have a grounding rod (I know... don't look at me) so when I get around to installing one I want to know how to measure if I did it correctly.
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Old 09-18-2009, 12:51 PM   #24
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I was taking my info from the following:

250.56 Resistance of Rod, Pipe, and Plate Electrodes. A
single electrode consisting of a rod, pipe, or plate that does
not have a resistance to ground of 25 ohms or less shall be
augmented...


Grounded, Effectively.
Intentionally connected to earth
through a ground connection or connections of sufficiently
low impedance and having sufficient current-carrying
capacity to prevent the buildup of voltages that may result
in undue hazards to connected equipment or to persons.


So on the one hand, the code seems to imply that a 'good' ground system will measure 25 ohms or less 'to ground', but I suppose this could just be describing the path to ground (wires, etc), but making no statement about the impedance of the soil itself. With that interpretation, I could just measure two rods driven a few inches apart as my standard. On the other hand, you need a complete circuit to carry current (soil included).

In the big picture, earth ground or ground potential is a reference local to where you are. My ground potential isn't the same as yours or even my neighbor's. For line safety, it seems the only ground I should care about is the one at the pole and the one at the panel, but I should care about the soil between them. For lightening protection, it would seem that higher impedance soils (insulator) would prevent strikes.

We need some big brain to pipe in and tell us how it is.
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Old 09-18-2009, 02:31 PM   #25
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Panel ground and wire size


Quote:
Originally Posted by wirenut1110 View Post
No but, our area isn't that rocky. Have had quite a few difficult ones but, none that didn't eventually give in. If it's hard in a spot, I just pull it up and try another area a foot away or so.

Just whatever you do, don't cut it off and take a hammer and flare the top so you can't tell you cut it off. Put your clamps on first too, cause once the rod flares out, it won't go on.
In NYC (since we joined the NEC and the Ground rod is a requirement in all NEW jobs or UPGRADES) the Inspectors carry a device where they can measure how deep the rod is buried. (Now more than ever)Don't Drink and Drive!!!
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Old 09-18-2009, 02:53 PM   #26
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Pass heavy fault current into your grounding system.

With separate leads measure the voltage between
a cold water pipe farthest from your water inlet line and
a ground/neutral pin on an elec. dryer outlet with the dryer off.
You're using the dryer lead as a long test lead going directly back to your panel.

Copper pipe should measure about 0.18 ohms/1000' so a 10A fault current through 100' of pipe should give you about 180 mV drop.

The tap water flowing through that same pipe should read k x 10^9 ohms, where k varies from 2 to 240, so I guess a volume of water of this shape cannot effectively ground you.

BTW, there is already current flowing through the ground, so if you measure the AC voltage between two grounded points and then load that voltage down with a resistor such that the voltage is halved, the resistor value = the ground resistance.
The wider the bandwidth of your AC voltmeter the more volts you will read.

There might even be DC flowing in the ground.

If you want your readings to correspond to industry-wide accepted values you probably need to get your hands on one of Fluke's meters that are designed to measure ground resistance.

Last edited by Yoyizit; 09-18-2009 at 03:46 PM.
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