insulation resistance testing bombshell

[brav]

i agree mate, but what do we do, what we believe is right or whats in the book?

 

[diabalo]

Very interesting thread. First hats off to the Doctor for his humility and the other members for a lively debate. Not an electrician myself but had a CU change at home recently, mainly for the benefit of modern levels of protection. I did buy an OSG in preparation so that I was up to speed with the process and to assess how compliant my house is and what if anything might show up in the preliminary EICR. I noticed that the insulation resistance tests shown in the OSG are all described and illustrated with the cpcs connected and that the term "earth" and "at the distribution board" are used. As a layman if I were following the testing process as described I would not have disconnected the cpc. When adding in an additional circuit I noticed that the electrician tested the new cables before and after connection. This seems to me as a customer an indication of thoroughness even if he could have got away with a global test at the the end. Delighted with the result - full rcbo board, well worth the investment.

Very grateful to everyone on here for sharing their knowledge.

 

[steptoe]

whats with the head banging?i would do the same, but there are inspection and testing books now sayng there is no need to remove the main bonding conductor when testing an exsiting installation, ie EICR

If the worst happens as like the OP's sineario and we end up in front of a lawyer with these books in front of us going through all the tests we did, i would have said i disconnected the main bonding to take a measurement and he/she would show me a book based on BS7671 saying i shouldnt.

what are you calling the main bonding conductor?

exactly, merely based on a non statutory document, I know 90% of domestic work is carried out to non statutory documents, but as Zee rightly says, how do you know the readings you are getting are from that actual cable otherwise?

the cable may go to a pipe, which is then bonded via the boiler to another cpc, etc.

 

[loopdog]

In your scenario though, you mention that there was a leak at a later date. This leak would not be present during the testing so would not show up in IR test. Particularly if the metal stud wall was sat on wooden floor boards.

Loops

 

[sparkatus1]

I learned this lesson at an early stage of my testing career. I meggered the cable for a particular circuit and all was clear yet I couldn't get the rcbo to stay on. Eventually after a bit of head scratching I tested N to Earth bar. Turned out somebody had burned the cable so bad the neutral was touching the basket that had been installed.

 

[the doctor]

Hi All,

I note that the subject is now covered in the middle paragraph on p39 in the new guidance note three.... :Applaud

Trust you are all well...

 

[wozz]

So in the instance doc is talking about on page one, the rcd didn't work? Or am I missing something?

And what's the resistance of concrete? The word 'may' was used, do walls shot into concrete have any connection to earth?