"Roy Lewallen" wrote

Dave Shrader wrote:
. . .
A major point of caution is required. The NEC requires ONLY ONE ground
connection. Multiple ground connections introduce VERY SERIOUS ground
loops that may violate the NEC criteria. This opens a VERY LARGE loop
hole in your home owner's insurance policy. If you are adding a second
earth [ground] connection at your station use an isolation transformer
to break up the ground loops in the basic 120 VAC connection. Consult
with an electrician regarding your local and NEC codes.
. . .

My NEC book is getting pretty old now, 1990, but at that time, multiple
grounds were often not only permitted, but required. And a *minimum*
spacing was sometimes specified.

Outdated only regarding water pipe Roy, but good advice. And Dave's above
interpretation of NEC is a misunderstanding of the subject - easy to do so
consult a professional if you have any douvbt whatsoever about what your are
doing. Isolation transformers are not an option for isolating a station
ground from AC service entrance. They are permitted only in lmited cases
where independent grounding is required, and in other cases where HV
isolating transformers or fiber optic isolate feedlines. No one in this
group will likely have that requirement, so put that out of your mind Dave.
You *MUST* bond your station ground to the AC service main ground. Ignore
this at the peril of your entire system, which had better be 100% isolated
from all power and external feedlines and grounds. That is an option for
protection, isolating from *everything*. But it means unplugging and
shorting to ground all feedlines, disconnecting and removing RF ground
connections, disconnecting computer modems, telephone, and AC power to all
of your connected equipment. A really poor option in my opinion, because if
you forget something, or risk your life trying to disconnect during a
surprise thunderstorm, what was it worth?


For example, section 250-84, Resistance of Made Electrodes: "A single
electrode consisting of a rod, pipe, or plate which does not have a
resistance to ground of 25 ohms or less shall be augmented by one
additional electrode of any of the types specified in Sections 250-81 or
250-83. Where multiple rod, pipe, or plate electrodes are installed to
meet the requirements of this section, they shall be not less than 6
feet (1.83m) apart."

Or section 250-81(a), Metal Underground Water Pipe: ". . .A metal
underground water pipe shall be supplemented by an additional electrode
of a type specified in Section 250-81 or in Section 250-83. The
supplemental electrode shall be permitted to be bonded to the grounding
electrode conductor, the grounded service-entrance conductor, the
grounded service raceway, any grounded sevice enclosure, or the interior
metal water piping at any convenient point."

When I replaced the service (in 1979) in my 1952 house, the system
ground was a water pipe connection and I was required to add a ground
rod. Neither was considered adequate in itself; both were required by
the code at that time.

I agree wholeheartedly about consulting an electrician. Non-electricians
(including me) often have mistaken ideas about the content of the NEC.
It doesn't hurt to have an up to date copy of the NEC for reference,
either, if you anticipate doing any of the work yourself.

Roy Lewallen, W7EL

Jack Painter
Virginia Beach VA