Glad you put it that way, Jim. I think the term "single point" has confused a
lot of hams. The essential thing, as you say, is to make sure all the grounds
are bonded together by the shortest practical path.
I think what most people like to call a "single point" ground is the station
ground on the outside of the house to which all the station equipment, cables
and tower ground system are bonded. It's usually convenient and practical to
bond all these things together in one place as they enter the house. But that
ground point must never stand alone -- it must be bonded to any and all of the
other ground systems you have.
There's no reason why a station can't have more than one grounding point for
equipment chassis and cable grounding. In fact, many do: one might be a set of
ground rods tied to a common point at the tower for cables, switches, lightning
suppressors, metal equipment cabinet, the tower itself, the Ufer ground, etc.,
and another set of ground rods at the house tied to a common point for chassis
grounding, cable grounding, lightning suppressors, switches, equipment
cabinets, etc. But the two ground systems must be bonded together, and they
must be bonded to all the other ground systems in your house: AC, telco, cable,
satellite, etc., etc.
Some grounding decisions are not straightforward. For example, my AC and telco
services are on one side of the house and the station "single-point" ground is
on the other side of the house. It would have taken 150 feet of low-inductance
wire and at least 10 8-foot ground rods and Cadweld shots to connect the ground
systems outside the house. So I decided to bond them together inside the house,
using about 25 feet of 1/0 wire. Not the recommended way to do it, but it my
opinion a better way to ensure that the ground systems are at the same
potential.
Another example is bonding the tower ground to the single-point ground at the
house. My first tower farm is 265' from the house. Being new to tower
construction, I laid 265 feet of 1/0 ground wire in the trench running between
the two locations in order to bond the ground systems. This was not cheap, to
say the least (though it was before the big run up in copper prices.) Later, I
read an article by Polyphaser that said if the ground systems are more than 75'
apart it does no good to bond them -- the wire inductance will be too high to
make an effective connection. With this in mind, when I installed my second
tower system in a different location 220' from the house, I did not run a
separate ground wire. The Polyphaser argument made sense to me. Also, there are
two runs of 1-5/8" hardline in the trench, and the gigantic copper shields on
those babies surely provide a lower inductance path between the tower and house
than a 1/0 wire would -- if, in fact, any wire has low enough inductance at
that length to be effective.
73, Dick WC1M
> -----Original Message-----
> From: Jim Brown [mailto:jim@audiosystemsgroup.com]
> Sent: Monday, January 21, 2013 7:24 PM
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] bonding to AC power box or inside fuse panel?
>
> On 1/21/2013 2:51 PM, Jeff Blaine wrote:
> > What’s the best way to effect a single point ground in this
> combination?
>
> Stop worrying about "single point" and simply bond EVERYTHING together
> by the shortest practical path. In the power entrance panel for ANY
> premises, earth must be bonded to the enclosure itself, and there must
> be a bond between neutral and that enclosure. By EVERYTHING I mean
> everything in your home that is grounded, including CATV entrance, Telco
> entrance, power entrance, your antenna entrance, your shack operating
> desk, structural steel if there is any, cold water (if it's metallic),
> lightning protection, etc.
>
> In general, you can have as many earth connections as you like, they can
> be anywhere you like, but they MUST all be bonded together. Anything NOT
> bonded is unsafe.
>
> 73,
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