lighting circuit problem

[deroeper]

just rewiring a down stairs lighting circuit its all wall lights had faults all over the place on the existing wiring so decided to rewire all apart from kitchen lights .
it was all wired in 1mm so have changed it to 1.5mm all circuits are in jb's
and i have sitting room lights dining room lights landing light and kitchen now the kitchen is still in the 1mm wiring .
At each jb have done a IR test on each circuit before connecting all togeather all fine however when i connect the sitting room lights i get a reading of around 800mohms .
yet take it off feed all ok checked the mains feed and that is ok.
I am stumped could it be the old cable (1mm) thats giving me silly results (bearing in mind tested on own its fine) i am kinda chasing a ghost ! any idears.
using a Metrel tester .

 

[deroeper]

Things you need to let us know, what tester are you using, what are the I/R test results before connecting living room lights, P/N P/E E/N for each, and after connection, also what are your continuity readings, any reason for leaving the 1mm kitchen lighting circuit, did you wire the drop downs to the wall lights, and switches.
if you think the cable to the living room light might be damaged, i would change that section. We await your response.

Its a metrel easy test i am getting >1000 IR on all tests on individual junction box connections i.e living room, landing lights sitting room and kitchen now i connect them all to mains feed (which is also >1000) and i am in the clear except when i connect the dining room lights , which on there own gives me >1000 but connected the whole circuit drops to around the 800's . I havnt done the kitchen because of access problems , even though it is comming up >1000 . I cant find a leak anywhere its a neutral earth problem , and as i said everything is new apart from kitchen, would the old 1mm cable to the kitchen be giving me hassle when loaded with the rest of the circuit??
Oh and all wiring has been changed 1.5 down to wall lights as well

 

[telectrix]

mt MFT reads >99Mohms. that's good enough for me.

 

[Martin Bradley]

No problems with circuit, the reading is super.
Series and parallel

 

[deroeper]

I am a little confused (but i am blonde) > 1000 on my meter means there is no connection , its like holding the leads in the air , yes
surely if i have a reading in the 800's i have a leakage somewhere? dunno i have never put down on my sheets anything other than >1000 am i being dumb can someone explain??

 

[Martin Bradley]

Are you winding us up, have a look in your regs book what does it say about min value that is Acceptable, as this is exissting instalation
all values you have quoted are fine, even for a new installation.

you just need to be a bit more confident in your work.

 

[deroeper]

chapter 61 table 61 up to 500v >1.0..... i took it my Metrel >1000 is 1.0 ?

 

[telectrix]

think your metrel>1000 means >1000 meg. no tester will say > 1.0meg.

 

[deroeper]

this tester i dont use much only use when meggar off for re cal i dont think i any very confident with its readings!
you kinda get used to one!!!

 

[pushrod]

If you test 5 separate bits of a circuit and each says > 1000 MΩ it doesn't mean that when you connect them all together you still expect greater than 1000MΩ.

The longer a circuit is the lower the insulation resistance readings becomes as there will be more "micro leaks" of current along the greater length.

I wish all my problems were at 800 MΩ - my tester doesn't even read that high lol

 

[Martin Bradley]

Dielectric breakdown little holes in the pvc, its all good, the lower the reading the less resistance in the material pvc.

 

[deroeper]

Well thanks all going to do kitchen wiring as well , once i can get in, then test again, hopefully get a better reading!!!
And i will be more confident, Bradley, next time as long as i am over 1.0 i wont give a dam!!
i wrote that wwrong!

 

[tony mc]

I would as 1 Meg is a fail GN3 states the minimum reading is 2 Meg .

Like I posted before the more ccts you add the IR can go down even with heathty ccts.

1/RT = 1/r1 =+ 1/r2 that should jog your memory

 

[pushrod]

I would as 1 Meg is a fail GN3 states the minimum reading is 2 Meg .

Like I posted before the more ccts you add the IR can go down even with heathty ccts.

1/RT = 1/r1 =+ 1/r2 that should jog your memory

An insulation of not less than 1 MΩ complies. A 2MΩ reading indicates a possible latent fault and should be investigated.

I think the 2 MΩ figure is the min IR reading for fire alarms circuits.

 

[tony mc]

Thanks Pushrod I should of worded the reply better.

If someone tests and its just over 1 M ohm they need to be doing something about it not just recording and leaving it, at the very least documenting the low reading on the EIC making sure the customer is aware of a possible latent fault on the circuit.