Hi Bill -

One of the results of my transformer testing using the prototype power
can has been the discovery that the Fluorinert will slowly pick up
excess o-ring lube around the can and connector seals.  The lube winds
up being concentrated in the transformer tank since the only exit from
there is by evaporation (it's kind of a miniature still...).  Since
there is critical high voltage insulation in that tank, I have some
concerns that the o-ring lube that we use in this application have
reasonable dielectric qualities.  Silicone grease, e.g. Dow Corning 4 or
(probably) High Vacuum Grease, seems like a safe choice from an
electrical standpoint.  Absent solid data to the contrary I'd have
worries about any metal-soap based grease or even about Aqua Lube for
that matter (to say nothing of dealing with a transformer tank coated
with a thin layer of Aqua-Lube...).

I just disassemled the DG OBrien connector from the AC Can endbell (so
we can replace the wires on it) and noticed that it appeared to have
been assembled using mostly silicone grease (not sure exactly what
kind).  The grease appeared to be in good condition and I saw zero sign
of deterioration or corrosion (this assembly was submerged during prototype
testing and also went thru high temperature thermal testing on my
bench).  With that as a data point I'd like to propose that we specify
only silicone grease on the AC Can o-rings, and as little of *that* as
is practical.  

However, "keeping the water out" ie having the o-rings work reliably, is
even more important.  So if you need to specify some other kind of lube
for whatever reason, go ahead.  Also requiring silicone on the AC Can is
a minor maintenance and logistical hassle, for which I apologize, but
the alternate seems worse to me.

Anyway let me know what you think about this.

thanks,
Ed