**CU Changes And YOU**

[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