Ir tests

[huntos33]

Just testing a 3 bed house i've re wired, its a empty property totaly gutted and re furbed Re plastered etc... Just doing my IR Tests on my rings and getting results around 129 meg at 500v nothing connected anywhere and no neons etc, Should i expect to be getting >500 as with all other curcuits ive tested?. Just seems odd to me these are lower than the rest

 

[telectrix]

damp plaster? anyway 129Meg. is a well good reading. don't worry.

 

[huntos33]

damp plaster? anyway 129Meg. is a well good reading. don't worry.

Wondered about damp, thanks telectrix

 

[SirKit Breaker]

I always Con checked and IR tested the cable when it was new and still on the drum before i used it just to be on the safe side. Never found owt wrong, but never say never.
But i wouldnt worry, although you would expect the meter to go off the scale, 129 is still good, and as Tel says, probably damp.

Cheers............Howard

 

[Farmelectrics]

Re test in a couple of days and compare results

 

[Landril]

Check all connections are tight and have a good amount of conductor in the terminal, this can sometimes lower your reading.

 

[Jimmy Boy]

To the OP, you state a rewire..may I ask the test method you are using and where abouts you are placing your testing probes/croc clips in relation to the circuits in question ?

J

 

[telectrix]

i would hope he's clipping to the bare ends of the stripped conductors.

 

[Jimmy Boy]

i would hope he's clipping to the bare ends of the stripped conductors.

Well Tel great minds lol..I was just wondering if he was buzzing it from the incomer on the bus bar or even the N/L out on the RCBO both can throw a wobbler on an IR

J

 

[telectrix]

yep. IR testing is for the circuit/s alone. should never IR test with RCDs or any other sensitive equipment connected.

 

[Jimmy Boy]

yep. IR testing is for the circuit/s alone. should never IR test with RCDs or any other sensitive equipment connected.

Well unless your doing a PIR of course..Test method 2..

J

 

[telectrix]

agreed.

 

[WayneL]

i would hope he's clipping to the bare ends of the stripped conductors.

yep. IR testing is for the circuit/s alone. should never IR test with RCDs or any other sensitive equipment connected.

A bit tricky if your doing it by the book:

The insulation resistance measured with the test voltages indicated in Table 61 shall be considered satisfactory if the main switch board and each distribution circuit tested seperately, with all it's final circuits connected but with current using equipment disconnected, has an insulation resistance not less than the appropriate value given in table 61.

 

[Jimmy Boy]

The problem with that is it's guidance, prior to everything being RCD'd or RCBO'd pretty much in a domestic you could on a new install IR from the new tails if it was all >200 no drama, if you got an iffy reading split the circuits up find the problem, not so easy now with the current set ups, the other thing of course is the regs cover all scope of works, many of which don't have any RCD protection !

J

 

[WayneL]

It still remains that everything should be terminated before IR testing - so you couldn't go on the bare ends of stripped conductors.

Bearing in mind the regs have only just been ammended, you'ld think they'ld have altered the above regulation (sorry, 'guidance'), if it was a problem.

In the 2391 I went on the outgoing side of the RCD (i.e. the buzz bar) without any issues.

The problem you've got is, if you do as you(jimmyboy) and telectrix suggest, by testing each circuit seperately and disconnected from the CU, you could still have issues between circuits.

I'll just give you a very quick example so you know what I'm on about :

Conduit install, you IR test L-N on a socket radial, (disconnected from board) - 500v >299 M everything rosy.

Unknown to you, though, the 'line' conductor you've just tested is shorting out to the neutral of a lighting circuit (within the conduit).
It won't be picked up because you had the socket radial circuit's conductors out of the board.

The same thing can apply to CPCs - you IR test L-CPC with the conductors disconnected from the board - >299...........but what if the 'line' conductor has been snagged on some earthed metalwork somewhere - again, it's not gonna show up.

This is the reason you test with all conductors terminated.
If you have sensitive equipment in circuits, then, as the regs state, you have to compromise some of the testing, but the fact remains you should IR test as much of the installation in it's finished (terminated) condition as possible.

 

[oldtimer]

Did you split the ring and then retest as 2 radials ?

 

[WayneL]

Did you split the ring and then retest as 2 radials ?

For what purpose? - That goes against everything I've just said.

Sorry, just realised which part of the thread you're replying to - we're back on the fault finding:smiley2:

 

[oldtimer]

Well old school says split the ring in the middle and test no a big job but it pins it down so 12 sockets on a ring cut it to 6 then 3 now you know what area you are looking at plus if its the live that is showing a lower reading then its just the live you break at each socket

 

[1shortcircuit]

I've had a couple of issues with brand new MK sockets recently. IR's the circuit and results were lower than expected, split the circuit and pin point to faulty new socket:thumbsup

 

[Landril]

The same thing can apply to CPCs - you IR test L-CPC with the conductors disconnected from the board - >299...........but what if the 'line' conductor has been snagged on some earthed metalwork somewhere - again, it's not gonna show up.

Surely if the Line conductor was snagged on the CPC/Earthed metalwork there would be an extremely low reading due to the fact no insulation is between the conductors and they are forming a circuit!!!! Technicaly giving you a R1+R2 reading??