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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












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  • 0
    +1 for avoiding curly pig-tails. If you did need something then a flat braid is usually a better choice.


    That said I'm not convinced of the need for anything. If it's for shock protection (because someone thinks the shelf could be an exposed-conductive-part if a flex gets trapped in the sliding mechanism somewhere) then there are probably better solutions - e.g. cable management arms that concertina down when the shelf is pushed home) to stop flexes getting trapped in the first place.


    If it's for EMI I doubt the curly tails will have much effect - there will almost certainly already be good contact between the shelf and the main body of the rack - those slide rails are usually full of steel ball bearings and so have multiple points of contact despite any grease etc. Besides the earthed outer shell of the rack provides the main 'Faraday cage' all the shelf could do at best would be to reduce the interference between one item of equipment and the item below it- and if they were that sensitive (or noisy) I've expect them to have their own earthed enclosures anyway.


      - Andy.
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  • 0
    +1 for avoiding curly pig-tails. If you did need something then a flat braid is usually a better choice.


    That said I'm not convinced of the need for anything. If it's for shock protection (because someone thinks the shelf could be an exposed-conductive-part if a flex gets trapped in the sliding mechanism somewhere) then there are probably better solutions - e.g. cable management arms that concertina down when the shelf is pushed home) to stop flexes getting trapped in the first place.


    If it's for EMI I doubt the curly tails will have much effect - there will almost certainly already be good contact between the shelf and the main body of the rack - those slide rails are usually full of steel ball bearings and so have multiple points of contact despite any grease etc. Besides the earthed outer shell of the rack provides the main 'Faraday cage' all the shelf could do at best would be to reduce the interference between one item of equipment and the item below it- and if they were that sensitive (or noisy) I've expect them to have their own earthed enclosures anyway.


      - Andy.
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