Stepper wiring RE shield/ground/connector

[TravisR100]

I have steppers that are being driven with a Xylotex board. It supplies a max of 2.5A per motor. They are 4 wire steppers. From what I've researched it seems that 20AWG wire will suffice. I've also read that I need to use shielded cable for the steppers. My question is what to do with the shield. Does the wire itself simply need to be shielded or should the shield actually be connected in the cabinet, at the motor, or both? If it needs to be connected at either end then I assume I'll need a 5 pin CPC connector instead of 4 so that I can carry the shield through and connect it to a ground somewhere. Any advice?

I'm looking at this cable. Good choice?
http://www.lappusa.com/Spec_Template.asp?nGroupID=10114

[Al_The_Man]

To ground the shield you either need to bare a section of the shield and clamp it to a earth ground clamp, or if it has a separate bare drain wire, this can be used to connect it to a star point earth ground terminals or ground plate.
All the supply grounds, shields and service ground should be connected here.
See section V11 http://www.ese.upenn.edu/rca/instrum...round/grd.html
BTW, the cable is fairly high quality industrial type.
Al.

[TravisR100]

Ok, so I'd actually need a 5 pin CPC connector to carry the shield through to the inside of the electrical cabinet where I would then tie it to earth ground. But what about the motor end? Do I tie the shield to anything on that end?

[TravisR100]

And wow, thanks for the link. That's great information!

[Al_The_Man]

I forget to mention, only one end of shielding is connected to Earth Ground. If this is done in the cabinet, it can tie directly to the ground terminal/plate set-up.
Al.

[Crevice Reamer]

Unless you are running more than 5A, #22 wire is perfectly adequate. Shielded Twisted Pair is the prefered wire type.

You can use THIS wire for motor cables and home/limit switches. Ground the drain wire ONLY at the driver end.

http://cgi.ebay.com/ws/eBayISAPI.dll...2BSI%26otn%3D4

CR.

ETA: Looks like Hubbard is OUT of stock on that wire. Sorry!

[Al_The_Man]

Originally Posted by TravisR100 And wow, thanks for the link. That's great information!

I agree with most there except the very last item.

"d. Analog/Digital Grounds
In general, analog and digital grounds should be kept separated and connected together only at one single point."

In fact virtually every non-laptop PC has the mother board connected at ground potential through the mounting screws.
So I prefer to bond (ground) the PC supply common direct to the ground bus. without relying on it wending its way through the mother board. This eliminates or reduces all the spurious noise entering the parallel port route.
With motor conductors, you want to keep the radiated energy in, twisted conductors and OA shield should suffice, for encoders or inputs, you want to keep radiated energy out, therefore twisted shielded pairs is a good option.
Al.

[TravisR100]

I've been doing some more reading and searching. I have to admit I'm still a bit confused. If I get a 5 conductor cable with shield where one of the conductors is not a "bare drain wire" but an insulated green/yellow ground (this is for the 4 wire steppers) does it matter if I choose to ground the green/yellow ground wire or the shield at the cabinet? I suppose as long as one of them is grounded that's OK? And it should only be grounded at the cabinet end? Not the motor end?

Also, Al, you talk about a grounding plate or grounding bus in the cabinet. Can I not simply use the metal backplate that the electronics are mouted on as the grounding plate?

BTW, I don't know if anyone's posted a link to this site before but it's a great starter for anyone who's not up on electricity. http://www.allaboutcircuits.com.

[Crevice Reamer]

The bare drain wire is CONNECTED to the shield. Only by grounding the shield do you get any benefit.

Shielded wire for motor cables is OPTIONAL. Motors can work with or without shielded cables.

Shielded wire for Home/Limit switch wiring is MANDATORY. Without shielding, stray currents can cause all sorts of problems for you.

CR.

[TravisR100]

I was looking at cable that had an insulated ground wire as well as shield, not a bare drain wire. But your explanation certainly answers my question about the wires. Thank you.

[Crevice Reamer]

What you want to find is shielded stranded double twisted pair 22 AWG wire. It looks like this, only 2 pairs instead of 4. If you are only using it for Home/limit switches, it could be smaller--24 AWG.

CR.

[TravisR100]

Know where I can get that with 2 pairs in an oil resistant cable?