Blue Elephant is biting me

Hi
Looking for some advice please

I'm having trouble with my first CNC. She's a 4 axis 4 spindle Blue Elephant, purchased second hand. It's 3 phase no neutral.
Problem I'm having is:
there is 70 volts on the floating earth relative to true earth. First noticed after I got a tingle on the cabinet while initial testing.
I've been through the machine with a standard multimeter looking for anomalies, with zero answers.
Purchased a megger and tested at 240v. Nothing showing up! Is it lunacy to test at 500v?

I've received quotes from repair specialists that would make you weep! Hoping to crack it myself. I'm just a hobbyist you see.

Ideally someone has knowledge of the likely culprit, that would be a massive help!

Basic component list:

6x H2-2206 Hybrid Easy Servo Drive
6x Leadshine 863HSM80H-E1 Servo Motor
4x Fu Ling Inverter DZB200B002.2L2DK 2.2kw 220v
4x 2.2kw chinese water cooled spindles

Thank you in advance