[TowerTalk] Back of desk grounding buss

Keith Dutson kdutson at sbcglobal.net
Sat Mar 22 15:40:44 EDT 2014

I have two fairly large stations, so purchased two Harger bars.  They were
the only commercially available grounding system that I could find.  I did
not want to build something.  The Harger kit came with bolts, screws and
grounding straps.  So, while a waste of money for some, it was the best
solution for me.

One may get an understanding of lightning protection from the documents
published by Polyphaser.  I have read most of these, plus gained a lot of
insight from other multi-station owners.

73, Keith NM5G

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Ian
Sent: Saturday, March 22, 2014 4:41 AM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Back of desk grounding buss

>> Get the Harger ground bar.
>Big waste of money.
>73, Jim K9YC

Agreed. The topic here is "back of the desk grounding", and in that location
a massive copper busbar is a big waste of money. Worse still, it may
indicate a dangerous lack of understanding.

The place for massive copper conductors is <outside> of the building and at
the common entrance point. These conductors need to be large enough to
handle huge lightning-induced surges and divert them away from the shack.
Once again: the aim is to keep large surge currents <out> of the shack
entirely, or at least to reduce them to some low residual level. 

By the time those residual surges reach the back of the desk, there should
be no further need for massive copper conductors. The bonding strip along
the back of the desk is there for a different purpose: to provide a
low-impedance "local ground" reference for all the equipment lined up along
the desk. The aim is to provide a low impedance at all frequencies from DC
through 50/60Hz up to RF, and when you run the numbers the main requirement
is for low inductance, which is best achieved by a wide flat strip conductor
or a large-diameter pipe. Aim for the low inductance, and you will almost
always find that the conductor cross-section is large enough for 50/60Hz
safety and hum suppression as well.

One more time: the main purpose of the strip along the back of the desk is
to ensure that all the equipment metalwork is closely connected <together>
at all frequencies from DC to RF. The best term for this is "BONDING". 

(Thoughtful authors try to avoid  calling it "grounding" or "earthing"
because a connection to the Mother Planet is not the main aim. You should
connect the bonding strip to a mains safety ground as well, but that was not
your main reason for having the bonding strip.)

73 from Ian GM3SEK


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