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
