# [TowerTalk] PL-259 Voltage Breakdown

Tue Dec 11 14:21:21 EST 2007

```Breakdown on a connector is going to be most likely due to creep along the surface.  The usual rule of thumb is that the breakdown along a surface is 1/3 that of the distance in free air (hence the ribs and notches in HV insulators).  Looking at
http://www.rfconnector.com/pdf/cat-uhf-series.pdf

It looks like the distance from outer shell to center conductor on the PL-259 [ (A-B)/2 in the figure) is 4mm.

For the SO-239, it's even less distance, because the "socket" has to be larger diameter than the pin from the PL259.

Let's say 3mm. using the 1/3 rule of thumb, we need the breakdown for a 1mm air gap:  Breakdown for air is 25kV/cm, so, roughly 2.5 kV.

There are lots of sharp edges in the connector, which reduces the breakdown voltage, etc.  The 500V in the Amphenol spec referred to below is probably a reasonable number (500Vrms, that is.. 700V pk) with 2:1 margin. The link above cites 1500Vrms as the dielectric withstand voltage (i.e. plunge the connector in oil and it should take 1500Vrms without the dielectric failing)

As others have noted, this is a dicey area in general.. there's a lot of factors that affect HV breakdown, and the UHF connector is certainly not designed for HV.  If you need a connector that takes HV, there's a LOT of better choices... Modified UHF connectors are widely used as the mechanical basis, but you drill out the insulator and extend the dielectric of the coax a few inches and put a banana plug on the end.

For real connectors (as opposed to something you make).. SHV, HN, HC, etc. are all high voltage versions of standard RF connectors (BNC, N, and C, respectively)

For DC, I've built lots of HV connectors using PVC pipe and banana plugs/jacks. Easy to arrange long creepage distances, secure connection, and "no finger touch" (think of scaling up the jacks and plugs on modern multmeters.)

Jim, W6RMK

-----Original Message-----
>From: Steve Katz <stevek at jmr.com>
>Sent: Dec 11, 2007 10:41 AM
>To: "Roger (K8RI)" <K8RI-on-TowerTalk at tm.net>, TOWERTALK at contesting.com
>Subject: Re: [TowerTalk] PL-259 Voltage Breakdown
>
>I've had PL-259s fail hipot (set to 3mA trip point) at way under 6 kV.
>It depends on the air around them.  Air's a great dielectric when it's
>dry (0% humidity) and a lousy one when it's wet (100% humidity).
>Without a controlled environment, you can't define the BV of this kind
>of part.

>Subject: Re: [TowerTalk] PL-259 Voltage Breakdown
>
>
>>Did you see this on Amphenol's website? I didn't search other mfgrs.
>500 V breakdown, or working is unrealistic for a good connector. IIRC
>that
>is about what teflon is rated per mil. Even air, which you have between
>the
>conductors at the interface between connectors would be much higher than
>500
>V .
>
>I've run as high as 6KV on them.  Hy-pot one and it'll probably be good
>for
>about 12KV, but I'd not want to run one that high.
>
>Roger (K8RI)
>
>
>>Ron
>>N5QQ
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```