A little help with 2 IR readings please

[lady electric]

Hi, i have a ring main with 6 sockets 32a breaker 2.5mm/1.5mmcpc for which i am getting a reading of 0.38 IR between L-E, how do i go about finding the fault
Also i have a shower 40a breaker 6mm/2.5cpc with a reading of 0.26 IR between L-N, how do i go about finding the fault.

This question is part of my assessment at college and any tips, offers of help would be very much appreciated
Thank you )

 

[malcolmsanford]

The normal fault finding method on a ring final circuit is split the ring. As this is a college assement I have to assume that all loads have been romoved. You would normally find the approx middle of the ring and remove the socket and divide the legs up into the 2 legs. You do another IR test and it will show you which leg the fault is on, you then just remove each socket and split the cables until you get the poor reading.

On the shower you would normally open the double pole switch and IR the cable from the CU to switch if that is OK. You then drop the switch and disconnect the shower and and test the cable from switch to shower, if that cable is OK you know it is the shower, are they wanting you to test the shower??

Must remember as this is an assement you must make sure you do everything by the book, safe isolation, checking the meter and probes for damage etc etc.

I have to ask those readings are really really low nearly a dead fault, you sure it is IR and not part of a ring continuity test or a R1 +R2.

 

[telectrix]

the 0.38, i assume is 0.38 Mohms. check all sockets for a possible faulf behind socket, trapped cable etc. check for junction boxes under floors. try and get a reading with the sockets pulled off the walls.

your 0.26 on the shower may well be the shower itself. to get an accurate reading you need to dis. the cable in the shower. also, it could be the neon in the shower switch.

 

[lady electric]

Hi Malcolm, thanks for your help - to answer your question i has readings of 0.5 as R1+R2 but rn was oc, does this make sense?

Thanks Telectrix, would the neon cause the reading to be so low?

Also if i have a faulty switch on a 2way circuit, do i try to identify and label ends to work out one of the cables as faulty?

 

[telectrix]

depends on if you're reading 0.26 Mohms or 0.26 ohms.

 

[telectrix]

if rn is o/c you will still read IR and also r1+r2. if this is college work, it's likely that a N has been dissed behing a socket.