Question about Earthing my data equipment

[sipxstream]

Hello folks,

Apologies in advanced if this is a daft question about earthing my data equipment in garage, but I'd rather be safe than sorry...

At the moment, we have a CU installed in the garage for lights and sockets, located at the front of the garage.

At the back of my garage we house IT data equipment within a data cabinet, including network switches, CCTV etc. Some of these network devices, including the cabinet itself, allow us to attach an earth cable to the housing of the metallic unit I guess as an additional safety measure. Can I run a 10mm earth cable from the CU to the data cabinet to provide an earth connection, or do I need to take it from the earth block within the meter cupboard outside?

Many thanks.

 

[poni]

yes, from the consumer unit should be fine,
but why do you want to do this? and why 10mm?
the unit has electrical equipment in the cabinet would have an earth connection in the mains plug if they needed one, a lot of stuff now is double insulated and does not need an earth,

 

[sipxstream]

Thanks for your input.

I just though it would provide increased protection, or at least reduced noise/interference? I only thought of doing this is because my old offices from where the equioment was removed from had an earth block attached next to the cabinet and had earth cables attached to the devices.

As to why 10mm, well it's because it's the only earth cable I have laying around.

 

[SPECIAL LOCATION]

Hello folks,

Apologies in advanced if this is a daft question about earthing my data equipment in garage, but I'd rather be safe than sorry...

At the moment, we have a CU installed in the garage for lights and sockets, located at the front of the garage.

At the back of my garage we house IT data equipment within a data cabinet, including network switches, CCTV etc. Some of these network devices, including the cabinet itself, allow us to attach an earth cable to the housing of the metallic unit I guess as an additional safety measure. Can I run a 10mm earth cable from the CU to the data cabinet to provide an earth connection, or do I need to take it from the earth block within the meter cupboard outside?

Many thanks.

Running a cable from these cabinets back to 'The CU' / 'meter cupboard Main Earth Terminal' would NOT be an earth cable! (A cable from the exposed metal work to the CU/MET would be a 'protective bonding conductor').

If these metal data cabinets are considered to be extraneous conductive parts,
i.e. liable to introduce an earth potential, (which personally I doubt?), then I could see a need for a protective bonding conductor. However the earthing arrangements for the electrical installation / garage installation, (TN -vs- TT), would need to be taken into account when assessing what size bonding conductor was needed. (10mm could be overkill, if it is needed at all?)

All adequate earthing should have been provided by the circuit protective conductor(s) of the sockets supplying any items of equipment mounted inside the cabinet. I would have thought all that would be needed is a short earth connection from the metal cabinet onto the CPC connections of the supply circuit.. (similar to an earth fly-lead from a socket back-box onto a double socket.)..

I can't see any need for the CSA to be greater than the CSA of the CPC of the supply circuit? If a fault occurred where the metal cabinet did become live, then the protective device(s) for the supply circuit should operate fast enough to remove any danger.

There are some situations where adding connections between metal parts can introduce greater hazards in the event of a fault..

Some things are hard to second guess over the internet.... It could be worth getting a qualified competent electrician round to check over exactly what your set-up is?

 

[Geoff1946]

With rack mounted equipment it is important to ensure that earthing is maintained between powered rack units and the cabinet independently of the rack mounting screws. This is because the mountings screws themselves do not usually guarantee a good connection, and also that individual rack units are likely to be removed live. That is probably what the earth studs you see are provided for.

 

[rjp44]

I can't see any electrical safety reason why you would want to run a separate CPC back to the MET and it may even introduce new dangers. Each device in the rack will have it's own adequate earth through the supply lead and, unless they are Class II, will each incidentally export that earth through the case to parts of the metal rack that they touch. This contact won't be reliable for each device, but it should reliably ensure that they can't export a dangerous voltage to the rack because of their internal earth arrangements.
The only thing that is a good idea is to connect the short earth jumpers which will have been supplied with the rack to any metal framed hinged doors on the rack itself. The pivot pins often run in plastic bushes so if a cable gets trapped in the door and damaged, it would theoretically be possible for the door frame to contact a live conductor and make the touchable part of the door live without an earth path to trip any protective device.

Most of the earthing stuff on 19" racks is for EMF protection of/from devices within them rather than electrical safety

 

[sipxstream]

I can't see any electrical safety reason why you would want to run a separate CPC back to the MET and it may even introduce new dangers. Each device in the rack will have it's own adequate earth through the supply lead and, unless they are Class II, will each incidentally export that earth through the case to parts of the metal rack that they touch. This contact won't be reliable for each device, but it should reliably ensure that they can't export a dangerous voltage to the rack because of their internal earth arrangements.
The only thing that is a good idea is to connect the short earth jumpers which will have been supplied with the rack to any metal framed hinged doors on the rack itself. The pivot pins often run in plastic bushes so if a cable gets trapped in the door and damaged, it would theoretically be possible for the door frame to contact a live conductor and make the touchable part of the door live without an earth path to trip any protective device.

Most of the earthing stuff on 19" racks is for EMF protection of/from devices within them rather than electrical safety

Thanks for the info. I believe you're correct, it's more for EMF protection rather than electrical safety, now that I think about it. In that case, perhaps it's not essential running a CPC back to the MET for this particular purpose.

