Problem with 10ee DC panel - tripping RCD

Over the past week I have had my lathe trip the RCD in the workshop feed panel, always when the machine has warmed up and sometimes apparently triggered by parting-off chatter though whether it's the load or the chatter that's the cause I could not say. It's been giving me a headache because it's a fault that will right itself when I am looking for the cause, or when I've got fed up scrabbling about in the dark for the reset switch and left it until morning.

When it does trip the RCD if I reset it then it pushing the green start button will knock it off again right away.

Last night it went off again, only this time the fault has remained this morning with the machine stone cold. I've worked my way through the machine with a meter until I think I have found the source of the fault. I had 600ohms between the (MG) end of the E1 wire and the earthed chassis. I opened the DC panel up to trace the other end of the E1 wire (which should be the DC- supply to the panel/field) and the problem went away i.e I no longer have 600 ohms from E1 to earth.

(Worth noting that there is no MG in my machine. Field/panel voltage is provided by a variac and capacitor and armature power by a 1Q DC drive. The DC panel is however all-original and uses the original features including the ohmite for field weakening. Only the 115v feed to it is changed.)

I've studied the panel and all the internal connections and I can't find any obvious fault. I suspect that I have a condenser failing since looking at the diagram it seems that E1 from the MG is connected to K1-2 terminal then goes through the overload to the condenser and nowhere else, but my electrical knowledge is weak and I want to put it out here for opinions/suggestions.

Any assistance would be greatly appreciated.

I assume that an RCD is what we call a circuit breaker on this side of the pond? What amperage rating is the breaker?

I think I would start by temporarily removing the DC control panel from the system. If the problem goes away, then continue to look at the DC panel as the culprit.

Cal

I bought my 10EE over 25 years ago...

It drove me nucking futs with electrical issues. Paid a good electrician big bucks to keep it repaired. The joke about needing a EE (electrical engineer) to run one was true.

About 15 years ago, I ripped it all out and installed a VFD and 3 phase motor. never had an issue since.

Anyway, my suggestion would be to consider this route if you do not quickly resolve the issue.

Thank you all for the replies.

Cal: RCD= residual current device. It detects earth leakage and throws the breaker out. Usually set to 30ma but can be anything.

Disconnecting the panel supply stopped the fault. An ohm meter from the panel negative feed (labelled E1 at the MG junction box end) to earth was showing about 600ohm. I took the cover off the panel and also released it to swing out to inspect it - problem went away. E1 now shows no circuit to earth and the machine works normally.

Bill - good idea if the panel faults again I will first get my air line and poke it round the corner and give it all a good blast.

Karl_T - I've always said that if the panel dies I will do the VFD conversion. I love that motor though so it might end up being a 4Q drive conversion. Time will tell.

That sounds like what we call a GFCI = Ground Fault Circuit Interrupter.

10EE DC panels are very robust and a usually a lot easier to repair than doing a proper VFD conversion.

Cal