**CU Changes And YOU**

[ukpablo]

i think mike2790 is referring to the pre test at the CU mentioned by the OP (or soft test as it has been called between neutral and Earth bar at 250V) to determine if any faults are present before doing any work on CU changes.

 

[malcolmsanford]

i think mike2790 is referring to the pre test at the CU mentioned by the OP (or soft test as it has been called between neutral and Earth bar at 250V) to determine if any faults are present before doing any work on CU changes.

So why is it not legitimate?

 

[ukpablo]

im not saying an IR test is not legitimate, just does not state the test between Neutral and Earth bar at CU as a pre test prior to a CU change in GN3 or BS 7671. This is something that was pointed out as a thing u may want to do by the OP. Thats the way i read it anyhow?!
i see what u are saying malcomsford and im not stating that u are wrong either, im just reading between the lines on this thread????!

 

[mike2790]

So why is it not legitimate?

as chiplard has stated above, IR tests should be performed at 500v unless it is not practical to disconnect all loads. obviously in a domestic dwelling 99% of the time it IS practical to disconnect all loads to enable a 500v IR test, so in this instance a 250v IR test would not be legitimate. the section of the regs you pointed out does highlight that a 250v test IS ok if there is an item of equipment which is not practical to disconnect, but ONLY that circuit, so all others have to be tested at 500v. you missed the point a little bit with what i was getting at anyway but i do realise the good book is open to a lot of interpretation. just tell me whether you would pass your 2391 or any other exam which involves testing at some point if you IR test at 250v? the 250v test described in this thread is just a quick test on neutral and earth which will give you an idea whether or not the fancy new rcd board will trip like a hippie on acid, turning your few hour board change into an all nighter lifting floor boards.

 

[malcolmsanford]

Mike I don't take the view that what your saying is not in good practice correct, what I'm saying is that when you use words such as legitimate then it conveys that the 250v Test is not right.

I fully agree in an initial verication there can be no excuse for not doing a full 500v DC test across LIVE/LIVE and then LIVES/EARTH. But the post was for a board change and therefore literally either a full or semi PIR on the existing installation.

I don't know about you but I would indeed, unless I was truely concerned with the installation, just do a 250v LIVES/EARTH only test and see what that got me. If I had a poor result then I would indeed do each circuit individually again at 250v LIVES/EARTH until I found which was giving me that poor reading, Then look at the individual circuit more closely. If I got good results then I would indeed do the 500V test but again only LIVES/EARTH

I always found that the regs as a guide was invaluable, but it gives scope for thought and interpretation. I know as a competant person if I was changing a CU on an installation that was 50 yrs old perhpas even wired in VIR that I would be doing a lot more testing before I fitted the board than a 10 yr old installation that had no obvious signs of tampering, Each installation would though both be tested to ensure that they were safe and still in a condition to be used, it would just mean different levels and perhpas even different ways of testing.

To just say that someting is not legitimate conveys that it must never be done, and I'm sorry that is wrong. I will not comment on the way individulas are trained, but fortunately I was trained to think and to assess, which to me is what a competant person is.

Please don't think I'm carping at you, as I said at the start your not incorrect for an initial verication every time, but on a PIR and so a board change, you are giving scope by the BS 7671-2008 to assess the installation.

 

[nickblake]

Actually a 250 volt is a legitimate test especially when doing PIR's i will never carry out a PIR and do an straight IR test at 500 volts and i was taught many years ago not to , the reason is simple if for any reason there is still an appliance plugged in boiler washing machine PIR's even a sub board with an RCD main switch the chances of blowing these up are very high and could be very costly , so an initial test of 250 volts followed by a test at 500 volts if the installation is clear and mark it down on the Certs even omitting the LN test by shorting out theL and N and testing that between earth and noting this down on the certs it is a acceptable way of testing , totally agree with malcome comments

 

[mike2790]

Actually a 250 volt is a legitimate test especially when doing PIR's i will never carry out a PIR and do an straight IR test at 500 volts and i was taught many years ago not to , the reason is simple if for any reason there is still an appliance plugged in boiler washing machine PIR's even a sub board with an RCD main switch the chances of blowing these up are very high and could be very costly

actually, did you not even read my post? i never said just test at 500v and fingers crossed nothing blows up, quite the opposite. this threads turned a little bit ----for-tat and a bit boring too. however i feel that testing each circuit fully is the best way to go. just a quick question to you and malcolm, do you do a full test cert for a board change? and if so what do you record as r1 or r1+r2? because in a lot of instances you would need to disconnect loads at the furthest point of each circuit to obtain a reading, for example a shower circuit. the only reason i ask this is that if your disconnecting the loads, why not test at 500v anyway? also the term 'competant person' is the reason a lot of us 'time served' electricians are struggling to find work, but thats for another thread i suppose.

