[Elecraft] Grounding negative side of power supply?

[Edward Cole]

------------------------------

Message: 26
Date: Tue, 20 Apr 2010 06:31:04 -0400
From: "Tom W8JI" <w8ji at w8ji.com>
Subject: Re: [Elecraft] Grounding negative side of power supply?
To: "Bob McGraw - K4TAX" <RMcGraw at Blomand.net>, "Jim Brown"
         <jim at audiosystemsgroup.com>,    "Elecraft List"
         <elecraft at mailman.qth.net>
Message-ID: <321074F178104F4FAB7715A73E6D11CF at radioroom>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
         reply-type=original

<Refer to the NEC.  It's their rule.

As a side note, a loss of property covered by insurance may
be dissallowed
if they find improper grounding contributed to the damage.
And they
reference the NEC with regard to "proper".>

I'm not so sure we aren't getting carried away with our own
interpretation of NEC rules here. We also have to apply a
little technical "common sense" to our systems.

I have antennas and towers scatter over thousands of feet
distance. It would be totally worthless and physically
impossible to bond the ground rods on my antennas to my
mains ground. The additional protection to my house and
equipment, and to people, would be zero.

In addition to no improvement in protection, the
effectiveness of the low-noise antennas would be greatly
decreased.

Then we have to consider odds that power lines, trees, and
our large towers would be ignored by lightning and a small
ten-foot-tall  twenty-foot-long, antenna would be struck. If
it were struck, where would the majority charges move? In
the feeder to the house. If the feeder ground were bonded to
the mains ground at the building entrance, the safety issue
for people and the dwelling is closed at that point. The
ground at the dwelling entrance, that is mandated by NEC to
be bonded to the mains ground, is key to safety. Not the
critical signal ground at some backyard clothesline antenna.

I also frequently hear that "insurance disallowed"
statement. If insurance was "disallowed" for a NEC safety or
rule violation, very few claims would ever be paid. In my
entire life I can't recall having a claim denied because of
something like this. I would bet well over half of  Ham
stations lack a proper entrance or station ground bonded to
the mains ground, but I don't recall ever knowing of a claim
disallowed for that gross error.

73 Tom
===========================
Tom, and all:

Have to agree with you.
Hundreds of feet of electrical ground wire from antennas?  Not even 
sure that would work for lightening.
I have a ground rod at the base of my 600m inverted-L antenna (RF 
ground) and the 2-ft wide x 50-foot to 70-foot long radials are 
connected there.
Z = 18 - j681.5
Rad = 0.8 ohms so most is ground loss

I have a 120-foot run of 1-5/8 inch LDF7-50A Heliax that is grounded 
at the base of the tower and at the cable entrance to the shack.  The 
cable entrance is a 12x 16 inch aluminum plate that has 26 coaxial 
feed thru connectors (I have over 17 antennas).  The mains 
(electrical meter box) is grounded on the other side of the house so 
to bond them would take 50+28+50= 128 feet of ground wire.  That 
might be effective if It was #6 or larger.  I got better places to spend money.

My Beverage antenna has two ground rods at either end but is 150-feet 
from the cable entrance.  I have begun using ferrite RF Chokes a lot 
on my coax with excellent results.  They are not expensive and nicer 
to look at then a big coil of coax.


73, Ed - KL7UW, WD2XSH/45
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