Rubbish Grounding Post

[StrataNet]

Hi guys,

We've got a WS-12-250-DC that I needed to ground. I ran a new 16mm2 cable from my Earth bus (I probably could use 10mm2 but I like to go a bit thicker just to be sure) and up to where the switch was. Then I noticed that the grounding post on it is very small! Anyway, I unscrewed the tiny little screw and fit it to the lug on my cable. As I was gently screwing it in, the whole grounding post sheered off - it was very flimsy and turned out it was only attached to the metal case. I assumed that it would have a proper post which internally attached directly to the PCB.
For now I'm going to attach it to one of the rack screw holes (it's mounted upside-down to a peice of wood) for the interim but it would be good in the next revision of this switch (and probably other models too) to have a decent solid grounding post with a wing nut or similar. Switch grounding is very important and to have the post sheer off with very little torque is a shame. Photos below:





Thanks,
Richard.

[sirhc]

I am sorry your grounding lug came lose, I am sure a small percentage could fail due to improper installation at the fabricator but we pre-install the ground screw with a torque screw gun so it usually will expose any PEM nut not installed properly.

The most common reason I have seen the PEM nuts spin out is from cross threading the screw then when you try to force it in or force it out if the cross thread is seized.

I forget how many ft pounds they are rated for but it is a decent amount.

The chassis is made of conductive zinc coated metal and the chassis is connected to the ESD RJ45 jacks via the zinc stand off posts next to the RJ45 stacks. The PEM nuts are installed prior to powder coating so they have a good conductive connection as you can see in your picture where the powder coating is missing where the PEM nut came out.

[StrataNet]

Hi @sirhc, thanks for your quick reply.

It may have been a defective unit as I had barely touched it when it came loose - I hadn't gotten to putting any decent torque onto it when it sheered off. Looking at it visually it does look like a fairly weak attachment though, I'd be interested to hear if anyone else has come across the same problem.

However it is a bit small for those of us who want to put any decent sized cable onto it; a larger post would be preferable. In my opinion each device should be grounded with at least 10mm2 copper.

[sirhc]

12 AWG with a through hole crimp end is sufficient grounding wire but if you wanted over kill you could use 10 AWG with a through hole crimp.

In my opinion anything heavier would be WAY over kill considering the (12) ESD drain wires would not have the capacity of 12AWG.

[StrataNet]

Hmm interesting thought, but we usually use Ubiquiti Carrier cable at our high sites which has the shield too which adds to the ground. I see what you're saying though and the antennas that can be grounded are grounded which certainly helps (can't say much for NanoBeams and Rocket M5's though).

If I get time when I'm in the area tomorrow I'll head to site and reassess.

[sirhc]

Yea, I hope you run dedicated ground wires to all antenna and mounts.

Also the intended grounding wire path should be shorted than the Ethernet run.

Here are 2 great posts on grounding.
viewtopic.php?f=30&t=188
viewtopic.php?f=30&t=1429

[sirhc]

Something in the line of this is what we had in mind for that lug.

ground1.jpg (39.98 KiB) Viewed 4109 times

[StrataNet]

Yeah I've read both of those grounding posts already - they've been very helpful, thanks! And cool, I'll make sure I get some smaller wire next time.

Cheers.