Help IR Testing on a ring final circuit

[olsonn]

I am trying to do some individual circuit testing ahead of my 2391 practical, but I am having a problem with final ring circuits. Radial circuits aren't a problem, but when you look in all the guidance including GN3 it only deals with lighting circuits. Do you have to join all 4 live ends together? I am obviously doing something wrong as the 3 step continuity of ring final circuits is, spot on as is the R1+R2, but I am getting 0.00 for IR.

 

[alanl]

9M ohms?
That is a poor reading.
I've only come across such a low reading in the last year on a 1940's house with original wiring.
I know anything over 1M passes, but I'd be looking to see what is causing such a low reading if it is on any modern (<20yrs old) installation.
If you are doing 2391, surely you have had some experience and should know how to do these tests?
If not, then I think you'd better do a lot of reading and practical testing, as Insulation testing is pretty basic.
HTH
Alan.

 

[olsonn]

Alan

I think the problem lies with the circuit rather than the test approach. I am going to have to split the ring up tomorrow to see if I can find what is causing the problem. It is going to take some time as there are no installation diagrams etc so I know the ring starts and ends at the board, but god knows how it has been routed. Don't really see any options other than lifting floorboards to trace the cable. obviously something wrong with a 0.00 L to N reading and the other two may be passes but worry me. Every socket is empty so nothing there causing the problems.

 

[telectrix]

bear in mind there may be FCU's on boiler, aerial amp in attic, hidden socket behind a fridge or behind kitchen base units, FCU for cooker hood hidden behind the flue.

 

[olsonn]

One of these days I must work on a newbuild where you know where everything is because you put it in. But then again it wouln't be half as much fun as trying to find the neddle in the haystack or the look on the customers face when you ask if they have any paper work for the installation

 

[nickblake]

All i will say is when you do ring insulation tests get some 2 way lever wago's and put them on the return leg of the ring one on L one on N and one on the CPC saves getting zapped by a flying return leg or easier still joint the 2 lives together 2 neutrals together and test each one between the cpc never fly into an insulation test i always test at 250 volts first then test at 500 volts if there is sensitive equipment in circuit then you stand less chance of blowing it up

 

[Goody]

obviously from the responses so fa,r I am doing it wrong, but what nobody has siad is how I should be doing it

There are some useful videos here -> Insulation ResistanceTesting

 

[olsonn]

Thanks everybody for you help on this, finally found the route cause of the problem, an FCU behind the bed for an outside light, now getting greater that 500 megohms on all tests

 

[telectrix]

there you go then. a valuable lesson learnt."if in doubt, pull it out", or was that birth control advice?

 

[Mr Mike]

Well done olsonn. Next time you will not be caught out like that again, a good lesson.
There is always an answer....

 

[Goody]

Thanks everybody for you help on this, finally found the route cause of the problem, an FCU behind the bed for an outside light, now getting greater that 500 megohms on all tests

Thank you, for sharing your findings!

 

[the pict]

Or the meters on Cont getting a open circuit response

 

[Zorro]

Don't forget precautions and preconditions before Insulation Resistance testing.