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andy586
02-07-2014, 05:26 PM
I understand from reading about noise issues that you earth a shield at one end only to avoid ground loops.Do you need to worry about ground loops created when earthing themachine for safety purposes? For example, if I earth the machine frame and I earth the spindle body, does this create a ground loop (because the two are connected) and is this an issue? Would I be better off with one earth and then ensuring conductivity between all parts of machine?

Also, should a BOB be earthed (currently powered by an old phone charger with only two wires)? And should my PC earth be connected to the main earth point for everything else?

Many thanks for any replies as always.

Clive S
02-07-2014, 06:05 PM
I would connect the machine frame to your star point, don't worry about the pc because it will be opto isolated the spindle will be earthed back to the vfd ..Clive

JAZZCNC
03-07-2014, 02:09 AM
Also, should a BOB be earthed (currently powered by an old phone charger with only two wires)? And should my PC earth be connected to the main earth point for everything else?

Ok common misunderstanding Here.? Your mixing up AC Earth and DC negative. They are very differant and should not be mixed up.
Your BOB will be DC and the Charger is converting AC to DC so your Phone charger is the only thing that should be connecting to EARTH not the BOB.(If charger as Earth often Don't)

Same goes with Other DC powered components IE: Drives etc. Only the Earth of the supplying Transformer should go to the Star EARTH point. Any DC Negatives should go to the (-) of the DC side of the supply.

One end of shields for things like Steppers, Limits, Homes etc go to the Star EARTH point. The spindle cable from VFD to spindle is the Only exception and can be connected at both ends and then it's best to run it back to Earth point on VFD. If the VFD is then powered from same AC supply in control box then run it's earth to the Star EARTH point.

Run Machine frame Earth back to Star EARTH point. Don't Earth the PC case and best to run it from separate supply to Control box.

EddyCurrent
03-07-2014, 10:21 AM
What happens then if using a zero touch plate for Z ?

JAZZCNC
03-07-2014, 01:12 PM
What happens then if using a zero touch plate for Z ?

You being a smart arse Eddy current or you seriously asking because you don't know.? Because I'm pretty sure you DO.!!

EddyCurrent
03-07-2014, 01:15 PM
Just asking on behalf of andy586 as he may come across this requirement later and I didn't want to steal your thunder by replying myself.

JAZZCNC
03-07-2014, 01:44 PM
Just asking on behalf of andy586 as he may come across this requirement later and I didn't want to steal your thunder by replying myself.

No your being a smart Arse Eddy but just for the sake of others and Andy586 I'll answer it.

To be 100% sure touch probe will work then you should use Input (+) & (-) terminals with Clip to spindle and Plate for touch off. Yes Spindle may be connected to Earth thru the BOB but you don't know that for sure and actually better quality BOB's or Motion control cards with direct I/O (Like CSLAB's products) don't actually allow this to protect there inputs and protect against Noise etc so force you to use dedicated Negative so they know every thing is at the same potential.

Just because it works doesn't mean it's correct way or actually safe for the BOB.!

EddyCurrent
03-07-2014, 02:05 PM
No your being a smart Arse Eddy . . .

That's fine, see Ya !

JAZZCNC
03-07-2014, 03:34 PM
That's fine, see Ya !

Well why ask a question you know the answer too that Even the OP didn't ask.? . . . . That's just trying to be a smart arse IMO. Now I'm actually using Mrs Brown's "Elctrocution Lessons" these days so I'll just say . . . 'That's Nice'.!

andy586
11-08-2014, 05:28 PM
Many thanks for the replies. Got it all sorted now. Much appreciated!