Sprague 2X.1-1000 filter capacitors and 854-B power control assembly

Tom Hunter ccth6600 at gmail.com
Mon May 3 05:45:27 CDT 2021

 Unfortunately once again I am having trouble with Sprague 2X.1-1000 filter
capacitors. The two filter caps on a Lab-8/e rack's 854-B power control
assembly appear to occasionally leak to ground more than the 30 mA
tolerated by my RCD. Mostly it trips the RCD when I power off the system,
but sometimes it even trips the RCD with the system powered off. One of the
two filter caps is permanently connected across mains power and earth
coming from the cable (i.e. it is before the power switch).

The exact same filter caps were also used inside the LAB-8/e computer’s
power supply. Early on I replaced these with a small PCB with a bunch of
male spade connectors and two Y class safety caps. The PCB was designed to
replace two of the Sprague filter caps in the side-by-side configuration
used inside the LAB-8/e’s power supply where it is also hidden from view.
The PCB was designed by Malcolm Macleod in Melbourne/Australia who hit the
same problem. I got the PCB manufactured in China from his design.

The 854-B power control assembly has the two Sprague filter caps sitting on
either end of the assembly – far from each other. Also the can of the
capacitors is exposed at the back and clearly visible so even a newly
designed PCB with a single set of safety caps wouldn’t look great and also
wouldn’t be stable because there are only two mounting holes.

I cannot think of a neat solution to resolve this.

I could try to find an electrician willing to wire me a non-RCD protected
socket into my study, but I can’t quite warm to that idea. The RCD is an
important safety feature. By law now all houses are required to have their
AC wiring protected by 30 mA RCD circuit breakers so I likely would have to
do this myself.

The other option would be to make or buy two terminal blocks with male
spade connectors and connect the female spade connectors to those rather
than the Sprague connectors. I could then also wire in the 2 Y class safety
caps or even forego the filtering. It would mean drilling new holes into
the power control assembly.

Chuck(G) in the vcfed DEC forum suggested pulling apart the old "bathtub"
capacitors and replacing their guts with modern safety caps. The caps
contain toxic and carcinogenic PCBs so I am less than enthusiastic about
that idea. The capacitor's metal can is soldered together so trying to
desolder it would heat the mineral oil containing the PCBs which would make
them even more harmful.

There is no point in trying to hunt for “new” Sprague 2X.1-1000 because
they would all be ancient and have the same leakage problem.

Any thoughts, ideas or suggestions?

Best regards
Tom Hunter

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