old CU needs upgrading.


Postby jaffa19 » Sun Sep 07, 2008 9:53 pm

[quote="mephistico"]Bear in mind also that the bonding may be undersized to current regs & a test/inspection is probably due.
With an older installation there is no need to comple with 17th edition regulations. You should concentrate on getting it up to 16th edition (split load board, sockets on RCD 10mm main bonds, supplementary earthing etc)[/quote]

Are you sure you mean that??

I thought that ALL work carried out after the 1 July 2008 MUST comply with BS 7671:2008 to carry out work only to 16th edition regs (although benifical) would be incorrect advise ?? I believed that this person wanted to carry out major works, thereby changing the installation requirements.
:o
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Postby ericmark » Mon Sep 08, 2008 10:20 am

Thank you jaffa19 I had missed mephistico comments

“Bear in mind also that the bonding may be undersized to current regs & a test/inspection is probably due.”
This is true and often there is no earth connection where original bonding was in bare copper and very small and has been broken long ago and I have seen electricians fail to remove bonding to water pipes etc. before testing so giving completely wrong results this is dealt with in the IET/IEE wiring maters summer 08 issue 27 available for down load off web site.
”With an older installation there is no need to comply with 17th edition regulations. You should concentrate on getting it up to 16th edition (split load board, sockets on RCD 10mm main bonds, supplementary earthing etc)”
Once anything is updated, then that must comply with 17th if designed after 31st June. It is causing major problems where minor works are completed and they need RCD protection at the origin due to buried wires. As to split load boards either double or triple one can’t just fit and assume it will comply.
“314.2 Separate circuits shall be provided for parts of the installation which need to be separately controlled, in such a way that those circuits are not affected by the failure of other circuits, and due account shall be taken of the consequences of the operation of any single protective device.”
So if combining the down stairs sockets and up stairs lights on the same RCD or visa versa when a fault occurs on a socket and one can’t see ones way to the consumer unit it would contravene the regulations but if there were wall lights running off socket supply so there would still be light to see ones way to consumer unit it would not the same applies if emergency lights are used. 314-01-01 and “314-01-02 A separate circuit shall be provided for each part of the installation which needs to be separately controlled for compliance with the Regulations or otherwise to prevent danger, so that such circuits remain energised in the event of failure of any other circuit of the installation, and due account shall be taken of the consequences of the operation of any single protective device.” of the old 16th Edition regulations were very similar in their wording and one does need to consider if the regulation was ever any different or have we been interpreting wrong over the last 16 years?
Eric
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Postby s1bgs » Fri Sep 26, 2008 3:24 pm

Am i right in saying that if I update my CU I will then have to test all circuits, continuity, ring, Ins resistance, earth loop impedence and so on.
I know all bonding is correct size and that it is a TN-S.
just need to be sure.
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Postby TOPSPARK » Fri Sep 26, 2008 6:40 pm

If you change your consumer unit then all tests as stated in BS7671 must be carried out as it is considered you have changed the parameters of the existing circuits so the testing is of paramount importance and all results recorded on an electrical installation certificate along with the schedule of inspections and schedule of test results pages.
regards
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Postby ericmark » Fri Sep 26, 2008 8:34 pm

As an electrician I would test all circuits twice. Once before I start to ensure there are no faults that are likely to cause problems with RCD’s after the change. This would include insulation test and supply earth loop impedance and earth loop impedance on a local socket but not everything.
After or during the change I would test items like ring main continuity etc. It is surprising how many faults one uncovers I have found ring mains being fed from two fuses so on 60 amp rather than 32 amp.
But I would not do a complete PIR in that I would only test a few sockets with earth loop impedance tester and I would not as a matter of course remove all sockets to inspect.
If I found an error I may go further for example we know the line loop resistance when checking for a ring on a 2.5mm ring main should be no more than 0.72 ohms was 0.6 ohms and earth loop of 1.2 ohms was 0.95 ohms should we find that it is above this limit then we may either just note or if authorised look further as to why.
The 4% volt drop has been increased to 5% volt drop hence old and new values.
You are going to have to fill in an installation certificate which will include a Form 4 Schedule of test results you are not required to do a test twice and you can use inquiry, calculation or measurement. With a ring main we often take end to end reading, and some forms allow you to enter these reading direct, instead of R1 + R2 or R2 or Earth loop impedance only one is required. But all measurements are required like a full PIR it is only some of the inspection that can be skipped.
It is rare to be able to do a full inspection and test there is normally something in the way. For example in my house there is a radiator in front of a socket so impossible to test.
One thing to check for is borrowed neutrals on stairs lighting. It was common to borrow a live on two way switching so three core and earth was not required and this will trip RCD if lighting is split up and down stairs.
Eric
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