**CU Changes And YOU**

[Spudnik]

No reason not to use 500V.

 

[Ohmyword]

Not certain if this is the correct Thread for this question/query - but to quote a statement from the "Regs Thread" :- Meter tails are part of the consumers installation and are to be provided by the installer. Meter tails must be sheathed and insulated or if insulated only must be enclosed in trunking or conduit. Meter tails must be 25mm.
Is that last sentence applicable to every mains distribution board in the U.K? (As a minimum size I assume?)
I know of one electricity supply co. with it's own meter fixers who only use (max.) 16.0 m.m. tails from cut-out (main service fuse) to meter. This is in West Cornwall area.

 

[mandrews]

previously over the years i have mounted ccu's on an mdf board.
with cut out on the back of ccu and mdf board,
for cables to enter,
I have seen NICEIC testing inspection dvd with Tony Cable saying its a fire risk to have a hole in the mounting board...




Attatched are photos of two diffrent NICEIC domestic installers 17th edition boards taken of google images
with the mounting board and an opening to show what i mean.


the only regulation i can find close to what i need to know is.


BS 7671 134.1.6


Electrical equipment likely to cause high temperature or electric arcs shall be placed or guarded so as to minimize the risk of ignition of flammable materials.


does this mean if the wooden cut out is larger then the opening on the back of ccu this would reduce if not stop any sparks coming into contact with mounting board and would meet all requirements to BS 7671

 

[Jas0n7]

Because if you have bad readings Earth to Neutral then you might have problems with RCD's holdinig in.

 

[gpz900jim]

maybe its to rule out neutral to earth faults which would not show themselves up until the rcd was switched on

 

[1billy wiz]

if you get an earth to neutral fault will the reading be under 2meg??

& if your only testing the consumer is that just the tails???

thank's in advance to any comment's

 

[WDMDL]

If you get a neutral to earth fault, the reading you get will depend on the nature of the fault.
Trapped or interconnected neutrals to earths will always show up as zero megohms.
Anything under 2 Megohms obviously needs looking into - but in a domestic situation something under 2 meg but not a dead short will generally be quite obvious... starting with that steamed-up outside light!

One good reason for testing at 250V is so you don't have to chase all around the house looking for surge-protected extension leads. The active elements (Metal Oxide Varistors) fitted in these start to conduct above a nominal 275Vrms or 369Vdc - typically they will pass 1mA once the voltage has reached about 400Vdc

The majors like pinched neutrals in metal boxes will still show up, as will those in the high tens of Megohms such as from bad kitchen installations where there is plaster and tile adhesive touching the socket terminal screws.

Of course when you do your full tests you'd have to unplug everything to test at the proper 500V... the purpose here is "to get a feel for the the place" before you commit yourself.

And what will 500V show up that 250V didn't?
One example is insulation damage, where a conductor is very close to another as a result - it will arc across under test, showing as a reading which ramps up towards the hundreds of megohms, then abruptly falls right down then ramps up again.

Another is tracking - where something has gone BANG and deposited a metallic film on the internals of an accessory - these can go conductive particularly when damp. These tend to show up as an unsteady insulation test reading, wavering rather than the abrupt fall as above.
Simon.

 

[thekingiam]

hi Jason S
very useful post as this is what i am going to do as my first job my brother has two CCUs one split load one wylex fuseboard and it was done by a so called electrician. the new ccu is split load half protected half not. i either want to swap the circuits from fuseboard to new CCU but will have to install RCBOs on non protected side.I also notices that the so called electrician had upgraded gas bond but not the water which is only 6mm on a P.M.E system and looks as though the insulation has been melting so not good.or i will install a completley new CCU to the regs and install 10mm to the water.The main cut out fuse has been taken out as there is no seals. I will have to notify LABC as i am only just setting up and not registered yet with governing body as i am going to use this as my major install for registration is it ok for me to pull main fuse to accomplish this i know supplier should but as the seals are missing anyway would i get away with this as far as building control go sorry for taking up the space but new to all this

 

[thekingiam]

i posted this above again from the begining of this thread by another user as i am in a similar position and i couldn't find a response.

