Update... worked for a long long time running the lathe and coolant pump in parallel (machining stainless). Long enough for the cast iron headstock to warm up a bit.
Failed after about 3 minutes on the router, but this time only the VFD, circuit breaker didn't trip. I just got the 'ELuS' error... I've only had an error before on the VFD when I've been getting a bit carried away on the lathe and overloaded it (so not often).

I'm going to buy another VFD now as I could do with having two anyway as then I can run the lathe and router at the same time. I think I'll get a 3kW one as the lathe plus pump is borderline on the 2.2kW. It will help diagnose the problem, though I hope to have sorted it by then.

Quote Originally Posted by russell View Post
If you can, borrow an earth continuity tester and make sure the resistance between parts is less than 0.1 ohm.
Considering they wouldn't even let me borrow a soldering iron for a couple of hours from Uni, I think there's not much hope of that. Unless there's somewhere else...


Quote Originally Posted by russell View Post
Although a potentially unsafe practice this shows no problem. ... measuring a current of only 18 [FONT=Times New Roman, serif]μA.
Yes DVM, so that's true. I did consider putting a high-ish value resistor from the frame to earth with that test and measuring the voltage across it to see if it will sustain a higher current. Is it worth it?

Quote Originally Posted by russell View Post
Try measuring the leakage current of the VFD on its own. If that is the problem connect it via a separate, lower sensitivity RCD but make sure your earth bonding is good!
I will try that again next weekend. This weekend I only managed to cut one part on the router, and some bits on the lathe