There will always be a potential difference between them during a lightning
stroke, you can't prevent that. The concept of a spg is to protect
equipment in a building. All the wires coming in through the spg are
connected together so they are all at the same potential so there should be
no chance for arcing and sparking inside the building.
To confuse the issue a bit, a single installation may have multiple 'single
point grounds'. Consider the case of a house with a separate garage that
has the radio shack in it. There would most likely be a spg for the garage
so all the equipment in there is protected... and a separate one for the
house where the power, phone, catv, satellite tv, etc comes in to protect
all that stuff. Thinking this way you could also create an spg for the
tower as a structure, bonding all cables at the bottom of the tower with
proper arresters, etc to protect everything on the tower... but this would
not substitute for an spg on the house.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: Bill Harris [mailto:w7kxb@msn.com]
> Sent: Thursday, September 03, 2009 19:24
> To: TowerTalk
> Subject: [TowerTalk] Single Point Grounding question
>
> Hello radio fans:
> My question is:
> For lightning protection, the tower base is delta grounded. Coax, shield
> grounded at the antenna therefore, wouldn't the best place for SPG be at
> the tower base rather than the shack entry ?
> I'm concerned about about having difference in potential between two
> grounds. Your input is most appreciated.
> Carry-on
> BillHarris w7kxb
>
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