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Ground Rod Diameter vs grounding performance question

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Ground Rod Diameter vs grounding performance question BobK207 09-17-2006
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Posted by BobK207 on September 17, 2006, 2:41 am


If a small diameter ground rod (1/2" or 5/8") doesn't give the 25 ohms
(or less) to ground.....would a larger (3/4" or 1") diameter rod in the
same soil do better?

Is the soil the culprit or the soil / rod contact resistance? The
larger diameter rod contacts more soil..better grounding behavior?

cheers
Bob


Posted by RBM on September 17, 2006, 7:31 am
More surface area would give a better ground, so drive two rods six feet
apart and bond them together


>
>
> If a small diameter ground rod (1/2" or 5/8") doesn't give the 25 ohms
> (or less) to ground.....would a larger (3/4" or 1") diameter rod in the
> same soil do better?
>
> Is the soil the culprit or the soil / rod contact resistance? The
> larger diameter rod contacts more soil..better grounding behavior?
>
> cheers
> Bob
>



Posted by Paul Franklin on September 17, 2006, 7:41 am

>
>
>If a small diameter ground rod (1/2" or 5/8") doesn't give the 25 ohms
>(or less) to ground.....would a larger (3/4" or 1") diameter rod in the
>same soil do better?
>
>Is the soil the culprit or the soil / rod contact resistance? The
>larger diameter rod contacts more soil..better grounding behavior?
>
>cheers
>Bob

This is just opinion; I don't have facts to back it up...but..

The two are related. You have two resistors in series, one
represents the rod to ground resistance, the other ground resistance
back to the utility ground. The same factors that increase one (poor
soil conductance) influence the other. But I'm SWAGing that the ground
resistance back to the utility dominates most of the time. If you're
right on the hairy edge, a bigger rod might help enough. But I'd be
inclined to go with a longer rod, not larger diameter, because it
might get you to better soil, where a larger diameter rod just makes
more contact with the same (lousy) soil.

As I said, just conjecture on my part...

Paul


Posted by Ralph Mowery on September 17, 2006, 10:44 am

>
>
> If a small diameter ground rod (1/2" or 5/8") doesn't give the 25 ohms
> (or less) to ground.....would a larger (3/4" or 1") diameter rod in the
> same soil do better?
>
> Is the soil the culprit or the soil / rod contact resistance? The
> larger diameter rod contacts more soil..better grounding behavior?
>
> cheers
> Bob
>

The diameter of a rod has very little to do with the resistance of the
ground. The length will have a large effect. Ground rods should be
atleast 6 feet apart. Much closer and there is enough coupling through the
ground that the second rod does not reduce the resistance by very much.



Posted by Bud-- on September 17, 2006, 11:03 am
BobK207 wrote:
>
> If a small diameter ground rod (1/2" or 5/8") doesn't give the 25 ohms
> (or less) to ground.....would a larger (3/4" or 1") diameter rod in the
> same soil do better?
>
> Is the soil the culprit or the soil / rod contact resistance? The
> larger diameter rod contacts more soil..better grounding behavior?
>

The problem is the soil resistance. Increasing the rod diameter does not
change the resistance by much. I agree with other posts that increasing
the length with a longer rod or multiple rods is effective.

bud--

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