Roger:
I wonder if something like the Alpha Delta Transi-Trap Surge Protector
installed at the base of the tower would have prevented the flash over?
That's what I have but not up at the shack entry.
73
Bill Harris w7kxb
--------------------------------------------------
From: "Roger (K8RI)" <K8RI-on-TowerTalk@tm.net>
Sent: Thursday, September 03, 2009 4:30 PM
To: "K1TTT" <K1TTT@ARRL.NET>
Cc: "'TowerTalk'" <towertalk@contesting.com>
Subject: Re: [TowerTalk] Single Point Grounding question
>
>
> 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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>>
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