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Topic Title: Extending existing circuits
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Created On: 20 June 2013 08:42 PM
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 20 June 2013 08:42 PM
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Ojf10000

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Hi guys, apologies if this topic has already been covered but I couldn't seem to find anything. Basically I'm wiring a small lounge extension for a customer. Majority of my work is new build so I must admit I'm not quite up to speed with requirements on extending a circuit. Due to the location of the CU it was impractical to install new circuits so have therefore extended the existing ring and lighting circuit. Tested existing circuits and they are sound on IR, cpc and ring continuity, loops etc. Sockets are already rcd protected (cu is split load 16th edition style). I will move lighting circuit to rcd side as my cables are concealed in walls. Earthing etc is all up to date. What I am unsure of is do I need to bring the entire circuit upto 17th edition requirements or just my new parts? There is nothing majorly wrong, things like no identification on switch lives, the odd socket with no grommet, solid green earth sleeving, the usual stuff you find in an older installation. I'm hoping I can leave existing parts alone and just note my findings in the 'comments on existing installation' section of the installation cert? Thanks for taking time to read my long winded essay :-) Any of your answers are greatly appreciated.
Cheers
Ollie
 20 June 2013 11:03 PM
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AJJewsbury

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Current regs only apply to new work - the only requirements on the existing installation is that it can support the new work (e.g. provide sufficient current carrying capacity, low enough Zs, equipotential zone etc) and isn't made dangerous by the changes.

There's certainly no requirement to bring existing up to current standards - otherwise you'd be ripping out perfectly sound cables just because they had red & black cores (or going around sleeving every termination) -which would be silly.

- Andy.
 21 June 2013 07:28 AM
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Ojf10000

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Thats great thanks andy. Am i correct in thinking I would need to list the non complying items on the cert then?

Cheers
Ollie
 21 June 2013 07:49 AM
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ebee

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There is an issue of "Wiring Matters" on this site that may be helpful to you:-

Spring 2009 issue 30 additions and alterations

http://electrical.theiet.org/wiring-matters/2009.cfm

I hope that helps

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 21 June 2013 09:58 AM
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Parsley

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Originally posted by: ebee

There is an issue of "Wiring Matters" on this site that may be helpful to you:-



Spring 2009 issue 30 additions and alterations



http://electrical.theiet.org/w...atters/2009.cfm



I hope that helps




The Wiring matters article seems to go against the ESC guidance. I could be reading the wiring matters article incorrectly it is Friday (see page 4) but it seems to suggest that the whole ring final circuit including concealed wiring must be 30ma RCD protected. The ESC guidance for a similar example is below.

Q2.3

A socket-outlet is to be added to an existing circuit. The work is not being carried out in a special location and the existing circuit has no RCD protection. The new socket-outlet is to be flush mounted 150 mm horizontally from an existing socket-outlet, and connected with wiring concealed in the wall. What is reasonably expected for the installer to do to comply with the 17th Edition?



A socket-outlet that is added to an existing circuit will need to have RCD protection (except for a socket-outlet designated for a particular item of equipment, such as a freezer).

In addition, if the wiring that is used to extend the existing circuit is concealed in the wall, then at least the extended part of the existing circuit will need to be suitably protected (by RCD or other means).


Regulation number(s)
411.3.3
522.6.101 to 522.6.103

Regards
 21 June 2013 10:17 AM
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ebee

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Yes I did think of pointing out, but decided against clouding the issue.

Mark Coles (IET senior engineer and well respected chappy) does appear at odds with most other opinions by insisting that in order to comply then the remainder of the existing circuit including the portion of it that you have not worked on, must comply with current regs along with circuit protection, meter tails, bonding & suppliers facility.

Futhermore, although circuits not worked on could be left as is (although you`d reasonably point out any concerns).
Works in a special location would involve all circuits of that location complying including circuits not worked on.

say you install a shower circuit in a bathroom then all existingcircuits in the bathroom must also be made to comply as well (RD on lighting etc etc) even if you had not intended to touch those circuits.
Of course I think we`d all install supp bonding unless the whole existing was up to current standards too.

Otherwise you could not sign off the cert of BS7671 compliance

At Elex Harrogate, after his article and his excellent forum , a few of us approached him because we thought we`d perhaps misunderstood those points about the remainder of existing circuits/special locations requiring complete current reg compliance but he confirmed it.

I know that some think he was being a tadd pedantic but if you read the regs they could be taken to mean exactly what he said.

Whether that was exactly the intention of the authors, well I think he would be in a better position than us to guess.

________________

Anyway , putting that aside for now, I think that article might help the OP

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 21 June 2013 10:46 AM
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Parsley

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There's an interesting CIBSE paper on touch voltages that highlights the potential issue of touch voltages in bathrooms where all the bathroom circuits are RCD protected and supplementary bonding has been omitted, but there are still other circuits elsewhere in the installation that are not RCD protected.

Regards
 21 June 2013 05:26 PM
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Ojf10000

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Thanks a lot for all your input. The wiring matters guide was a very interesting read. Who needs the pub on a Friday afternoon ey?!
Thanks again
Ollie
 03 July 2013 05:19 PM
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AJJewsbury

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I know that some think he was being a tadd pedantic but if you read the regs they could be taken to mean exactly what he said.

Ebee - do you know which regs in particular he was referring to? (I've re-read the article again and I still don't follow his reasoning).

