odd insulation resistance test results

[islowey]

I have a simple one way lighting circuit that serves one fluroescent tube. there is a single jb up in the roof. now when tested here i get a reading of >1999 Mohms for the insulation resistance test on the individual cables. but when connecte together i get 376Mohms at the junction box and 30MOhms at the CCU all for the same circuit! i want to energise this but am a bt worried as i cant visually see anything wrong and the individual cables test fine ... any ideas ?

cheers
ian

 

[WarrenG]

If I understand you correctly, it sounds to me that when you are testing at the JB and the CU with the cables connected you are leaving the light switch closed (i.e ON) giving you the reading you are getting.

You should disconnect flurescent lights, neons, dimmers switches, electronic timers etc to perform this test without damage. (500V!)

For lighting, if it is inpracticable to remove all lamps (say you have 40 flurescents) the local switch controlling the equipment may be left in the off position.

Try testing again with the swich in th off position.

Hope this helps

Warren.

 

[2391bob]

what you need to do is check your r1+r2 first, maybe that is the real reason why your I.R.test result figures were so high.i.e.>1999Mohms.also concur with previous poster,disconnnect (and make safe)fluorescent fitting.

 

[islowey]

Many thanks for the replys
I did a ri+r2 reading which was normal and also tested the IR wiht the fluro disconnected totaly, the circuit was open (bar the switch being on)
hmm its not a huge issue as the 376Mohm reading is well above 7671 guidelines
still it would be nice to know exactly why

cheers
Ian

 

[hughesy]

Many thanks for the replys
I did a ri+r2 reading which was normal and also tested the IR wiht the fluro disconnected totaly, the circuit was open (bar the switch being on)
hmm its not a huge issue as the 376Mohm reading is well above 7671 guidelines
still it would be nice to know exactly why

cheers
Ian

Hi mate i just had exactly the same problem but with differant circumstances i wired a new build house then it was left for aages and when i did my second fix my ir on my s/o tested only 36MEG so i tryed to find the fault but couldnt find one so i tested each piece of cable individually and they all cleared 1000MEG OHM yet when i tested the ring fully connected i got only 36MEG and found out this was down to damp in the cable so i turned on the power and it was fine came back a few days later to retest and got >1000MEG OHM so the wiring had dried out .wasnt the best building site i have worked on lol.

 

[fusion]

energize it pal it will be safe..trust me..

 

[harrymonkfish]

Hi there.

Could someone please explain the reading I get from my insulation resistance meter. I'm doing 2330.

I set up a simple circuit at home. t&e to a socket. Not connected to the house wiring in any way.


when I carry out the test I get '>1000M ohms (with a pass tick)'

this is the maximum value of the tester. does this mean the insulation is top notch?

in my frustration i decided to create a fault in the insulation. i took a stanley knife and striped the insulation from all the conductors half way down. re-tested and got the same result.

Have I got the wrong end of the stick?

please help.

thanks
harry

 

[Spudnik]

Hi there.

Could someone please explain the reading I get from my insulation resistance meter. I'm doing 2330.

I set up a simple circuit at home. t&e to a socket. Not connected to the house wiring in any way.


when I carry out the test I get '>1000M ohms (with a pass tick)'

this is the maximum value of the tester. does this mean the insulation is top notch?

in my frustration i decided to create a fault in the insulation. i took a stanley knife and striped the insulation from all the conductors half way down. re-tested and got the same result.

Have I got the wrong end of the stick?

please help.

thanks
harry

There has been all sorts of debate about this.

A couple of examples.

A person performed the same test as you and got the same results.

I recently part rewired a property for student acommodation (ring and showers etc) but not the lighting.

I IR tested the lighting and had a perfect reading, however, i installed a new shower circuit and had to go into the loft.

Whilst i was in there, looked across and saw, what must have been, about 3 meters of insulation chewed from the lighting T&E.

SO, in essence an IR test is not always conclusive on small sections of cable rather it is on a long circuit (lighting etc) maybe.

 

[fusion]

first of all mate make sure the jb connector screws are clean and very tight.then test again first..& then check the earth for parallell paths..

 

[harrymonkfish]

Thanks for that jasons6930
.


But is the reading of >1000M ohms correct? Does that mean the cable passed the test with flying colors?

All the connections are tight. I re-wired it to make sure.

many thanks

harry