Re: Ground Rods (again)


Date: Sun Jun 23 1996 - 15:58:55 EDT

Grover and the group,
I got this back as bounced mail, so am reposting it in case it didn't make
the list. My appologies if it is a repeat. Darrel, WD6BOR

In a message dated 96-06-21 11:08:11 EDT, (Grover)

>Steven: Any reason why you could not put in four 3 or 4 ft sections, spaced
>about a foot apart and capped off with Ls and Ts. Seems to me it would give
>as effective a ground as a single 12 foot ground pipe?
> Lets hear from the "Gurus".

Grover and the group,

For ground rods to be effective they need to be spaced at least six feet
apart and no less than the length of the ground rod (8' rods = 8' apart). The
ground rod depth has much more effect than the rod diameter or even number of
rods due to the fact that each rod conducts through the ground resistance of
the soil around the rod. The soil resistance density is much higher in the
smaller volume directly around the rod so placing multiple rods close
together has the effect of combining the soil ground resistance instead of
providing effective parallel current paths.

As I said in a previous posting, the effectiveness increases with depth more
than with rod diameter. Soil chemical composition has a lot to do with the
ground system efficiency. Non-conductive soil types can be improved by
chemically teating the soil around the rod. The most common treatment is to
dig a 12 inch deep trench in an 18 inch diameter circle around the rod, then
fill with 8 inches of rock salt and cover with 4 inches of soil. It's
important to remember that you will also be sterilizing the soil so that
nothing will grow around the rod. Remember the Romans plowing their enemies'
filds with salt to starve them.

Ground resistance can also be measured with a Megger type resistance tester.
Ground resistance for electrical safety can be no more than 25 ohms according
to the National Electrical Code. Remember again that ground rods are for
electrical safety and RF grounds need to be established with radials or some
other ground plane type system.

The best way to drive ground rods is still to find someone else to do it.
Offer them a beer.

72, Darrel, WD6BOR

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