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Connection to earth of computer rack drawers

Zs
Hello friends, greetings from the desk where I find myself a bit stuck on something.


I wonder if you could guide me to something definitive on the subject of the earthing requirements for the moveable parts of computer racks please


I'm referring to the ones with slide-out drawers/ trays onto which a device is mounted, such as a UPS or an oscilloscope.


My canters through first the regs and then the web don't find what I was expecting. The web leads me to differing advice - from curly tails (which I thought were frowned upon) to  welding the trays in place.  


The rack in discussion is carefully bonded at the base, covering all metalwork and providing a reading even from each movable tray (when in place) of <0.05 ohm. Each scope of course has it's cpc but only half of them have a curly tail connecting them to the metal work.   I therefore reckon that half are compliant and half not.


Any advice?

Thank you...


Zs












Parents
  • 0
    Well,  thank you both for the replies.  In our case, we are first institutionally so risk-averse that you have to wonder how anything ever gets done , so the safety aspect is at the heart of the enquiry.  Nobody wants to be found omitting anything.  But then, on a much more interesting level;   Graham's reason 'for' applies - the rack contains measurement instruments sensitive to high frequencies and radiated / conducted emissions.  Because we are a pulsed power operation, you can imagine what happens for that critical nano second (or micro second for the slow stuff) and it is happening to our measurement devices just at the point when we need the information. There is a noise issue.


    I have a confession to make - this is on a par with the day Zs admitted that she liked a range of LED lights and Andy J posted 'who are you and what have you done with Zs?' ...

    I obtained a copy of BSIEC 61000-5-2 following your post Graham and have spent quite a bit of time reading it.  What an excellent standard it is.  Clearly written by a knowledgeable enthusiast and such an education.  It's like reading a tutorial not a dictatorial. Thank you for that.  I reckon I should read it in secret and just pretend I knew all that ;).   Complete with pictures of the effect of curly tails and I'd never before have given a thought to the use of round or flat braids - and so on.


    Our signals largely get back to the scopes via fibre optics by the way.


    Andy, you are right about the ball bearings and you may well be right about not dealing with the EMC.  There are already various layouts of ferrite rings around the place and even a huge plastic barrel, wrapped with about 100m of flex for insertion into the circuits by way of mitigation.  That last one might seem a bit Heath Robinson but it works, after a fashion.


    Thank you, I now have to make a decision on what they should do with the racks and offer it forward.  


    Zs

     
Reply
  • 0
    Well,  thank you both for the replies.  In our case, we are first institutionally so risk-averse that you have to wonder how anything ever gets done , so the safety aspect is at the heart of the enquiry.  Nobody wants to be found omitting anything.  But then, on a much more interesting level;   Graham's reason 'for' applies - the rack contains measurement instruments sensitive to high frequencies and radiated / conducted emissions.  Because we are a pulsed power operation, you can imagine what happens for that critical nano second (or micro second for the slow stuff) and it is happening to our measurement devices just at the point when we need the information. There is a noise issue.


    I have a confession to make - this is on a par with the day Zs admitted that she liked a range of LED lights and Andy J posted 'who are you and what have you done with Zs?' ...

    I obtained a copy of BSIEC 61000-5-2 following your post Graham and have spent quite a bit of time reading it.  What an excellent standard it is.  Clearly written by a knowledgeable enthusiast and such an education.  It's like reading a tutorial not a dictatorial. Thank you for that.  I reckon I should read it in secret and just pretend I knew all that ;).   Complete with pictures of the effect of curly tails and I'd never before have given a thought to the use of round or flat braids - and so on.


    Our signals largely get back to the scopes via fibre optics by the way.


    Andy, you are right about the ball bearings and you may well be right about not dealing with the EMC.  There are already various layouts of ferrite rings around the place and even a huge plastic barrel, wrapped with about 100m of flex for insertion into the circuits by way of mitigation.  That last one might seem a bit Heath Robinson but it works, after a fashion.


    Thank you, I now have to make a decision on what they should do with the racks and offer it forward.  


    Zs

     
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