[time-nuts] Galvanic decoupling of GPS antenna

[Robert Benward]

The jacket might be rated for it, but if it's a commercial operation, it's 
against code to route it around without protection.  This would also apply 
to your house, you can't run Romex vertically or horizontally against walls 
where a human might crash into it, or damage it. The fear being bumping into 
the exposed Romex with sharp metal object (tool) and cutting the insulation 
which would present an electrocution hazard.  Overhead in the ceiling joists 
is OK, but lower that head height, NG.  If it's against the wall, it should 
be conduit, if it's floating like a connection to your boiler, then BX is 
acceptable.

Bob




----- Original Message ----- 
From: "jimlux" <jimlux at earthlink.net>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Friday, June 18, 2010 1:46 PM
Subject: Re: [time-nuts] Galvanic decoupling of GPS antenna


> Robert Benward wrote:
>> Rated for 1400V from CENTER conductor to shield, not shield to the
>> outside. If you choose to use RG-58 with 250V on the shield then you
>> will need to put the entire cable inside conduit.  It is not acceptable
>> to have any type of exposed mounting.
>>
>> Bob
>>
>
> Yeah... I've been looking for the jacket rating...  As a practical
> matter, I've used solid dielectric RG-58 (both A and C flavors) to carry
> 10kVrms AC (neon sign transformer type voltages).  Usually, you don't
> get breakdown between center/shield.
>
> However, considering that ordinary PVC insulated hookup wire is rated at
> 300V, I suspect it's ok.
>
> Obviously, we're talking a transient here.. if you're floating the
> shield at 200V above surrounding objects/ground, a better solution is
> called for.
>
>
> Interestingly, looking at MIL-C-17 (which covers coax)
>
> There are several requirements for RG-58 (MIL-C-17-28)
> Spark test: 5000V rms +10%/-0%
> Voltage Withstanding: 5000Vrms +10%/-0%
> Corona extinction voltage 1900Vrms minimum
>
> Then, looking at the test procedures in Sec 4.8 of MIL-C-17G
>
> Spark test (4.8.3) A test voltage at a frequency...shall be applied
> between the outermost braid or shield and the outer surface of the jacket.
>
> Voltage withstanding (4.8.4) (a) For coaxial cables. The test voltage
> shall be applied between the inner and the outer conductor, with the
> outer conductor grounded.
>
>
> Overall.. MIL-C-17 is a great reference on how to test coax (or to ask
> your coax supplier about how they test...)
>
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