Earthed Switch Cabinets

[Dos_Box]

Does anyone here in CLEO land have any wall mounted cabs that are not earthed? It was mentioned at a meeting the other day and I'm just curious to see if people have any ideas.

[ChrisH]

This was mentioned last year as well. Ours is not earthed and when I mentioned it to a visiting engineer he didnt know what I was on about . Edited September 19, 2008 by ChrisH

[Hightower]

Oops, didn't realise it was regional - I voted no. Sorry

[ChrisH]

Oops, didn't realise it was regional - I voted no. Sorry

 

I removed your vote.

[Hightower]

Cheers

[Paul_L]

lots of my primary schools still have not had them earthed, which I guess will effect the install of the new CLEO network edge devices, yes?

 

Paul

[plexer]

Why does a cab need to be earthed?

 

Ben

[Geoff]

Because if the equipment in it has an earth leakage this is discharged into the case. In some cases this will lead to the cabinet casing becoming live. Electrocution does not make for a happy network engineer.

[ChrisH]

We have a lot of radio stuff on our roofs although its being phased out. They are probably bothered about lightning etc. I think somebody got a shock from some dodgey electrics as well.

[Geoff]

You should have a lightning conductor on your building(s) to protect against lighting strikes. Earthing your cabinets makes your networking equipment more vulnerable to lightning, as the route to ground has less resistance.

[jmcdermott]

i am confused.

 

If all PC cases are earthed via the psu, and the rack mount cases are connected to the comms cab via metal brackets and screws, then surly all comms cabs are earthed.

[Geoff]

I'm not sure about your building, but round here ours are made out of concrete and brick. They tend to be great insulators.

[torledo]

i am confused.

 

If all PC cases are earthed via the psu, and the rack mount cases are connected to the comms cab via metal brackets and screws, then surly all comms cabs are earthed.

 

It's a strange one isn't it.....best practice says that all racks and all equipment within racks should be connected to a telecoms ground busbar (TGB), this busbar would then connect to a common bonding network (CBN), which would then connect to the entrance facilitiy grounding busbar....think of the TGB as a connection point in a server room to where the 6 AWG earth cables from switch chassis and racks connect to....

 

in our building the earth for our water pipes, ceiling gred, ventilation system all terminate at the entrance facility ground (this is also sometimes referred to as a main grounding busbar)

 

ofcourse all power distribution boards have their own earth, but a telecoms earth is supplimentary bonding....technically it's not good enough to rely on the earth to the equipments power supply and it's not sufficient to have an earth wire connecting the door of the cab to the chassis (if your going to earth a cab it has to actually go to earth) - for safety reasons and for ESD safety....all racks and equipment within racks should be connected to a common ground to maintain equipotential. The common ground would then terminate at the entrance facility ensuring a proper earth.

 

The real question is how many schools have a telecommunications grounding network ? Not how many have got a earth wire connected to their wall mounted cabs

 

We don't have a telecoms ground network, i'm tempted to implement a TGB for our racks and then connect that to the nearest celing grid/ventilation system ground point (it's a short cut)....although i'm told this isn't best practice. Things like wire baskets and the interconnections between ladder racks also need to be bonded....again not many people realise it let alone do it.

 

Best to bond all racks, individually bond equipment that ships with ground lugs i.e some switches, and bond wire baskets to ground. Panduit sell the kit to do it, but connecting an earth wire to a rack without it actually going back to the entrance facility is totally pointless. And no the earth of items of kit and pdu's going back to a power panel is irrelevant. Telecoms bonding is supplemental.

 

I'm no expert but i've done a lot of reading and it's THE most misunderstood aspect of data center design....i'm glad this thread sprang up because the topic is so overlooked.

[jmcdermott]

OK time to start digging and putting them rods in place!

[plexer]

I wondered why the 2600-48 we just bought had a little earth wire in with them.

 

Ben

[torledo]

wonder those that do have 'earthed' cabs....how are they earthed ?

 

I don't mean merely the short length of earth cable, but whether they've actually got a telecoms ground bar, or something that can perform the role of a telecoms ground bar and common bonding network i.e overhead wire baskets running back to the entrance facility....or as i suspect, nobody has a clue....they see a little green and yellow wire connected to their wall cabs and assume they are 'earthed' without having a proper grounding and bonding facilitiy and without having earth potential readings taken between cabinets ?

[timzim]

I'm not sure about your building, but round here ours are made out of concrete and brick. They tend to be great insulators.

 

Sorry Geoff, they're not necessarily good insulators. Brick, especially new brick, can be slightly radioactive and therefore actually attracts lightning - radioactivity ionises the air as it's emitted, making nice little pathways for electrical currents to travel along. Concrete, if it contains rocks such as granite, may well be radioactive too. On the bright side however concrete structures tend to be big steel cages clad in concrete, and the steel goes deep into the ground. If you can remember your GCSE Physics (what?when?) there's no charge on the inside of a hollow conductor (e.g. a big metal cage) so any lightning which strikes your building won't actually enter the building but will pass, via the building, straight to earth.

 

The only way lightning will damage your equipment is if some electrical switchgear nearby gets hit and you get a big surge through the supply, but then you should have a UPS in the way to protect against mains surges. If you do get struck by lightning falling concrete might be your biggest problem if your buildings are as rubbish as ours.

[john]

Don't know about my current place but didn't have any in my last place that were earth bonded, and we were quite hot on electrical safety and that stuff. I'd guess that no is probably the answer but I may be wrong so please don't shoot me if I am as I haven't checked them, but it just doesn't seem common.

[Geoff]

The only way lightning will damage your equipment is if some electrical switchgear nearby gets hit and you get a big surge through the supply

 

Some of us have wifi deployed with external outdoor antennas. If one gets hit. It's a great way to fry your data network. I seem to recall there have been a couple of threads where this has happened to people.

[SYNACK]

Some of us have wifi deployed with external outdoor antennas. If one gets hit. It's a great way to fry your data network. I seem to recall there have been a couple of threads where this has happened to people.

 

You really want lightning suppressors like these if you have external antennas, they are not full proof but they do provide lots more protection than nothing at all. Best bit is they are stupidly cheap in comparison to the damage that they can prevent.