Subject: Q: ARCING BETWEEN ELEC. CONTACTS & HOUSING

From: [email-masked] (BJ)
Date: Wed, 24 May 1995 23:31:33 +1100

24 MAY 95, 23:20 PDT

I am interested in getting advice or comments on the following engineering
problem.  Two electrical contacts are housed in a stainless steel
housing.  In some cases the housing is grounded and the contacts are at
something like +/- 150 volts.  After laser welding the housing shut it is
back-filled with Nitrogen & Helium trace (for leak detection).  In field
service, arcing occurs between the contacts and the housing.

Is there anything thing to consider that would suggest a different
back-fill gas if we wanted to stay with the SS?

Is it possible that the back-fill gas is getting ionized before or during
the back-fill process?

If anyone has had this problem and solved it we would be interested in
hearing your approach.

R. K.

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From: [email-masked] (HARDBALLER)
Date: 29 May 1995 17:43:46 -0400

Regarding your arcing problem, it would be clear to anyone who has done
any TIG welding what your problem is...unfortunately you didn't mention
what the distance between contacts is or whether you were operating ac or
dc current. In any case, it would appear that you have created a nearly
optimal environment to strike an arc,ie:  a (grounded?) conductive
enclosure filled with inert gas, containing exposed contacts operating at
sufficient voltage to strike an arc.  Under these conditions, I would
probably recommend in insulating material be positioned between the
contacts and between the contacts and the housing.  Silicone rubber would
be good or Nomex or possibly even Mica.  This way you can retain your
inert gas fill.  Good Luck.