Survivor!

It's only doing it to annoy you. Make sure it is run well within its ratings and put it on a board that has to be buried several layers deep in some complicated equipment and is rivetted in place. It will fail in no time at all and probably take several other valuable components with it.

Lots of parts can be forced way past their rated maximums and suffer internal damage that won't then show for a period of time in normal use.

That's why we have fuses, TSVs, MOVs, etc to help protect against spikes and their aftereffects.

The only way to find what happened to the cap is to take the capacitor apart and study the elements under a microscope for punctures and do a chemical analysis on the electrolyte.

This is just A-Waste-Of-Time experiment and I can't believe I am commenting on it...

John :-#(#

Obviously it was able to survive the overcurrent situation for long enough to blow the fuse in the variac. Since, as usual, you've left off all useful information (i.e., make and model of cap) we can't comment any further.

The fuse also did it's job, which is to protect downstream components from overcurrent situations by blowing before the downstream items themselves blow up.

Fuses are really to protect the power source. They do usually protect the wiring in the down stream device from a total meltdown.

LOL! Yeah, you got that 100% right I reckon, Liz. I realise I've probably curtailed the service life of this cap by some considerable amount, but nevertheless it's still remarkable it wasn't totally destroyed. Vintage NOS parts for you: none of your Chinese rubbish. :-)

Yeah, well you did. Incidentally, why are you Canadians so desperately

More importantly the fuse protected the variac. They are very intolerant of even quite modest overloads. John

I have successfully protected one with a thermal cutout which has low thermal inertia and has always operated before any damage can occur. It is in a bench power supply that is often used to test faulty equipment, so fuses would not give a quick and easy reset facility.

It suffered a lot of nuisance tripping on loads well below the variac's rating until I realised that the isolation transformer, which it fed, was drawing a large magnetising current. I have corrected the power factor of the transformer with a capacitor and the nuisance tripping has now ceased.