Bill Harris wrote:
> 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.
I doubt it as the shield for the coax cables are grounded side by side
at the tower and at the bulkhead where they enter the house. The two
leads that arced over are about 8' long and are just a continuation of
those same coax cables.
> 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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>>
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>
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