How to wire cpc in class rooms

[bs7671]

Hi there my question is if you were installing a final circuit in a computer room for IT purposes,how would you wire the c.p.c.I think maybe it is something to do with a switchmode something or two earths???I have looked but cannot find anything specific to answer this.Help appreiciated thanks guys n gals

 

[telectrix]

unless it is specifically stated that earth free sockets are required, I would wire them normally. What do others think

 

[djb_1983]

The NIC told us that for IT equipment and areas using computers you need to use sockets with two earth terminals and connect each cpc seperately. Also at the distribution board the two cpc's from your ring need to be terminated in seperate terminals on earth bar. Not sure what reg number was tho.

 

[bs7671]

djb_1983 good answer but where else could I find out the infomation from a formal source

 

[djb_1983]

There are diagrams in on site guide with relation to this , from memory im not too sure what page its on. Hope that is of help to you.

 

[Spudnik]

543.7.2.1

which relates back to 543.7.1

 

[Deleted member 9648]

It is because of the potential for high earth leakage on IT equipment....the regs are to ensure that each outlet will maintain a cpc connection even if one cpc becomes disconnected. The cpc's must be run as a ring whether the circuit is a ring or radial and each cpc must be connected to a separate terminal at each socket and at the DB.

 

[jeremy]

Just throwing one in here but if the earth positions are already marked by manufacturer, and the rest are full how do you do seperate earths in CU. Crimping makes the 2 ends " one conductor" ( I think). Could they then go into the same point on the earth bar?

 

[telectrix]

excellent answer, wirepuller. clarified the post exactly. as to jeremy's post, wouldn't it be a good idea for CU manufacturers to add a couple of extra holes in the earth bar, for this very purpose?

 

[Sintra]

What you are permitted to do is this.

CPC 1 from circuit 1 in terminal 1 along with CPC 1 from circuit 2
CPC 2 from circuit 1 in terminal 2 along with CPC 2 from circuit 2 etc etc.
Using this method takes up no extra ways on terminal block. This is only acceptable if the CPC's are all marked with their correct circuit number and the cu is labeled accordingly.

 

[jeremy]

excellent answer, wirepuller. clarified the post exactly. as to jeremy's post, wouldn't it be a good idea for CU manufacturers to add a couple of extra holes in the earth bar, for this very purpose?

You're right, it would!! but what are the chances?

 

[telectrix]

and, whatever happened to the removable earth link so one could split the main earth to get Ze. only reason i can think of is if some careless sod left it off, but same careless sod could leave the earth cable out. either way would show up when Zs readings were taken

 

[jeremy]

What you are permitted to do is this.

CPC 1 from circuit 1 in terminal 1 along with CPC 1 from circuit 2
CPC 2 from circuit 1 in terminal 2 along with CPC 2 from circuit 2 etc etc.
Using this method takes up no extra ways on terminal block. This is only acceptable if the CPC's are all marked with their correct circuit number and the cu is labeled accordingly.

i can see the reasoning behind it but it seems a bit trusting of those following?

 

[Sintra]

As long as the guy following is competent enough to know about high integrity earthing then there shouldn't be a problem. If he isn't competent he shouldn't be near it.

 

[Deleted member 9648]

I can see this becoming a general requirement in the forseeable.....the justification being the ever increasing use of IT equipment in the home......probably worded 'any circuit supplying socket outlets which may reasonably be expected to supply an item of IT equipment'....which of course would mean an amendment...all buy another regs book,guidance notes,courses......DOH!

 

[Darkwood]

What you are permitted to do is this.

CPC 1 from circuit 1 in terminal 1 along with CPC 1 from circuit 2
CPC 2 from circuit 1 in terminal 2 along with CPC 2 from circuit 2 etc etc.
Using this method takes up no extra ways on terminal block. This is only acceptable if the CPC's are all marked with their correct circuit number and the cu is labeled accordingly.

Ive honestly never heard this method may i ask where you got this from, although i understand it and how it avoids lost earth but see that it contravenes other regulations concerning termination position and seperation of terminated circuits, ive always had to add an additional earth bar for these purposes with the Niceic man saying this is the only acceptable way.... please enlighten me im interested where this method comes from.

 

[andyb]

Ive honestly never heard this method may i ask where you got this from, although i understand it and how it avoids lost earth but see that it contravenes other regulations concerning termination position and seperation of terminated circuits, ive always had to add an additional earth bar for these purposes with the Niceic man saying this is the only acceptable way.... please enlighten me im interested where this method comes from.

It's all down to interpretation of the regs, the niceic inspector told me this method & so it's the method I use.
Obviously the cpcs & the board need clear labeling but it makes sense to me.

 

[Sintra]

Ive honestly never heard this method may i ask where you got this from, although i understand it and how it avoids lost earth but see that it contravenes other regulations concerning termination position and seperation of terminated circuits, ive always had to add an additional earth bar for these purposes with the Niceic man saying this is the only acceptable way.... please enlighten me im interested where this method comes from.

Ok it complies with reg 543.7.1.4 & reg 543.7.1.5 regarding seperate terminations of the cpc and labelling.

Reg 514.1.2 States "As far as is reasonably practicle wiring shall be so arranged or marked that it can be identified for inspection, testing, repair or alteration of the installation"

So if the method i use is labelled correctly it also complies to the above reg.

I in the past have also used an additiional bar and would be my prefered method but on occasions have used the alternative one bar method.

