Roger,
Do you have arrestors on the bulkhead entrance to the house (center
conductor protection), or just the outer conductor grounded?
Chris
KF7P
On Sep 3, 2009, at 17:30 , Roger (K8RI) wrote:
K1TTT wrote:
> 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.
>
Even that only sota, kinda, almost works. All of my cables come in
through a bulkhead. The coax cable shields are grounded at the base of
the tower AND they are grounded at the bulkhead along with the other
coax cables, rotator cables, remote antenna switch cables, where they
come in the house. I've mentioned this before, but two of the cables are
from the 144 and 440 arrays. Both have pigtails that run from the
bulkhead to the antenna selector switch. I had one of them disconnected
and laying on the desk about 8" to 10" from the switch. Lightning hit
the tower and there was a tremendous flash from the coax laying on the
desk to the selector switch. Yet both cables are the same length and run
to the same grounding bulkhead. Why the flash-over? It sounded like
some one fired a 12 gage here in the den. BTW both antennas are at DC
ground.
73
Roger (K8RI)
> 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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>
>
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