Control Cabinet EMI RFI Glands and Clips

[Project_Hopeless]

I'm not sure if this is the best sub-forum for this question, but here it is.

I have a hobby build with stepper motors and limit switches. All the control components are in a metal enclosure. I'm looking for a low cost effective solution to ground all the shielded cables entering my control cabinet. I've looked at the grounding bar style clips but those still require a ground bar and a grommet or plastic gland entering the cabinet. I could go with an EMI gland, simpler but at first glance more $$.

What cost effective solution have you used or recommend? Where have you sourced the materials?

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[wizard]

It really depends upon the cable and how it is being used. For example some of the servo drives, even some stepper drives, provide for a clamping area to terminate the cable right at the drive. In some cases people will do the same to the panel. So the answer sometimes is to resist skinning the cable to ground the shield at box entry. Instead the shield is grounded as close to the drive as possible.

As you have noted some requirements mean grounding the shield close to the entry point possibly on a grounding bar. I suppose the local jurisdiction has a big say in how this is done. Personally I’d rather see as little damage done to the cable as possible which would mean grounding at the drive. In an ideal world the cable runs from stepper / servo to the drive, unbroken and free of splices. The only negative with respect to bus bar grounding is that the ground straps tend to crush the cables which I don’t like. My dad his toon is that a sure way to cable failure is to pinch it or kink it, that is to concentrate stress someplace in the cable.

[mactec54]

I'm not sure if this is the best sub-forum for this question, but here it is.

I have a hobby build with stepper motors and limit switches. All the control components are in a metal enclosure. I'm looking for a low cost effective solution to ground all the shielded cables entering my control cabinet. I've looked at the grounding bar style clips but those still require a ground bar and a grommet or plastic gland entering the cabinet. I could go with an EMI gland, simpler but at first glance more $$.

What cost effective solution have you used or recommend? Where have you sourced the materials?

Your metal cabinet will be Grounded so just inside the cabinet you can Ground the Shield if you can't find any cheap Glands for Shield Grounding, I will be making them soon as I found the same problem in finding them at a reasonable price, Just make sure your Cabinet has a Star Point Grounding Post, also where ever you do your Shield Grounding remove any paint

Here are some ideas for you

[joeavaerage]

Hi,
whether you ground the shield as it enters the cabinet or at the drive depends on the nature of the EMI/RFI you are trying
to avoid.

If you are concerned about EMI OUTSIDE the cabinet then earthing at the cabinet entry is desirable. The cabinet, presumably steel,
is an ideal low impedance earth. If you have ten cables all entering and earthed the impedance between cable entries is lowest if a conducting
'earth plane' is used which is a very fair description of the exterior of a steel cabinet.

If however you are concerned with EMI WITHIN the cabinet or 'crosstalk' between circuits then earthing at the cable termination is desirable.
The drawback of that approach is that each of the cable termination earths should be taken to a single star point. Thus there is a wire between
the cable shield located at the drive and the star point, maybe several inches or even feet depending on the size of the cabinet and the placement
of the drives relative to the star point. A single wire has an impedance at EMI/RFI frequencies and this impedance counts directly AGAINST the shielding
effort.

Mactec's solution of earthing at the cabinet entry is very simple and elegant. It would be my preferred approach UNLESS there is 'crosstalk' within the cabinet.

Craig

[Project_Hopeless]

Your metal cabinet will be Grounded so just inside the cabinet you can Ground the Shield if you can't find any cheap Glands for Shield Grounding, I will be making them soon as I found the same problem in finding them at a reasonable price, Just make sure your Cabinet has a Star Point Grounding Post, also where ever you do your Shield Grounding remove any paint

Here are some ideas for you

Those isotek clamps looked like a perfect solution but the price for a simple stamped and bent metal strip surprised me. any recommendations on a inexpensive source?

[mactec54]

Those isotek clamps looked like a perfect solution but the price for a simple stamped and bent metal strip surprised me. any recommendations on a inexpensive source?

You may find some clips that will work at a Hardware store, it's finding one that is the right size for your cable size is usually the problem, with some copper strip you can make your own just form it around a steel rod like below not that hard to make, yes the Icotek are the best but can get expensive

The smallest I have found was 8mm to 10mm look up Terry clips you may get lucky and find something that will suit your cable size