[Cware]

I've bought a cnc machine recently which I'm modifying.

It runs on 220V mains.
The drivers(slo syn2000) for the steppers take 110V AC

So there is a transformer between them which converts 220V to 110V.
I've checked and there is no electrical connection between primary 0 and secondary 0 so I figure it's an insulating transformer.

The thing is whoever did the wiring was really sloppy, in the drivers only L1 and N are connected and PE isn't.
Now PE is connected to the case of the driver which is bolted to my Case so there is an earth connection to the primary side present.

Been reading up on this a lot in the past few hours and I concluded that from a safety point of view; I can connect the PE to the Primary PE (case)
and that I shouldn't connect the secondary 0 to PE
I'm however concerned that the PE isn't protecting anything anymore since the insulating transformer is galvanic insulated.

1)What would happen in case of a short circuit between secondary and case?
From what I've read that would be safe to touch the case but the circuit breaker wouldn't trip.

2)What would happen in case the secondary shorted out?
Again from what I've read the transformer windings would melt before the circuit breaker trips.

3)Would the drivers be safe as connected to primary PE?
I guess not?




Btw I'm about to tie all DC Negatives from the 24V,5V and 12V PSU's to the case as well.



Could anyone clarify this?

[Al_The_Man]

What you are concerned about is now that you have galvanic isolation between pri and sec you have no earth protection?
If the resultant DC supply from the secondary is referenced to earth ground, then if you connected the sec. (AC) winding to earth you would blow the DC power supply.
So, in most cases, either the AC sec. OR the DC supply common from that sec. can be earth grounded, (not both), if anything, it is usually the DC common that is grounded.
All earth grounds will preferably go back to a star point ground connection together with the service ground.
BTW, if using a P.C. the P.S. common is usually connected to earth GND in the P.C.
Al.

[Cware]

Thanks al
The drivers take AC ,it's not rectified to DC.
I have separate supplies attaching directly to 220V for the dc voltages.


Attachment 251194


Pic is my setup

My concern is that the driver isn't properly grounded since the secondary is insulated and wouldn't trip the circuit breaker in case one of the motor cables shorted out.
Not sure what would happen would the transformer windings melt?
Does the overcurrent protection even kick in like this, read somewhere it may not .

I don't want to risk damage to the driver due to unproper grounding.

Is it safe to run a setup like that.

[Al_The_Man]

Grounding isn't going to save a motor cable shorting, that should be taken care of in the drive.
in the SloSyn drive there is a DC power supply, this is then converted to some form of variable voltage, probably PWM to control the motor current.
It is best to earth ground the motor frames to prevent spurious noise in the low voltage control electronics.
http://www.automation.siemens.com/do.../emv_r.pdf?p=1
Al.