New build insulation resistance

lincoln sparks · Jan 9, 2012

Hi, first post on here and interested in your views on this. I have just second fixed two 4 bed houses and have some less than perfect results on the insulation resistance tests on most circuits. I'm aware of the minimum requirement in the regs is 1 meg but anything less than off the scale worries me! I think the problem is with damp as have split rings etc to check for faults and even took off some sockets to dry them out, which i think proved the damp issue being present. I dont normally do new builds, most of my work is re-wires , entensions and have never had readings like this.
So a question for you fellas who do a lot of new builds is this a common problem ?

needasparks · Jan 9, 2012

Can be a problem with damp as you say with new plaster, it can also be an issue if cables were installed when it was too cold on site as pvc does not like being moved at near 0deg's that we had not that long ago and may crack the insulation letting damp get in.
As this was new build i take it that the site had a roof ect so rain the like did not add to problem and now sealed the water in as T&E will absorb water if expossed to it.
Way of check if damp is the issue is pump the IR to 1k for 30 secs and watch to see if it drops during that time while it drys for the test.

EDIT

Welcome to the site. BTW

Engineer54 · Jan 10, 2012

lincoln sparks said:
Hi, first post on here and interested in your views on this. I have just second fixed two 4 bed houses and have some less than perfect results on the insulation resistance tests on most circuits. I'm aware of the minimum requirement in the regs is 1 meg but anything less than off the scale worries me! I think the problem is with damp as have split rings etc to check for faults and even took off some sockets to dry them out, which i think proved the damp issue being present. I dont normally do new builds, most of my work is re-wires , entensions and have never had readings like this.
So a question for you fellas who do a lot of new builds is this a common problem ?

Come on, ....Tell us what IR your getting on these insulation tests??

Deleted member 26818 · Jan 10, 2012

One way to tell if it's damp, without taking things apart, is to prolong the test, and see if the reading climbs.

Lighthouse Phil · Jan 10, 2012

What were the readings you were getting????
Often seen IR as low as 1 meg ohm on new installs......
what were you getting?

How long were you leaving the meter on the circuit?

Richard Burns · Jan 10, 2012

I had 8Mohm on one new install, but I installed while it was raining, two days later >1000Mohm

kamkam · Jan 10, 2012

Had the same on a new build last year readings where all over the shop... came back a few days later and all good

so in my case it was 100% damp

lincoln sparks · Jan 10, 2012

Thanks for all replies and yes I forgot to state the readings. The lowest readings were around 10 meg and although these did climb when I kept my finger on the button of my test meter. I tested the circuits at first just before christmas and to be fair the house was pretty damp, condensation everywhere. At the time I dis-connected a number of sockets and then connected them up as a mini ring with a few scraps of 2.5. I then tested my make shift test rig and it was same poor result. I then dried out sockets at home and the following morning the results were perfect, 200 plus. I then returned to site, re-connected and re-tested and as time went on the readings went down. I've been back today using fan heaters and so on to try and get a decent reading for the certificate, which I achieved. Some interesting replies and very helpful too, cheers to all of you.