 

[malcolmsanford]

I assume Mike your meaning R1 + R2 as your talking about a shower circuit and not a ring final circuit. Yes when I do an EIC fora new installation or an addition, I do the R1 +R2 on it, as I think it is a better than the R2 only test, which I'm quite entitled to do on an EIC, and on a CU change I might just do that on a lighting circuit if there are outside lights on PIR that I don't want to start taking apart. On a PIR I have often just done an R2 only espicially on hi bay warehouse lighting. Again as the tester I deem what tests are necessary.

I really don't know where this is going, In fact after this post I do think you need some refreshing on testing. It's R1 + R2 on a shower or any other circuit,you only do r1 rn and r2 on a ring final circuit. Also you just not only do a r1 test,there is no such recognised test, I think your meanig R2 but then I'm not sure what you mean.

I'm disputing you term legitimate. Now we can bat this about as much as you wish, IMO you using the term not legitmate when referring to a 250V test is not true, it is a perfectly Legitimate test.

It is completely irrelevant if you consider it legitimate or not, that is quite rightly your opinion on it. But you can not advise others that it is not a legitmate test when in the guide we adhere to advises it is.

A lot of us time served electricians do a 250 volt LIVES/EARTH test before we even start on a CU change, it is often used as a guide, and I would be quite within my rights to do that only test and put it on the EIC if I wanted to, as it is not a departure from the regulations. I'm sure like me the majority of us do also do a 500 volt test after, if we feel it warrents it and it is not likely to damage anything. After all I'm not going to go around an entire installation disconnecting everthing, possibly taking out 30 or 40 down light lamps, disconnecting transformers, PIR or dimmers, unless I found a problem.

 

[mike2790]

I really don't know where this is going, In fact after this post I do think you need some refreshing on testing.

why would i need refreshing? and who are you to say so? my qualifications are as good as any. we're merely trading opinions. people like you who get so ---- about things are the reason a lot of people avoid posting on sites such as this. this image springs to mind.

 

[nickblake]

Sorry mate didnt mean to offend and yes i did read your post i just wanted to express my opinion and belive you me i do a full circuit test drives my apprentice nuts and i will re do a test to i will never cut corners , my real point was that in some circumstances you could miss an item boiler etc with one of those nasty hidden away sockets behind cupboards etc with the years of doing inspections i have see almost every thing , when i test an R1R2 of say a lighting circuit i test at every point till i get the highest reading at the end of the circuit and the reason for this is beacause i got caught out a few years ago when i did a test R1 R2 insulation and Zs all tested fine but what i hadnt spotted was that the polarity changed half way down the circuit and then changed back again so you wouldnt spot it so im a swine when i test now , as for the competant and time served sparks struggling for work , i sympathise with those who are struggling ,but when you have the 3 week wonders and the 10 minuit PIR guys doing 6 PIR 's in a day this is where they need to stop it

again please accept my appologies if i offended you ,as i do take our trade very seriousley

Nick

 

[mike2790]

but when you have the 3 week wonders and the 10 minuit PIR guys doing 6 PIR 's in a day this is where they need to stop it

or the one hour board change brigade!

cheers nick

 

[Spudnik]

Change the record fellas,

I didnt start this for it to become another qualification vs experience bashing thread.

 

[nickblake]

Sorry jason wasnt my intention ,ive change the record and im listening to when im cleaning windows

 

[Lioned]

Hi. when doing a CU change is it an absolute requirement to upgrade the tails to 25mm.Got a job where the meters outside and tails 16mm go up cavity in a conduit,not enough room to get 2 x 25mm up there.
Can upgrade earth to 16mm but no way get new tails up.Its a 60 amp cut out so ok for 16mm,but if i use this one for my assessment is it going to be ok if i reconnect with the existing 16mm tails ?
Thanks.

 

[malcolmsanford]

The OSG does advise the tails being 25mm now, (see pg 17 section 2.2.3) but ultimately it is the DNO that will decide what tail sizes they want as it is their fuse that is supplying fault protection.

As the Fuse is 60 amp then keeping the 16mm tails will be ok, what it will mean though is that the DNO would not upgrade to a 80amp most likely and definately not a 100amp.

As it is an assement just advise the assessor that the protection device is 60amps and as the customer did not want to the extra cost and disruption that would have been caused by trying to fit 25mm ones, and that should be that. Remember your being assesssed to be a cash cow, he will not fail you if you explain the logic behind doing something.