Hi Steve, I guess they underspec. the cable intentionally to not get a
bunch of lawyers on their back in case it arcs over and causes damage.
However, the time in service may also be a factor since micro holes
can form over time in insulation materials and the effective isolation
may decrease. Most cable suppliers don't even have a max DC voltage
stated in their specs. I suspect that HV-use is not a big market for
the suppliers of coax and they probably don't put down a lot of
resources in testing and speccing it.
I have checked with Pasternack, and they can deliver a crimp version
of the SHV for RG213 with solid core. This should withstand very high
voltages. The challenge with RG213 is that it is quite stiff so that
in case decide to I use 213, I will design a cable and plug attachment
post in the back of the amp so that there will be no adverse bending
of the connector.
LB3HC
Message: 4
Date: Thu, 16 Sep 2010 08:58:19 +0100
From: Steve Thompson <g8gsq@f2s.com>
Subject: Re: [Amps] SHV / proper cable for DC energy transfer
To: amps@contesting.com
Message-ID: <4C91CE1B.3010204@f2s.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
I haven't tried to find exact details of anyone's test process but
I suspect that the cable manufacturers specify the breakdown
voltage with a flat cut end on the cable, or with the cable
prepared as it would be in a typical connector (BNC, for example).
The dielectric strength of polyethylene is around 20kV/mm. When
there is sufficient path length to prevent arcing on the cut ends,
I can't get breakdown in good quality RG58 at 16kV (the limit of
my hipot tester). I'd say that breakdown in the cable itself is
not an issue in your situation.
Steve
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