Electrical, Help me Guys, Figure Out Chain of Events

You seem to have a neutral to earth leakage via carbonised nylon in the connector that has failed. Notice the charred nylon tracking from the blue wire to the screw that retains the connector. I would imagine the fault started as you say by a lose terminal, and the RCD tripped probably due to the tracking.

I would replace the connector block and see if the tripping goes away, otherwise there is a useful guide to RCDs and tripping here :

AWEM

It is likely that the either the screw walked loose as a result of repeated heating and cooling cycles or that the wires relaxed a bit from the same cause. These are problems with chocolate block connections that are run warm or with reasonable currents. After replacing it, run things for a while (week/month/6 months depending on use), then re-tighten the connections.

The RCD may have been sensitised at some point, or there may still be earth leakage from somewhere else. Is the converter isolated from the mains by pulling out a plug or a double pole switch? If not, then the neutral is probably still leaking to ground and using up most of the leakage current that the RCD is designed to sense, thus making it respond to the slightest bit extra from other things. Motors and immersion heaters often have a bit of a leak when they first get going :-)

Not unless fixing the converter doesn't cure the problem.

Change the terminal block as a matter of course. Then see if the spurious trips have gone away. Or, as a short term expedient:-

1) Tighten the chocolate block contact screws if they aren't completely buggered. 2) Unscrew the block from the autotransformer. 3) Cut the three sections apart. 4) Tape the individual sections up. 5) Rest them on the transformer on a bit of wood to stop the tape from getting too hot. 6) See if the problem has gone away.

regards Mark Rand RTFM

HI MARK

The converter was completely disconnected from the mains when the compressor was tried out. ...had to, as it was on brackets mounted high up in the workshop ...out of the dust and out of the way of damage ...so to take it down, involved disconnecting it completely.

I would add, after a long period of operation there was always a smell of ozone around this converter ...even from new ...so I think that arcing has been going on for a long time........so I think screws were loose from new.

And when changing speeds on the lathe mid-flight ....the converter would always stutter ..........I thought this was the old contactors in the lathe...it's done that from new as well.

RCD has tripped probably over 200 times in its life mainly due to a couple of rings "out" on my cooker that I keep forgetting about ... would the number of trips and faults over a period of time wear it out ..and now make it overly sensative....it's too much of a co- incidence that the comp and the water heater now trip it out ...me thinks.

The workshop has its own consumer unit and 30 milliamp RCD that never trips .......always trips the house one up-stream.

To test the new chocolate block six months into the future, will... like today, involve quite a bit of work ... and calling a friend to help me get the thing down .weighs over 100 lbs. The cover can only be taken off on the floor ...

Do you think a bit of blue locktite on the block screws would maybe help ...me fit and forget.

Yes... I will try to insulate the new block from any heat.

all the best.....mark

I can't advise regarding the RCD. You have been 'using' it quite a lot but I would of thought it should stand such use.

When you replace the terminal block, consider getting one with a bigger wire capacity. When fitting, strip more insulation off the wires such that all wires pass under both screws and do both up tight. I don't think loctite will be much use if the screws are done up properly in the first place.

Good Luck

Bob