NICEIC inspector disputed the one bar method on an assessment a few years back and when i pointed out that it complied to the regs he agreed.

 

[Darkwood]

Well it sounds like its tried and tested, but would enquire how you would mark this up then if for arguments sake rings are in circuit 4 and 5 then earth for circuit 4 will be tagged with 4's and circuit 5 with 5's respectively, now the earth bar is fixed with markings 1 to ......whatever, if you put earths 4 and 5 in terminal 4; earths 5 and 4 in terminal 5 then you have in my mind clearly made a termination that is in itself confusing to anyone following you, having an earth no'5 in terminal 4 is where i think it dosnt comply as you have a conflict of markings, please give me your thoughts as i do understand the reg's can sometimes be interpreted in different ways.
I totally understand that the board will be marked with label for high current earth etc but im asking around and no-one in my circle of sparkies has heard this so surely if its a little known method its likely to confuse others and ive yet to see this method in any onsite guides in picture form at least but maybe this is where i eat humble pie and you direct me to the guide and page.
Please dont get me wrong im not trying to prove you wrong im trying to understand where this method comes from as i dont like doing anything im not 100% certain about as i like to be as good as i can be i dont do things because im allowed to do thing i do things because i understand why i do them.

 

[andyb]

It probably isn't in any guide Darkwood, it's just a method of complying if there is no extra earth bar in the board.
As for identification, I use those little numbered rings that you can buy from the wholesaler & slip them over the earth sleeving.

 

[Darkwood]

It probably isn't in any guide Darkwood, it's just a method of complying if there is no extra earth bar in the board.
As for identification, I use those little numbered rings that you can buy from the wholesaler & slip them over the earth sleeving.

I too use the number rings but the point i was putting across if you re-read my last post was you will have an earth from each ring marked up and in confliction to the earth terminal it is in this invitably will lead to confusion for even a competent electrician following as this method isnt widely practiced to my knowledge, this in itself i feel dosn't meet with the reg's although it will meet reg's regarding earth seperation for the high earth current circuits.

 

[jimes]

doesnt the cpc have to be bigger with high earth leak equipment? cant remeber exact numbers.....

 

[Sintra]

No 1.5mm as in a T&E is fine in a ring.

 

[Sintra]

Well it sounds like its tried and tested, but would enquire how you would mark this up then if for arguments sake rings are in circuit 4 and 5 then earth for circuit 4 will be tagged with 4's and circuit 5 with 5's respectively, now the earth bar is fixed with markings 1 to ......whatever, if you put earths 4 and 5 in terminal 4; earths 5 and 4 in terminal 5 then you have in my mind clearly made a termination that is in itself confusing to anyone following you, having an earth no'5 in terminal 4 is where i think it dosnt comply as you have a conflict of markings, please give me your thoughts as i do understand the reg's can sometimes be interpreted in different ways.
I totally understand that the board will be marked with label for high current earth etc but im asking around and no-one in my circle of sparkies has heard this so surely if its a little known method its likely to confuse others and ive yet to see this method in any onsite guides in picture form at least but maybe this is where i eat humble pie and you direct me to the guide and page.
Please dont get me wrong im not trying to prove you wrong im trying to understand where this method comes from as i dont like doing anything im not 100% certain about as i like to be as good as i can be i dont do things because im allowed to do thing i do things because i understand why i do them.

Have a look at this guide from the iet.

View attachment High Integrity Earthing.PDF

 

[Darkwood]

Have a look at this guide from the iet.

View attachment 2491

Thx for the info' Sintra this is what i couldnt find myself but having read it im happy the method is acceptable and if i employ this method at least im now confident in its use, but reading the pdf you linked it does state that large dist' boards may come with many spare terminals, where some manufacturers may supply an accessory kit to add extra way, [where this is NOT an option, the following solution is one method].......thus the earth cross-over method is explained.
My interpretation of this is that an accessory kit needs to be fitted if you are short of spare earth terminations and only when this is not an option that it is one method to get around this problem, so i can see it been used in older dist' boards when installing new high earth circuits and spare ways or accessory kits are not available but if the board is been changed i would think a suitable board should be chosen and not relying on this method as routine.
Appreciate the feed back thanks..

 

[Darkwood]

doesnt the cpc have to be bigger with high earth leak equipment? cant remeber exact numbers.....

Its dependent on the expected mA leakage to earth if you look at the pdf Sintra sent me further down it explains when larger earth may be needed, this is also why you need to limit the number of sockets on a computer ring main:-
1. so you dont exceed the mA permitted for the smaller cpc arrangement.
2. rcd coverage would also become prone to tripping if too many computer points were wired on one ring.

 

[Sintra]

Thx for the info' Sintra this is what i couldnt find myself but having read it im happy the method is acceptable and if i employ this method at least im now confident in its use, but reading the pdf you linked it does state that large dist' boards may come with many spare terminals, where some manufacturers may supply an accessory kit to add extra way, [where this is NOT an option, the following solution is one method].......thus the earth cross-over method is explained.
My interpretation of this is that an accessory kit needs to be fitted if you are short of spare earth terminations and only when this is not an option that it is one method to get around this problem, so i can see it been used in older dist' boards when installing new high earth circuits and spare ways or accessory kits are not available but if the board is been changed i would think a suitable board should be chosen and not relying on this method as routine.
Appreciate the feed back thanks..

Agree 100% i have only used the method in an insulated cu where there is no possibility of an additional bar etc.