 

[brucelee]

Hi thekingiam

thought i thought i was seeing things it was i who posted what you after finding out matey

 

[TPES]

Hi Jason

I found out some very handy info from 'DurhamSparky' on here, and I am sure he wont mind me passing it on, regarding changing a CU and non earthed lighting ciircuits.
The crux of it was that al lighting and switchgear needs to be changed to class 2 and a label needs to be applied to the new CU stating that the lighting circuit is not earthed and that no metal fixtures can be applied to it.
If the customer does not agree to the changes in their fixtures then a sparky is advised not to go ahead with the CU change.

Hope that helps.

Old thread I know..

Just wondering what your thoughts are if the customer does not want to change a few of metal light fittings in the house (all plastic light switches)

But they want you to change there old rewireable fuse board.

Would you all walk away from the job and not change to a new CU?

 

[Des 56]

Here is the guidance and no,I would not walk away
You cant force people to be sensible and spend money, but you can advize and still stay in work

http://www.esc.org.uk/pdfs/business-and-community/electrical-industry/BPG1v2_web.pdf

 

[TPES]

I have read the many different guides and unless I'm reading them wrong they say "do not proceed with CU change"

So if the customer doesn't want the disruption of running cpc's to the lights and doesn't want to change his metal fittings what would you do to cover yourself when issuing cert.

A spark I know said he's not leaving the installation in any worse condition than before he started, puts a warning label on CU about having no cpc's to lights and and issues a "potentially dangerous condition notice" and comments on the EIC..

This makes sense I think, but then there are sparks who will follow what's written in guides and walk away from the CU change.

 

[Des 56]

The esc guide doesn't stop you doing the cons unit
It tells you that if they refuse the upgrade, but still want the consumer unit, then you carry out a risk assessment
If it was me,my risk assessment would be to have a look at the location of the class 1 fittings, for proximity to nearby piework etc, and test the fittings to ensure they are good insulation values to the metalic parts of the fitting,then between those parts to the pipework
Advize the customer the best bet is upgrade the circuit
If they refuse
Take into account the test + inspection of the fittings,put a warning label at the cons unit about the lack of cpc and plonk all the information on the eic then do the job and get paid

 

[TPES]

Take into account the test + inspection of the fittings,put a warning label at the cons unit about the lack of cpc and plonk all the information on the eic then do the job and get paid

With having no CPC for the lighting circuit how would you fill in your results for the "schedule of test results" on that circuit? eg, Continuity, Zs, RCD...?

N/A?

 

[Spudnik]

Basically yes.

 

[james king]

3 - Quick Basic Check & Tests

i) If convenient, isolate supply and take off the CU cover
ii) Evidence of additions or alterations?
iii) Carry out IR test between Earthing bar & Neutral bar at 250V


iii what does that test for? and what test results should u get? >299??? if 0.00 would this mean dead short? and also would it mean borrowed nutruals?

 

[TPES]

It's funny no one knows how to respond to that! I keep going write something then have to delete it

 

[ukpablo]

>299 is an open cct which is what u would ideally be lookin for, anything less tan 2Mohm would mean that a possible fault exists on one of the ccts, investigation req. (i would only do this at 250 v on my megger which would give u >99 Mohms)

Borrowed neutrals could only be identified by checking each neutral against each other unless i am wrong. 0.00 would mean a short across neutral to earth and this would ping the rcd when the new board is replaced. Further investigation by removing 1 neutral at a time could identify which cct it is on.

 

[domestic spark]

Now, if there are issues with an installation that are not considered unsafe, although not to current BS, (unearthed lighting circuits excluded), you ARE NOT generally required to put these right, although they should be noted on the cert in the correct box.

whatdo you mean by this, thanks

 

[nickblake]

Basically means that if you carry out a cu upgrade with say a lighting circuit with no cpc then you'd mark it on the electrical installation cert one thing you would have to do is the bonding to the services gas water etc , in the case of no cpc's you must mark the Cu to prevent people installing metal clad class 1 face plates and fittings

 

[domestic spark]

Basically means that if you carry out a cu upgrade with say a lighting circuit with no cpc then you'd mark it on the electrical installation cert one thing you would have to do is the bonding to the services gas water etc , in the case of no cpc's you must mark the Cu to prevent people installing metal clad class 1 face plates and fittings

so you cant condem an installation (lighting circuit) for having no earth)??? or any other circuit?


would this be because, wiring is old and work would have not been done to 16, 17th ed etc!! (dependant on age est)

or because there are no metal fittings?

if you were doing a PIR what code would this be??

with/ and without metal fittings.?

