Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 4 replies
  • Subscribers 32 subscribers
  • Views 858 views
  • Users 0 members are here
Options
You may also be interested in
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

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
    Pulses that are short compared to the time it takes for the signal to get along the wire are always a problem, and earthing in such a case is largely nugatory. And one way the common mode choke, (for that is the function of the  barrel of cable) works, is by allowing the signal so long to get used to being between the conductors of the cable, that it has forgotten which , if either side, was originally earthed, or off-earth  by the impulse voltage, when it set off.

    If it is any help we do not bother with curly pigtails to earth  racks in the HV facility here, but if they arrive with them on, we do not bother to take them out. It may very well be that the confusion is the result of a similar approach.

    Earthing for safety would normally be done via the mains leads, unless there are high leakage currents to consider, and then the mains lead develops an earthed screen , and maybe a side-along green and yellow. All of this is then choked to RF with ferrite beads -which are to all intents invisible at 50Hz, but as others have said, can make all the difference in the hundred nano-second domain.

    Apologies for the late response, I have been away from the internet, in any case others have it covered.
Reply
  • 0
    Pulses that are short compared to the time it takes for the signal to get along the wire are always a problem, and earthing in such a case is largely nugatory. And one way the common mode choke, (for that is the function of the  barrel of cable) works, is by allowing the signal so long to get used to being between the conductors of the cable, that it has forgotten which , if either side, was originally earthed, or off-earth  by the impulse voltage, when it set off.

    If it is any help we do not bother with curly pigtails to earth  racks in the HV facility here, but if they arrive with them on, we do not bother to take them out. It may very well be that the confusion is the result of a similar approach.

    Earthing for safety would normally be done via the mains leads, unless there are high leakage currents to consider, and then the mains lead develops an earthed screen , and maybe a side-along green and yellow. All of this is then choked to RF with ferrite beads -which are to all intents invisible at 50Hz, but as others have said, can make all the difference in the hundred nano-second domain.

    Apologies for the late response, I have been away from the internet, in any case others have it covered.
Children
No Data

Community Rules & Guidelines