Ok.... I disconnected the Spindle power cable braided sleeve so it is now fully insulated at both ends, and so is not physically touching the metal spindle plug either.

With the spindle turned on at 18,000 rpm, I have a 40 Volt ac signal generated, between the Spindle/Machine, and the spindle power cords' Braided Sleeve, at 9,000 hz. The machine ran without issue.

So - should I run an earth from the braided sleeve to house . power inverter earth at one end.... I don't see how this would dissipate electricity though as it's an AC signal effectively being generated by EMI.

2. I will probably run another earth wire back from the spindle to the House earth now - to stop electric shocks in the case of other failures.....

If I have the AC leaking braided sleeve earthed with the inverter / house earth, and also conect an earth from the spindle to the inverter / house earth, I could be back at square 1 as the spindle could get some of the AC?