 

[lloyd1980]

A great thread BTW

I have glanced at this as about to price for a CU change
Just a quick one, domestic 30ma RCBO . Will trip when there is a 30ma imbalance between the line and neutral conductors

If I was to do an IR test at 500V dc between neutral and earth prior to install;

0.00 would indicate a short and would then indicate definate fault once installed

my question is this, if your Ir readings are low but above 1M ohm ( min ac ceptable reading )

at what point would the RBCO start to register a fault???? eg if the IR reading are low 2.6Mohm or in region of this fig, would an acceptable IR reading still trip the RCBO?

obviously its not a short but its showing signs of deterioration - at what point would the RCBO trip, when there is a short only????
I have known RCBO's to trip without there being a short, just preasure faults where conductors are kinked as been stuffed behind accesories.

just wondering does anyone have a definative answer to this
Thanks

 

[tedy]

A great thread BTW

I have glanced at this as about to price for a CU change
Just a quick one, domestic 30ma RCBO . Will trip when there is a 30ma imbalance between the line and neutral conductors

If I was to do an IR test at 500V dc between neutral and earth prior to install;

0.00 would indicate a short and would then indicate definate fault once installed

my question is this, if your Ir readings are low but above 1M ohm ( min ac ceptable reading )

at what point would the RBCO start to register a fault???? eg if the IR reading are low 2.6Mohm or in region of this fig, would an acceptable IR reading still trip the RCBO?

obviously its not a short but its showing signs of deterioration - at what point would the RCBO trip, when there is a short only????
I have known RCBO's to trip without there being a short, just preasure faults where conductors are kinked as been stuffed behind accesories.

just wondering does anyone have a definative answer to this
Thanks

I'm new here, but I think the tripping point when "the RBCO start to register a fault" is not so much related with IR (isolation resistance) but very much in relation with the csa of the cable, it's length, and it's impedance Zs.
Basically the RCBO is "watching" fluctuations of the current in cable, and in between cables

I don''t think you will find an definitive answer to your question, like a precise value ... because this varies with the length of the and CSA in principal.

And lastly, we have 30 mAmps, 100 mAmps and other, to clearly show us that is the (MAXIMUM) variation of the current in between the wires at tripping moment. (this is my own supposition)

 

[rryles]

A great thread BTW

I have glanced at this as about to price for a CU change
Just a quick one, domestic 30ma RCBO . Will trip when there is a 30ma imbalance between the line and neutral conductors

If I was to do an IR test at 500V dc between neutral and earth prior to install;

0.00 would indicate a short and would then indicate definate fault once installed

my question is this, if your Ir readings are low but above 1M ohm ( min ac ceptable reading )

at what point would the RBCO start to register a fault???? eg if the IR reading are low 2.6Mohm or in region of this fig, would an acceptable IR reading still trip the RCBO?

obviously its not a short but its showing signs of deterioration - at what point would the RCBO trip, when there is a short only????
I have known RCBO's to trip without there being a short, just preasure faults where conductors are kinked as been stuffed behind accesories.

just wondering does anyone have a definative answer to this
Thanks

To trip the RCD part of a 30mA RCBO will require at least 15mA of fault current. This corresponds to an IR reading of less than 15.3K. If the fault is Neutral-Earth then it will take an even lower resistance before the RCD trips (As Neutral-Earth voltage should be a small fraction of 230V).

So if you get an IR > 1M, then this is a long way off tripping a 30mA RCD (including RCBO).

