[TowerTalk] SPG & Service Entrance Grounds.

[Julio Peralta]

How about a "local area single point ground"?

Julio, W4HY

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Roger (K8RI)
Sent: Thursday, September 13, 2007 4:48 PM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] SPG & Service Entrance Grounds.

I know we are beating this to death, but it is a topic that I think
deserves 
the attention.

No matter which way we go with alternatives we run into conflicts or the

actual term Single Point Ground ( SPG)  which requires a definition.

>>
>>Sometimes these alternatives are all that can be done at a particular
site
>>but they are not "single point ground systems" and should not be
called
>>such.

Agreed.

>
> ------------ REPLY FOLLOWS ------------
>
> My point exactly. In English, the word "single" has a specific
> meaning. If you have more than one ground point but you use the word

Here we have to be careful and remember the ground point is where the 
equipment ties into the ground system.

> "single", you are confusing the issue. There is nothing wrong with
> saying "Double Point Ground" or "Multiple Point Ground" or "Multiple
> Ground Points".

Except they do not convey the concept of a single point ground If that
is 
the goal.
First we need to think of "ground" as a "system" of wire and ground
rods. 
Unless it's the only ground rod, each ground rod doens't represent a
"ground 
point" as it is no more than an *extension* of a grounding network or 
system. By themselves, the service entrance, phone line(s), antennas,
and 
cable each represent a ground point where they enter the home which in
this 
case would be 4 ground points.  If allowed to remain seperate the
equipment 
tied to them can rise to different potentials (sometimes drastically 
different) from a nearby or direct lightning strike.  Generally, codes 
require all of these be tied together to form one single system. Even
metal 
water and gas lines are required to be tied into this system.

My satellite receivers have a ground to the AC mains, but they also have
a 
telephone line, antenna(2), and cable connection.  This is not a good
thing 
as it is one of the reasons for damage caused by nearby lightning
strikes. 
In those satellite receivers I'd have 4 systems coming in that are
seperated 
by a lot of fragile and expensive components.   From an engineering
approach 
one point on this system needs to be selected to which all equipment
grounds 
are tied. This single point then becomes the "Single Grounding Point"
for 
all of the electrical equipment. Hence the term, Single Point Ground.
The 
problem with this term has been well covered, but any of the proposed 
alternatives mean something else. OTOH if a station, or home doesn't
have a 
SPG then call it what it is.

A home, or shop my have multiple grounds such as the electrical, phone, 
antennas, and cable.  These grounds all need to be tied together to
create 
"one ground system".  If they all tie together at one point such as the 
bulkhead and all equipment is grounded to that point then each, or
rather 
all the equipment sees the entire ground system as one single point. 
Refering to more than one ground point could be interpeted as each piece
of 
equipment such as the electrical mains, telephone,  antennas, and radio
as 
having their own indivicual grounds and that is we are tying to avoid. 
"Common point ground" also has a problem as there is a point where an 
electrical system "common" is grounded.

>
> Please call it what it is.

That's the problem. Finding a term that really means the grounds for 
everything are tied to one single point which is the goal.


73

Roger (K8RI)

>
> Bill W6WRT
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