IR Testing Domestic install by Back testing at a socket outlet

[freedomrun]

Can anyone give me some advice on Insulation Resistance Testing a domestic install by means of 'Back Testing' at a socket outlet. I'm writing this with regard to MW and PIR - As a retired Sparky told me recently that if i test between L&E then N&E with all Fuses in or Mcb's on in the CU (disconnect any rcbo's or rcd's in the install) and turn OFF the main switch, then this will test the entire install in one hit & as long as the readings are above that stated in BS7671, then all ok. Does this method get used much? I can see the advantages as no need to remove lamps and appliances with plug tops, just need to check switches for strapers and test again. I would'nt do an IR test between L&N with this method of course, just record it as a LIM on the results (due to not knowing what the customer may have connected & maybe no access). I understand this way of testing would be no good on a new install when doing an EIC, just looking at using this for MW & PIR and also for previewing any work before quoting an install to give an idea of what the IR may be like. I've not used this method before, anything i should keep in mind before i try it out that i might have overlooked. Many Thanks in advance.

 

[johnboy6083]

i cant see any reason why this wouldnt work, but surely, one of the places you would want a decent look at during a PIR/EICR is the CU/Fusebox. for that reason i would do it then. Also i wouldnt just do the L-E and N-E, unless i couldnt disconnect everything. the tip to checking for connected loads is to test at as close to operating voltage first. ie, if your testing 1ph, then test at 250 before upping to 400. you will notice that any connected loads will give low readings

 

[truckster]

It's easier to do at the CU, you will have it open anyway so just link the neutral bar to the top of an MCB and test to earth. Make sure you turn off the board and remove the link after testing!

 

[Blowcat]

I have only heard of this from 1 other person. For 99.9% of the time it will never work. I can't remember the last time I could turn off a whole install and do continuity and IR test.
Better off doing it at the DB.