Blue Elephant is biting me

[jaypee89]

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

[Clive S]

Do you have 3ph in your shop ?

[m_c]

If things aren't earthed properly, then the various filtering capacitors in the drives/PSUs can cause floating voltages.

So I'd want to know why you have a "floating earth"?
All metal parts of the cabinet/machine should be earthed.
If they're not, then I'd be looking to see why they aren't.
It could be that somebody has disconnected them as a bodge to stop an RCD tripping, as filtering capacitors can leak enough current to earth to trip RCDs, and with the number of drives in your machine, it could be leaking enough current to trip a typical 30mA RCD.

[jaypee89]

Do you have 3ph in your shop ?

Yes, testing with a 3 phase generator and have a digital phase convertor fitted for the permenant supply.

[jaypee89]

If things aren't earthed properly, then the various filtering capacitors in the drives/PSUs can cause floating voltages.

So I'd want to know why you have a "floating earth"?
All metal parts of the cabinet/machine should be earthed.
If they're not, then I'd be looking to see why they aren't.
It could be that somebody has disconnected them as a bodge to stop an RCD tripping, as filtering capacitors can leak enough current to earth to trip RCDs, and with the number of drives in your machine, it could be leaking enough current to trip a typical 30mA RCD.

The floating earth appears to be by design, All the standard expected earths are connected together on a terminal strip mounted inside the cabinet. The actual earth from the supply is connected to the neutral points on the system. It's a 3 phase no neutral system.
That's an interesting comment about the capacitors leaking to earth, something I can test further with

[m_c]

The floating earth appears to be by design, All the standard expected earths are connected together on a terminal strip mounted inside the cabinet. The actual earth from the supply is connected to the neutral points on the system. It's a 3 phase no neutral system.
That's an interesting comment about the capacitors leaking to earth, something I can test further with

That doesn't sound right.
The standard earths should be earthed, as that's safety critical.

I'm not sure why you'd earth the neutrals on a non-neutral system, or even why they'd have a neutral if it's a no-neutral machine.
Are there any transformers in the machine to isolate/step down voltage for anything?

[jaypee89]

Ye, took me a while to get my head around it, but it seems to be a legitimate thing. Welcome to google '3 phase no neutral floating earth system'. It's explained pretty well there.
My initial theory was, a line was drawing more current than the others, creating the imblanace, thus leading to the 70v on earth, but no luck chasing that, with the megger on 240v testing around for shorts to earth, found diddly'

There's no stand alone transformer as far as I know. All the motion and spindle controllers are directly from the 3ph 240

[m_c]

I should probably have used the correct term in my last post.
Any earth for protection purposes is what you'd technically call a Protective Earth (or PE for short). This is what the Earth is in your typical mains supply.
All the drives in your machine should have a PE, which is connected to Earth.

Floating neutral is a bit different. In the case of 3 phase, if you don't connect to a supply Neutral, the only way you'd have a floating neutral, is if you had something connected in Star (also referred to as Wye, but that's more a US convention).
Even on a machine that was fully isolated with/without a floating neutral, the structure would still be connected as a PE.

Now having realised exactly what drives you have, none of them are 3 phase, they all appear to be single phase 230VAC.
In the absence of any transformer, this would suggest that your machine should have a 3ph+Neutral supply (or possibly even just be single phase), and I'm also going to guess that none of your 3phase supplies have an RCD fitted, as the amount of current flowing through the earth is going to be well above RCD tripping current levels.

I'd suggest you trace the mains wiring to each drive, and figure out exactly how they're connected for power.