>The power company in my area offers a whole house surge protection system
which mounts behind the meter for $5 per month. I >recently had it installed
in my home. They installed a new meter ground rod which changed my ground
from 150 ohms to 65 ohms. In >talking to the installer I told him about my
ground at the tower which measured 120 ohms and the ground at my rig which
measured >195 ohms. Since I have 3 ground systems There is potential for a
problem.
Indeed you do, if you're worried about the electrical code, if nothing else.
>The tower grounds and the rig grounds are connected via the 5 coax shields
which are all grounded to the rod at the base of the >tower. . All the rig
and tuner grounds go to one point on the operating table and from there 10
feet to another 10 ft ground rod. The >rigs are also grounded through the
AC cords to the house ground. Question? Should I tie my central ground
point on the operating >table to the house ground via the ground on the 240
volt plug. Do I have a potential problem. Suggestions.
According to the code (which you can hew to or not, as you feel appropriate)
Ground rods must be interconnected by a suitable single wire, exothermically
welded. I don't have my code in front of me, but I think the interconnect
has to be either AWG6 or AWG10. This is for a low voltage system, so the
complete set of rules is a bit different, because the hazards are different.
The daisy chain grounding you've got through the power cords and rigs
doesn't meet the code requirement.
Should you ground your ground rod through the green wire ground? This is
more of a ground loop problem. You've already got the safety ground hooked
up through the equipment cords, and thence via your ground wire. You'll
essentially be creating another small loop.
Search the web for a "low voltage grounding book" by Mike Holt. It's a free
download, and worth reading. Discusses amateur radio antennae, satellite
dishes, networks, etc.
here are some online references:
http://www.imsasafety.org/journal/jan32002.htm
http://www.mikeholt.com/freestuff.php?id=freegeneral
>By the way the power company used a chemical welding device called a
oneshot GR1161G to weld the ground wire to the ground >rod. Its a small
ceramic tube which fits over the rod and burns gunpowder and a starter to
develop heat to make the weld. A neat little >device. He also used a 120
volt device like a big drill which drove the rod in the ground in 30
seconds. NEAT.
Exothermic welding... that's what's required by the code. The stuff burning
is actually a mixture of aluminum powder and copper oxide (aka thermite)..
the aluminum reacts with the oxygen in the copper oxide, leaving copper,
it's hot, so the copper is molten. It also removes the oxide from the
surfaces being welded. Same general scheme is used to weld railroad rails.
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See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
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