Mesa card grounding and shielded cables

I'm in the process of formally building my cabinet (rather than just the test setup) and decided to invest in some shielded cables for the internal wiring of the steppers, stepper encoders (closed loop) and connections from the Mesa to the stepper drivers.

Researching here on grounding the cable shielding raised another questions on grounding the Mesa card itself, so now I have two:

1. Should the Mesa card be grounded to the cabinet back plane (which is also earthed via the line in). I currently have the Mesa card screwed down (therefore grounded) through a 3D printed frame and it is currently working OK. (Partial build photo attached)

2. Can the cable shielding be grounded to the backplane (at one end only)?

Many thanks in advance.

Philip

Thank you Tommy

tommylight wrote:

fletch wrote:

1. Should the Mesa card be grounded to the cabinet back plane (which is also earthed via the line in). I currently have the Mesa card screwed down (therefore grounded) through a 3D printed frame and it is currently working OK. (Partial build photo attached)

I never do.
Although in some retrofit cases the whole machine is grounded and the 0 from power supply is also grounded, hence everything is grounded.

fletch wrote:

2. Can the cable shielding be grounded to the backplane (at one end only)?

Yes, if by backplane you mean the metal sheet attached by screws, and if that backplane is grounded properly at any of those screws.
Beware that paint will sometimes not allow good contact, so a bit of sand paper use is good.
 

Before I headed off to ebay to buy some nylon M3x15's I wondered why I'd taken the decision (when I first fitted it six months ago!) to ground it so checked the guide again - am I misunderstanding what 'frame ground' is? (top left of image).

 

The back plane on my cabinet is a separate galvanised panel but it is attached via copper coated bolts so will certainly be earthed/grounded - I kinda assumed (dangerous) this was the 'frame ground'. As far as I'm aware, the -ve of the 5v PSU is not attached to the ground, although the PSU itself is earthed.

Philip

Just checked and the -ve/GND is not connected to the screw holes, so will keep the stainless fixing screws.

I'm very impressed with the board (running with a Pi too) but given the cost of replacing it (UK :-/ ),  I'm slightly terrified of releasing the magic smoke! Would definitely recommend and use one again.

Thank you for your help - much appreciated.

My take is that the frame ground is attached to the enclosure frame which in turn is probably attached to the mains earth lead.
The Mesa cards are designed to be fully isolated so I think PCW prefers that the field power 0V shouldn't be attached to the frame.

As fas as the shielded cable, I would that the cables pass through cable grommets into the enclosure and attach the shield to frame ground at the drive end keeping the ground as short as possible. They say not to extend it. I then leave the shield unconnected at the stepper end.  If they are servos, then different rules apply and there was a good enlightening thread about that here a while ago. If you followed the instructions from Siemens, you'd need an  enclosure 6 foot high.
 

Thanks Rod - I believe my 0v is fully isolated on the Mesa board - there's no continuity between 0v and the fixing holes so hopefully OK.

All my shielded cables are inside the cabinet ie from the aviation connectors to the stepper driver & encoder (closed loop driver) and from the Mesa board to the stepper driver. I'm grounding them either next to the aviation sockets or next to the Mesa card as it's a shorter 'tail' - will upload a photo when I've done them.

Unfortunately the stepper cables that were supplied from StepperOnline are not shielded (the encoder ones are) but it seems to incredibly hard to source rubberised, flexible shielded cables, so I've stuck with the original cables outside the cabinet and the (stiff) Belden equivalent ones on the inside. The original cables weren't really long enough or I would have forgone the aviation connectors and gone straight to the driver via grommets.

Maybe my next project will have servos ($$$) but then I'd have to find room for a bigger cabinet

As do Treotham in Australia
treotham.com.au/

Look at the brands on offer and see if you can find them locally