However, the data cabinet might though...?

Would it be advisable to earth (or adding a protective bonding conductor) to the cabinet itself - and the removable side panels / door? I don't think I can rely on the powder coated surface to provide adequate protection as there are scratches all over, exposing bare steel.

You're the electrical experts though, and I obviously am not, so I'll follow your guidance; if you say it's not worth doing, then it's not worth doing

 

[Mike P]

If it needs earthing you will find specific lugs for that and the side panels will already have fly-leads in place.

 

[sipxstream]

It has specific lugs for the main body and fly-leads already connected to the side panels and door. I was just trying to find out if it's acceptable to run a 10mm earth from the cabinet straight into the consumer unit, which I think the answer to which is yes I can, but 10mm is overkill.

 

[binky]

It has specific lugs for the main body and fly-leads already connected to the side panels and door. I was just trying to find out if it's acceptable to run a 10mm earth from the cabinet straight into the consumer unit, which I think the answer to which is yes I can, but 10mm is overkill.

Can't see anything wrong with that if that's what you want to do.

 

[apprentice87]

If you DO run an earth cable, it must connect to the same earthing point where the supply that feeds the cabinet is taken from. You cannot "mix and match" earthing.

Secondly, why is the cabinet not already simply connected to the CPC of whatever cable feeds it??

Thirdly, it, [as you describe it [and has been pointed out] is more of a bonding cable than an earth, so things are not so simple.. TNCS anyone??

To be honest, i think you are liable to create what could be severe danger, rather than improve things...

I would just leave things alone

john..

 

[sipxstream]

Thanks, John.

Apologies if I've misunderstood you, but there isn't any kind of electrical feed going directly to the cabinet; all it is is a metal box that houses rack servers and switches. Each of the servers/switches have their own CPCs. However, some of these servers/switches have a screw terminal on the metal case, which I believe are more for noise reduction rather than for electrical protection.

There is also a lug on the main cabinet for an earth/bonding cable, and then fly-leads that go to the removable side panels and the door of the cabinet.

I just thought it was a case of simply running a cable from the CU to the cabinet, and wasn't really aware of any potential danger.

If the general consensus is that it won't provide any significant advantages, but an increase in danger, then I'll take your advice and will leave things alone.

Thank you to you all for educating me.

 

[Mike P]

The mobile racks we used in broadcast TV had 10mm earth cable connected it was a multi strand (very fine) not like the solid 7/9 core in general earthing but if it’s a fixed rack that’s not an issue.

 

[sipxstream]

Thanks Mike.

Was the earth connected to the mobile racks in order to reduce interference with the broadcast equipment?

 

[apprentice87]

Thanks, John.

Apologies if I've misunderstood you, but there isn't any kind of electrical feed going directly to the cabinet; all it is is a metal box that houses rack servers and switches. Each of the servers/switches have their own CPCs. However, some of these servers/switches have a screw terminal on the metal case, which I believe are more for noise reduction rather than for electrical protection.

There is also a lug on the main cabinet for an earth/bonding cable, and then fly-leads that go to the removable side panels and the door of the cabinet.

I just thought it was a case of simply running a cable from the CU to the cabinet, and wasn't really aware of any potential danger.

If the general consensus is that it won't provide any significant advantages, but an increase in danger, then I'll take your advice and will leave things alone.

Thank you to you all for educating me.

I am a dummie where computers are concerned.. I do not know what you mean when you say; "but there isn't any kind of electrical feed going directly to the cabinet; all it is is a metal box that houses rack servers and switches. Each of the servers/switches have their own CPCs"

Whatever these contrivances are, they are powered up from somewhere??

What you must do, is to make sure that you get the earth from the same circuit that powers up this stuff in the box.

It is hard to explain, but a circuit comprises the "live" the neutral, the earth, and devices [breakers, fuses and/or RCCBS] that act together to provide ADS, that is automatic disconnection of supply in the case of an earth fault, this being a fault between a live conductor and earth.

The power has to be shut off a bit sharpish, as all metal parts will be above earth potential for the duration of the fault. This is why you have bonding, so that if your metal fridge has a fault, and the casing rises above earth potential, so does your metal sink, in unison.

This means that if you are touching both at the same time, no current flows through you, as no potential difference between fridge and sink to drive it..

I cannot remember the technical wording, [it is 4am as i write this] but in the same way as you would not take a "live" from one circuit, a neutral from another, you cannot take earths and mix and match them..

Another problem you could have, is it is swings and roundabouts.. Yes, it sounds a great idea to bond the box, but remember this, there is a downside too..

IF you have a fault in the supply to the box, then the ADS should cut the power off very quickly.. The exact time depends on the arrangements for ADS, but it will be a fraction of a second.

However, it is PERFECTLY possible, that due to a fault "out in the street" that your metal box in the garden, could be SERIOUSLY live for days and weeks if bonded to earth from the house..

if it were me, i would be making sure that whatever power went into the box, went through an RCD, absolutely definitely..

I cannot say much more than this, because i do not understand what it is you have in there..

john..

 

[Mike P]

Thanks Mike.

Was the earth connected to the mobile racks in order to reduce interference with the broadcast equipment?

No, I think it was more of a safety thing, extraneous metal, and all that