John wrote:
>I generally just monitor the reflector, but there have been two topics
that I
>have been paying close attention to:
>
>1. Grounds.
<snip>
>B. AC Ground- Most homes have a grounding rod driven into the ground near
the
> service entrance. From the grounding rod to the distribution panel is a
>wire, generally green. This green wire travels throughout your home to every
>receptacle, light switch, lighting fixture, your electric stove and
refrigerator.
>This is probably the biggest ground loop known to mankind and undesirable
in Ham Radio. For
>Ham Radio, all of your 120vac devices should be plugged into ONE receptacle.
>The green wire that was installed when your home was built should be
removed.
>In its place a new green wire should be installed and ran outdoors to a new
>ground rod. <snip>
Although that'd be nice from a HAM Radio perspective, it'd be totally
against NFPA/IEEE recommendations and forbidden by National Electric Code,
unless your hamshack is a building which is physically separated from your
service entrance... in which case, the separated building's service panel
must have an AC ground rod of it's own.
To add specific note, the AC service panel's grounding wire must originate
AT the service panel, pass THROUGH (unbroken) the meter box's grounding
lug, and continue down to several inches below grade, then extend outward
from the building by a minimum amount, to a copper-clad steel rod 8' long,
fastened by non-corroding clamp rated for direct-bury use. In cases where
rock is shallow, it's commonly accepted by building inspectors to have the
rod driven into the ground at up to a 45 degree angle to allow a long rod
to bury in shallow dirt, however, I took TWO 8' rods, cut each off at 4',
and ran ONE conductor continuously through ALL FOUR rods, spaced out by 8',
to yield compliant grounding.
In order to pass NEC, ALL ground rods must be bonded together, with only
ONE grounding entrance to the building... that means you can't have a
separate local ground. This is to prevent one of your radios, or an
electrical conduit, from becoming a superior ground path should your
primary point suffer a ground fault... or one of your machines end up with
AC leaking onto the new ground rod.
I was able to accomodate NEC requirements by using the method recommended
in ARRL handbooks for the last 20+ years- running a complete copper loop
around the tower and shack, with rods spaced at regular intervals... with
radials submerged as the yard permitted. Note that my local inspector had
no problems with additional ground radials or their method of connection to
the tower, nor my shack bonding plate, so long as my AC
panel-to-ground-rods were connected with continuous conductor.
The unfortunate part to NFPA/IEEE/NEC rules, is that they make very little
distinction between grounding conditions- essentially just AC and
lightning. RF counterpoise is essentially ignored. The rules include
requirements which are sensible to modern living, but not feasable under
situations where AC and RF leakage occur- namely, the required
implementation of Ground Fault Circuit Interrupters. GFIs, for the most
part, don't tolerate the presence of leakage, be it AC (hot-chassis
devices) or directly connected, or proximity-induced RF. I was confronted
with this situation, and rather than attempt to educate the building
inspector, I simply installed GFI-equipped circuit breakers in the power
panel, which I replaced with conventional units after he left. Simply
keying up a 6m AM rig was enough to trip the GFI. Adding ferrite beads to
all three leads (hot+, hot-, neutral, and ground) of the 220vac subpanel
service prevents RF from being carried out of the shack, to the primary panel.
Although dropping the primary ground is a simple answer, it's potentially
lethal (oh man- bad pun- sorry), and in the case of a phase- or
neutral-loss, or lightning strike on your power utility, will definately
cause immediate damage to equipment and risk of fire.
DK :-)
73's from KW0D Dave in LeClaire, Iowa
|