Cable in trunking in Computer suite

[carlday]

HI

In a IT suite at a local school we have dado tunking with Cat5 and power in it. The sockets are wired on 20amp radials 3 or 4 sockets on each trip. They are wired in 2.5mm Low smoke single. We have had some sockets moved and they have been wired from the first socket on the radial (Low smoke connecting this socket to distrbution board) in 2.5mm T&E with a 4mm bond cable between earth terminals on the new sockets.Am I right in thinking this wrong and should have been done in low smoke cable or is it going to be ok.

Also as some of the sockets in the trunking are on different trips should the earth terminals of the sockets all be bonded together.

Thanks

Carl

 

[NotHimAgain]

In a IT suite at a local school we have dado tunking with Cat5 and power in it. The sockets are wired on 20amp radials 3 or 4 sockets on each trip. They are wired in 2.5mm Low smoke single. We have had some sockets moved and they have been wired from the first socket on the radial (Low smoke connecting this socket to distribution board) in 2.5mm T&E with a 4mm bond cable between earth terminals on the new sockets.Am I right in thinking this wrong and should have been done in low smoke cable or is it going to be ok.

This introduces two topics: LSF (low smoke and fume) or maybe LSOH (low smoke zero halogen) and, circuits that may have high protective conductor currents.

LSF & LSOH
Why was this specified, is there a particular reason - if so it maybe essential to ensure all additions meet the same design criteria. If not it may not matter.

This can be a complex area and you would need to know the original design brief.

Is the containment system (dado trunking) LSF / LSOH?

You mention "T&E" is this PVCTWE or LSFTWE or something else?

High Protective Conductor Currents
IT equipment can give rise to high protective currents and this may require special measures (see section 543 of BS 7671).

Given your description of the installation - these currents may well exist and would have to be accommodated. You mention radial circuits but I am not sure what you mean by:

2.5mm T&E with a 4mm bond cable between earth terminals on the new sockets

and

Also as some of the sockets in the trunking are on different trips should the earth terminals of the sockets all be bonded together.

 

[carlday]

Hi

Thanks for the help. The sockets are wired in radial circuit from board to socket 1 to socket 2 to socket 3 then cable ends. The T&E used is PVCTWE and the single used is LSOH. The trunking looks as if it is standard trunking nothing on it that says it is low smoke.

thanks

Carl

 

[Chri5]

LSOH is a nice idea, but was the new bits spec'd (ask whoever issue the purchase order) as LSOH.

Unless specified most installers will provide generic TE cable.

On a side note, is the bonding / earth cabling LSOH- are the flexs on all the servers, fans, switches, hubs ?

Are the plastics in the cabinets, is the trunking, are the light fittings, the air con covers ?

I've worked in comms rooms and NOC's where every comms cable is LZOH, but pratically nothing else is and then the icing on the cake is that the gas / fire protection system is based on some of the most polluting gases known to man

 

[NotHimAgain]

If the trunking is normal PVC it will probably not be worth worrying about the cables inside it .

Various methods are available to provide for high protective conductor currents in radial circuits.

These include running a separate protective conductor from the last socket outlet back to the distribution board. This could be 4mm². Another method involves connecting the earth terminals on the last socket outlet on each radial to at least one of the other circuits.

The method used is a matter of choice for the installing contractor. They should also take into account any Electro Magnetic Compatibility (EMC) issues that could arise from the use of a particular method.

 

[carlday]

Thanks again.

Just another quick thought, the single cable cpc is 2.5mm the t&e cpc is 1.5mm, there is a 4mm earth connected to the earth of each the new sockets as well as the 1.5mm cpc. Is that good or bad? the cpc back to board is 2.5mm.

Carl

 

[NotHimAgain]

Well I am having to judge this from your description - from that I would say that the two cpcs are not required.

The fact that they are there does not introduce any particular safety issue - although some may have some concern about the termination of different sized conductors in the same terminal.

There could be an EMC issue, but if you have not suffered any problems with electro magnetic interference this is probably not a concern.

 

[carlday]

Hi

I thought that the 2 cpc's would not be needed. My only concern was is it ok dropping cpc size from 2.5mm (from board to socket 1) to 1.5mm (sockets 2 and 3). Would I be better not using the t&e cpc and running a seperate 2.5mm cpc.

Regards

Carl

 

[NotHimAgain]

Hi

I thought that the 2 cpc's would not be needed. My only concern was is it ok dropping cpc size from 2.5mm (from board to socket 1) to 1.5mm (sockets 2 and 3). Would I be better not using the t&e cpc and running a seperate 2.5mm cpc.

Regards

Carl

This post appears to indicate that you are modifying or extending this circuit yourself. Unless you have suitable qualifications and experienced I would have to advise against this action.

This installation is in a school so there could be a risk to children. In addition, a school is a work place and as such is within the scope of the Electricity at Work Regulations 1989 (Statutory).

 

[carlday]

Hi

I do have relevent qualifcations NVQ 3 in electrical installation and AM2 etc. I am going to correct it myself but I am letting the niceic contractors next week test it and inspect it. I was unsure as to the best course of action so I thought I would ask the forum. If it is ok it gets the lid put back on trunking and I need not get the contractors to touch it, if it needs changing i will do it and get them to test it. The reason I asked is the contractors or in on a day rate so the more i get them to do the better it is for the school so if at all possible I don't want to be wasting there time asking them questions.


Thanks

Carl

 

[NotHimAgain]

Well I glad to hear you have the qualifications - what about the experience?

On a more general note - if I were in your position I would not want to get involved in the detail of the contractor's work - you are exposing yourself to risk if anything goes wrong and you are giving them a "get out of jail free card".

 

[dannyboi2003]

Hey Guys,

OK i think this is getting a bit carried away now, if the new sockets have been installed by an approved contractor they will have been tested and certified accordingly and you will be supplied with the paperwork once all works are complete. Do not modify the wiring under any circumstances as you would render these tests as invalid, how the new and existing sockets have been wired sound just fine to me and id leave them well alone. Why low smoke cable was used i don't know, maybe the contractor had a large amount left over from a previous job and wanted to use it up or maybe it's more to do with where the cable runs once it leaves the trunking/room and runs to the distribution board.

I have seen dado trunking additions wired in a number of ways so what you describe does not sound uncommon.

As i said, leave it well alone as its in a school and any work should be carried out by qualified contractors with the appropriate test equipment.

All the best
Dan

 

[carlday]

HI

I think the sockets were installed by someone in the school. I found them when doing something else in the room and i was unsure if they were right hence the query. So big question is ok or not ok. I am still confused about the cpcs why have two and why use 4mm. I am going to get the contractors to have a look I think when they are in anyway.

All the it suites here are wired in low smoke for some reason.

My experience is in domestic wiring for 7 years and ac drives for 2, I now work in a school in ICT and I have the joy of PAT testing all the school.

Carl

 

[NotHimAgain]

If the sockets have been installed by someone in the school I would advise that you get them checked out by a contractor who has experience of this sort of work.

IMO work like this in a school or other work place is not within the realms of DIY and, whilst I accept that you have qualifications, you do not appear to have worked on this sort of circuit before.

There is guidance material available such as the On Site Guide, Guidance Notes 7 & 8 and Paul Cook's Commentary on the 16th Edition - you would also need a copy of BS 7671.

 

[carlday]

Hi

I agree and I am going to let the contractors sort it out. I have not had much experience in school/office enviroment thats why I was unsure what to do. I have learnt a bit today so thanks to everyone for their advice I shall read my shiny new 17th edition regs later and brush up a bit.

Regards

Carl