Clearly, I'm in good company, then!

But if you want another laugh - I bolted the ET6 in place, connected power and ethernet connections only so I could start on the config process. Plug into extension lead, turn on front panel switch. Nothing, Ah, internal MCB is off. Flick lever. Bang, flash, MCB tripped. Shout from wife in sitting room - "the power's gone off!". Interestingly, took out the 10A MCB in the cabinet, 32A MCB in the consumer unit, plus 100A RCD covering all house rings. 13A fuses in extension lead and cabinet mains lead still OK. Sums up my approach to fuses - they really are the last resort when all else has failed!

Cause was one of those little thing that could happen to anyone. After isolating cable between MCB and mains switch (which is after MCB), the cable was still shorted to earth. I had had to remove the nuts securing the mounting panel in the cabinet and on replacing one last night, I managed to catch the mains cable under it. The nut has a built-in shakeproof washer which comprehensively mashed the insulation.

Still, the board is now talking to my Win10 laptop first time, and I'm starting "ports and pins" configuration via the MyCNC user interface..