 

[i=p/u]

good thread , if doing any work on any circuit, i thought was ok to IR test at 250v between l-n, n-e, l-e as this would save you removing all elements and sensitive equipment.and getting more than 2Mohms is this ok????

 

[nickblake]

you will find that even testing at 250 volts you will get low IR reading due to the resistance of the load , the easiest way to carry out thi test is to short out the L and N then test to the cpc and mark that that test has been carried out this way you are unlikly to damage any sensitive equipment etc , especially will all the low voltage transformers,pir fans etc , if i can unplug and disconnect every thing i will and test that way but doing that you may have neons in the circuit which may well cause false readings

 

[saabuldin]

you will find that even testing at 250 volts you will get low IR reading due to the resistance of the load , the easiest way to carry out thi test is to short out the L and N then test to the cpc and mark that that test has been carried out this way you are unlikly to damage any sensitive equipment etc , especially will all the low voltage transformers,pir fans etc , if i can unplug and disconnect every thing i will and test that way but doing that you may have neons in the circuit which may well cause false readings

When shorting L and N and doing IR test between L+N and earth. Can this test be done using 500v or do you have to stick with 240v.

 

[Lioned]

Hi ,have tried to read back and ,unless i've missed it,cant see it yet.When changing CU then its a must to upgrade main earth connection to 16mm,but what about main bonding to water and gas ?
Quite often you will find some kind of earth to the water but maybe only 4 or 6 mm or smaller ! If you cannot reasonably get a new 10mm to the water can you just leave as is but advise should be done and code 4 ?

 

[clark]

Please could you clear up the earth and neutral IR query and test to be done at just 250v.

 

[chiplard]

Please could you clear up the earth and neutral IR query and test to be done at just 250v.

It should be carried out at 500v. Table 61, P158 of the BRB unless it is reasonably unpractical to disconnect equipment.

 

[rryles]

Hi ,have tried to read back and ,unless i've missed it,cant see it yet.When changing CU then its a must to upgrade main earth connection to 16mm,but what about main bonding to water and gas ?
Quite often you will find some kind of earth to the water but maybe only 4 or 6 mm or smaller ! If you cannot reasonably get a new 10mm to the water can you just leave as is but advise should be done and code 4 ?

Codes are for PIRs not EICs. There is however the section on the EIC for "departures from BS7671". However, as I understand it, earthing and bonding is the one thing that must be brought up to current regs for any work that you do - no exceptions.

 

[malcolmsanford]

Regulation 131.8 is the guide for earthing and bonding on alterations or installations

Then capter 54 for the set of regulations.

 

[mike2790]

Please could you clear up the earth and neutral IR query and test to be done at just 250v.

insulation tests at 250v is not a legitimate test, this is only done to give yourself peace of mind that you arent going to run into all sorts of faults which a residual current device will detect, ie faults which were already present in the installation which a fuse or a 60898 mcb etc would not have previously detected.
also....
a 30mA rcd has a maximum allowance leakage of 30mA before it will trip. in reality a ramp test will tell you at exactly what leakage that specific rcd/rcbo will trip at. i usually find between 23-27mA is the norm. this is not a required test and is done in addition to the required rcd tests and is done again to give peace of mind that the device not only complies but is also not too sensitive.

 

[malcolmsanford]

insulation tests at 250v is not a legitimate test, this is only done to give yourself peace of mind that you arent going to run into all sorts of faults which a residual current device will detect, ie faults which were already present in the installation which a fuse or a 60898 mcb etc would not have previously detected.
also....
a 30mA rcd has a maximum allowance leakage of 30mA before it will trip. in reality a ramp test will tell you at exactly what leakage that specific rcd/rcbo will trip at. i usually find between 23-27mA is the norm. this is not a required test and is done in addition to the required rcd tests and is done again to give peace of mind that the device not only complies but is also not too sensitive.

I do realise that the BS 7671-2008 is not a statutory document and so therefore technically every test in it is not legally binding.

As the tests and testing procedures, as stated in this and the GN 3 is industry recognised as being "legitimate" why do you consider IR to regulation 612.3.2 not therefore legitimate. Can we assume that the whole of section 612 to be the same?

 

[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.