I think the numbering has changed - where he refers to "110.1 - (xx) additions and alterations to installations and also parts of the existing installation affected by an addition or alteration" - I think that's now 110.1.2 (vi), but my copy seems to say that 'the regulations include requirements for ... alterations or additions' (which they do, 132.16 for one) - but that seems a long way from saying that the entire regulations are to be applied to existing.

I can see the logic that you might affect parts of the circuit that you hadn't worked on - e.g. by extending a ring you'd probably increase Zs at the rings mid-point, even if you were only working close to one end, and the effect of that would need to be taken into account; but that still doesn't seem the same to me as demanding that BS 7671 be applied retrospectively in full to the entire circuit.

- Andy.
 04 July 2013 08:01 AM
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ebee

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Andy,
off top of my head I`ve forgotten actual regs but I did have a read at the time and concluded that technically he was correct and I did wonder if the authors actually did not intend that but more in line with the way the ESC etc interpret it.

I`m a bit pushed for time next few days too otherwise I`d take another look/have another think.

Basically I think his point was if you add an otherwise compliant portion to a non compliant circuit then you can not sign off that your addition is compliant because compliance includes the circuit it is added to.
If you install a separate circuit then no problem (providing bonding etc are in place).
Exception being a special location, where the whole location must comply not just the circuit you install (IExample you install shower inc RCD & Supp bonding then RCD not on existing lighting etc means you do not sign off as your addition being compliant as it depends upon the remainder of the location).

Actually I can see the OMS scenario of fault on circuit prior to RCD in bathroom causing RCD not to mitigate bathroom cpc from raised voltage during earth fault - being applicable in this case to RCDing added part on a ring final say (your cpc in the added bit has a cpc dependant upon the OPD of the ring not the RCD under a existing ring fault)

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik

Edited: 04 July 2013 at 08:07 AM by ebee
 04 July 2013 08:56 AM
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Parsley

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Actually I can see the OMS scenario of fault on circuit prior to RCD in bathroom causing RCD not to mitigate bathroom cpc from raised voltage during earth fault - being applicable in this case to RCDing added part on a ring final say (your cpc in the added bit has a cpc dependant upon the OPD of the ring not the RCD under a existing ring fault)


In the cibse paper an earth fault is simulated outside the location on a non RCD protected circuit and the Ut measured in the bathroom between exposed & extraneous conductive parts with and without supplementary bonding in place.

With supp bonding Ut was <4V
Without supp bonding Ut was 64V

Regards
 04 July 2013 09:40 AM
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ebee

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Yes but the OMS scenario was a non RCD circuit (say lighting) then put in a local RCD to feed the bathroom portion of the circuit only.

An earth fault in the bathroom should trip within the RCD times. OK.

An earth fault say in a bedroom (before the RCD`d part of the circuit) would trip dependant upon the OPD for the circuit the RCD would not effect the disconnection time of the cpc in the bathroom .NOT OK.
Therefore supp bonding still a requirement.

-------------------------
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Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 04 July 2013 09:50 AM
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Parsley

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Same difference.

Regards
 04 July 2013 11:30 AM
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AJJewsbury

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Thanks ebee - don't worry, it's only idle curiosity on my part!

The bathroom bit is puzzling too - I could see that, given the 701 requirement that 'all circuits of the location need RCD protection' that you could argue that you need to comply with that for your small addition to comply ... but if the writers of the regs had that in mind, why do they still specify supp bonding and make its omission conditional on a stack of conditions that (most of at least) would automatically be satisfied if the entire location complies with up-to-date regs. They clearly seem to be considering situations where other parts of the location don't comply.

- Andy.
 04 July 2013 11:44 AM
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ebee

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Andy, I agree with you entirely.

Parsley, no it`s not the same difference.
In your example the 64V without supp bonds would still apply if the bathroom portion had an RCD that was fed from the remainder of the circuit with an earth fault upstream of that bathroom RCD

-------------------------
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Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 04 July 2013 04:17 PM
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Parsley

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Sorry Ebee, I'm not following you maybe I'm not reading your post correctly. RCD's won't stop the touch voltage they will only limit the time it is present, sup bonding will lower the touch voltage.

An installation original installed to 16th or earlier possibly with 5 sec disconnection times on some circuits. The bathroom gets a refit the spark installs local 30ma RCD's to protect the bathroom circuits only and decides to omit the sup bonding in the bathroom as the water is bonded at the incomer. An earth fault occurs external to the bathroom on a circuit with 5 secs disconnection time, without the sup bonding there could be problems in the bathroom whilst the protective device warms up, if sup bonding was in place the Ut will not be an issue.

Regards

Edited: 04 July 2013 at 04:32 PM by Parsley
 04 July 2013 04:43 PM
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ebee

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Exactly,
The RCD will not limit the time for the fault to clear , only the OPD does that ( unless such fault occurs in the bathroom)
So supp bond must not be omitted.
RCD or not makes no difference in this particular scenario.

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 04 July 2013 05:21 PM
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AJJewsbury

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So supp bond must not be omitted.

Arguably you can get a similar situation with a fully confirming 17th Ed installation - circuits outside the bathroom (>32A or distribution circuits) are allowed 5s (or 1s) disconnection times and can transfer a potential into the bathroom through metal pipework. Main bonding all extraneous conductive parts doesn't guarantee <50V touch voltages within the bathroom - yet we're told that supp bonding may be omitted in that case. Another case of best practice and the letter of BS 7671 not being completely harmonised?

(Personally, I prefer plastic pipework for bathrooms!)

- Andy.
 05 July 2013 08:55 AM
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Parsley

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The 16th had 413-02-13 to cover mixed disconnection time issues.

Table 41C was also useful too.

Regards
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