Within the comms room it will be possible and is sensible to bond everything together to a common earth - if you had a large hall of kit a mesh might be better, but  a few racks is scarcely that.

Another rack 240m away is essentially out of the EMC zone , and you should assume that the earth voltages could be quite different on a microsecond scale - is it connected by fibre or by twisted pairs to the comms room? (In many ways if you can justify the outlay then fibre makes things much easier. ) Also relevant are the external signals coming in - yo uhave to imagine that they might be at different voltages ,and you do not want anything delicate to end up 'doing the splits' with one interface connected to something at a completely different voltage, The trick then is to marshall the in coming lines such that services are interconnected and therefore not able to be too far apart voltage-wise before they hit the expensive equipment.

If you ever end up designing a nuclear bunker that means all in bound cables for antennas, network cables, power  and so forth have shielding armour that terminates on a common of access panel. For commercial situations the stresses are not so extreme, but the principles are very much the same - you are only trying to prevent overstress of the electronics, and more or less normal ADS.

Thank you very much for your response.


Apologies for late reply, been out all day in meetings.


All backbones are fibre, copper incomer is only for lift and alarm lines and goes to the main data cab.


I have done a shoddy little sketch to illustrate my thinking.



 


 

Given what you are trying to accomplish that looks like a sensible basis. Now what plugs into the racks, and where does it get its power? The potential for earth loops in that direction  also need to be considered.

HI me1899 you said, "Am I right in thinking that each satellite cab is to have a 4mm g/y to a brass earth block adjacent (secondary bonding busbar) and then connection onto a 16mm conductor back to a primary bonding busbar which in turn connects to the MET? Am finding the standard a little confusing. 42U to have a 16mm connection?"


Please consider I'm no expert on earthing and bonding - but I'd suspect that if your warehouse is made of a metal framework structure, and  bonding needs to run back to the MET somehow, you could consider using this metal framework - so no need for giant scissor lifts and running hundreds of meters of earth all over the warehouse (huge additional cost) to get back to the MET, just connect any underfloor rack bonding if required to the metal frame of the building. This in turn is connected to the MET. 


Kind Regards


Tatty

Thank you both very much for your replies, much appreciated.


Sorry again for late response, but I tend to flit about here and there.


Mapj1 - in answer to your question just standard and PoE switches and small rack mount UPS units (3kVA in the main rack, 1.5 in others), and that is it. Each cab location has a local DB next door - not dedicated to the cabs (other than main one), but just convenient to locate there.


Tattyinengland - good point, it is also mentioned in the BSEN 50310 so can go that route.