Sorry another post on IR testing!! Advice Please

[T&Earth]

Hi Everyone

Replaced out side light (Class 1 ) fitted new (Class 2) took 15 mins then spent 60 mins testing! This was because consumer unit in cupboard at the top near ceiling very difficult get to it. My question is can you do a IR test at the light instead of having to take the CU apart? My other point is I hate doing IR tests as I never get the results I expect! except when testing new work, which often makes me think I've missed a neon of someother thing that is thats giving me a low reading my read was 55M ohms which I know passes but I woul have liked it higher. I hve recently had on as low as 8M ohms on both occasions the customer had equipment which could not be turned off for long.

If someone could me some tips on IR testing and advice I'll be very greatful

Many Thanks

Steve

 

[Sparky Ninja]

The common expectation of getting results like >299 megaohm etc should only be expected with new installations. If you get readings like that on existing installations then fine. Great. Good.

On a typical installation the cabling will degrade over time, it's inevitable. We try to install to prevent derating and hence, degrading. However it is inevitable. When you carry out an insulation test, first assess the conditions.. temperature? moisture? excessive DIY? age? the existing system and wiring reference methods? Then carry out the IR test and start to understand how the numbers relate to the conditions. Then ask yourself if you are satisfied with your readings. Obviously something like 0.0 would mean you have a short and have likely left a load in. But readings like 8 megaohms etc are perfectly acceptable if you can justify to yourself a reason as to why this is your reading.

There is a big difference between knowing what readings you normally get and are allowed, than understanding why you have those readings and what physical attributes have contributed towards them.

 

[malcolmsanford]

The problem is if you test back from an appliance you will IR all the circuits on that CU as you have the EARTH/NEUTRAL commoned on their respective bar, so you will be upluging, bypassing and disconnecting everything in the house. Nothing is every easy is it so the best way to do it is disconnect from the board.

Unfortuantely unlike a PIR your MIEWC does want you to test L-N L-E and N-E and the only way really is to disconnect the circuit from the CU.

As Widdler said on old PVC unlike today's all singing all dancing PVC the insulation will degrade and you are unlikley ever to get the same results as with a new installtion.

On a PIR you can carry out tests you feel are appropiate to the installation. If you can't disconnect items of equipment that are sensative to test or will affect your tests you can set limitations. Ie 250volt or just test between lives and earth, then set this down as a limitation. If though I got a low reading say as your 8 on a PIR and everything was disconnected I would set the next PIR to say 3 yrs so it can tested again to see if it as deteriated more.

Same for a EIC or a MIEWC if you found the circuit you were working on was a low reading advise the client that it may pay them to have a full PIR done.

 

[T&Earth]

Hi Widdler & Malcomsanford

Thanks for replying to my post excellent advice THANKS

Steve

 

[nickblake]

As they guys have said there could be all sorts of reasons even a PIR in circuit ,or flourescent 's capacator , the easiest way to test these would be shorting out the LN and the test them between the earth if you do test the LN test at 250volts as you are less likley to blow somthing you may well have missed up , the other point is on lighting circuits all the lamps should be removed to prevent incorrect readings , and another also some of these new light fitting with little 12 volt lamps have transformers built into them