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.

 

[Octopus]

If you join all 4 ends together, by which I conclude you mean the ends of the live and neutral there's no wonder you get a 0.00 IR!

 

[telectrix]

yep. for IR testing, you need all the ends separating as you are measuring the integrity of the insulation. if you short the conductors out, you will read 0.

 

[i=p/u]

i asked my tudor about doing 2391 while i was doing level 3 and he steered me away

 

[olsonn]

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

 

[telectrix]

separate all ends. set meter to 500V. clip on L/ N. press test button. repeat for L/E and N/E. make sure nothing is plugged in first or be prepared to fork out for new pc, TV, etc.

 

[i=p/u]

just connect single cables like radial l-n,l-e,n-e its all continuous

 

[Des 56]

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

Would you care to give a step by step account of your procedure, so that comment can be made on your procedure, rather than people saying what should be done

 

[olsonn]

Not a problem Des. I carried out the 3 step continuity test and results were as expected ie: r1 + rn/4 and r1+r2/4. Then to do the IR test I used one end of the ring cable and connected my clips to the Line an Neutral, with the CPC cables unconnected. The other end of the cable was unconnected, with none of the conductors touching. As a precaution I always test at 250v first, a lesson I have learnt from this forum. When I tried to test, I got a reading of 0.00.

 

[telectrix]

it would appear that he's trying to perform an IR test with the conductors linked as for continuity.

 

[Electricalserv]

Simple...


Unplug all appliances and loads. test between the mcb screw terminal & neutral bar. Repeat between mcb screw terminal & earth bar.record results........ Simple your ring I/R test

 

[timo1]

Try youtube and type in insulation resistance there is a good vid on there which will make it easy for you.

 

[telectrix]

Simple...


Unplug all appliances and loads. test between the mcb screw terminal & neutral bar. Repeat between mcb screw terminal & earth bar.record results........ Simple your ring I/R test

and what about N/E ???

 

[Electricalserv]

and what about N/E ???

Plus N/E only reason I didn't say because it doesn't need recording!

 

[SirKit Breaker]

I will try to make it simple.

Disconnect BOTH legs Line/Neutral and earth, of the ring circuit from the Consumer unit.
Keep the legs seperate from each other.
Keep all the individual cores seperate from each other, so all conductors are not in contact with any of the others.
Now connect your meter to L and N on one end of the circuit, test
Repeat L and E
Repeat N and E

Test complete, it is just the same method as for a radial circuit, but you have 2 ends, so watch out that you dont touch the opposite end to the one you are testing on as it will energise with the Insulation resistance test voltage.

Hope this clears the air a bit for you. Buy Guidance note 3 if you haven't already got it, this shows step by step all the required test procedures with full instructions, and pictures, it is the testing bible.

Cheers.........Howard

 

[telectrix]

it does on my castline certs.

 

[Electricalserv]

If the resistance between L/N are o.k and also between L/E you can edge your bets N/E will be aswell!

 

[ezzzekiel]

most certs also

 

[Octopus]

separate all ends. set meter to 500V. clip on L/ N. press test button. repeat for L/E and N/E. make sure nothing is plugged in first or be prepared to fork out for new pc, TV, etc.

If you've got any doubt that there may be stuff still plugged in I'd recommend that you test at 250v before moving on to 500v

 

[telectrix]

If the resistance between L/N are o.k and also between L/E you can edge your bets N/E will be aswell!

you hope. if no loads connected, L/N will read good. L/E will also read good even if you short N/E

 

[topquark]

If the resistance between L/N are o.k and also between L/E you can edge your bets N/E will be aswell!

Cobblers, well known for making shoes.

 

[Electricalserv]

Cobblers, well known for making shoes.

Thanks mate :49:hahaha. pardon my french that comment was rubbish. If anything its more likely going to be a fault between either L/E & N/E

 

[telectrix]

earth leakage faults are always between L/E or N/E.

 

[topquark]

Thanks mate :49:hahaha. pardon my french that comment was rubbish. If anything its more likely going to be a fault between either L/E & N/E

Quit digging the hole

 

[telectrix]

well, there i was , diggin that hole , hole in the ground, so big and round and deep it was. it's not there now, the ground's all flat, and beneath it is the bloke in the bowler hat. ( good place for LABC )

 

[olsonn]

Well I took the advice offered and disconnected both ends of the ring at the board. Put the L N and CPC from one end in to seperate choc blocks and tested using the other end. Tested between N and CPC and got 9.06, then tested between L and CPC and got 9.06 not great but a pass. Problem is I tested between L and N and got 0.00.


What am I doing wrong, or am I doing right and the circuit is wrong??

 

[telectrix]

are you sure that there are no loads connected, FCUs with neons, someting plugged in?????

 

[topquark]

Well I took the advice offered and disconnected both ends of the ring at the board. Put the L N and CPC from one end in to seperate choc blocks and tested using the other end. Tested between N and CPC and got 9.06, then tested between L and CPC and got 9.06 not great but a pass. Problem is I tested between L and N and got 0.00.


What am I doing wrong, or am I doing right and the circuit is wrong??

9.06 What? Megohms?

 

[olsonn]

Yes Megohms

 

[Benn]

This is what I do......

First make sure all appliances are unplugged, any fuse spurs turned off (this would give you a 0.26ish result, from reading between the neon)

One crocodile clip on both live conductors, the other on the Neutral conductors. Test. Hopefully >99.9

Repeat test for Live/Earth and Neutral/Earth.

Done. Although you could save time, by doing as what someone said above, using the screw in the MCB, and the busbars. If your really special you can IR test the whole installation at once. Making extra sure, you disconnect any equipment suspect to high voltages.

 

[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!