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From: email@example.com (Bob Wilson)
Subject: Re: Best insulator?
Date: Mon, 09 Sep 2002 05:38:51 -0000
Organization: Your Organization
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In article , firstname.lastname@example.org
>I need to apply 500v to one lead of a twisted pair, relative to the other.
>The two leads are connected to two connectors mounted on a Tufnel base that
>I can't change. At the moment, I'm using Nylon 6 stand-offs from the base
>the connectors. The assembly leaks 1nA which is greater than the 0.01nA
>leakage that I require. A PTFE washer might do the trick.
>"Ian Stirling" wrote in message
>> sally wrote:
>> > Thanks for the info. Are mylar stand-offs, screws, washers etc
>> > and how easy is mylar to drill and machine?
>> > Sally
>> I don't think mylar screws are readily available.
>> Nylon, and to some extent PTFE are.
>> What do you want to insulate, and how much?
>> There may be other solutions.
Nylon is an extremely bad choice. In fact it is the worst choice possible.
It has the highest moisture absorption of any plastic (by a very large
margin). So much so, that it changes dimension as humidity changes. There
are no screws or other similar hardware available that are made from "Mylar"
(polyester) because Mylar is a material available only in film/sheet format.
PTFE (teflon) is a good choice for low leakage applications because it has a
somewhat better dielectric withstand capability, but in particular it has
essentially zero water absorption and more importantly is hydrophobic. It's
only problem is that it is mechanically very weak. Screws made from PTFE
stretch like crazy.
Another good choice is Rexolite (chemically pure polystyrene). Good
electrical propeties, but mechanically it is the opposite of PTFE; it is
hard and brittle. But at least it does not exhibit physical creep under
tension or compression.
Acetal (AKA "Delrin") hardware may be a good compromise.
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