[TowerTalk] Single Point Grounding question

[Roger (K8RI)]

K1TTT 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.
>>     
>
>
> How long are the jumpers from the bulkhead to the switch? 
About 8'
>   Could you tell
> where the arc initiated on the coax,
 From the shell of the disconnected PL-259 to the frame of the Alpha 
Delta coax switch....which also ties to that same grounded bulkhead
>  the connector shell or the center
> conductor??
>
>   
It almost had to be the shell as the Polyphaser was OK.

73

Roger (K8RI)
>
> David Robbins K1TTT
> e-mail: mailto:k1ttt at arrl.net
> web: http://www.k1ttt.net
> AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
>
>
>
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