EICR and IR Testing

Michael Moore:

Oh thats easy its 7.666Kohm

0.008Megohm


Which is what I alluded to on a Facebook group, and it completely baffled the bafoons there, who were apparently teachers!


 

Ah, but.. RCDs can validly trip at a residual current of anything between 50% and 100% of I_Δn so you should really be looking at keeping leakage below 15mA rather than 30mA for reliability (so perhaps 15.3kΩ rather than 7.6)


There again d.c. insulation tests only indicate simple resistance - in a real system they'll be some capacitive coupling that'll allow some extra residual current to flow too (so perhaps something significantly higher than 15.3kΩ)


Also there'll likely be leakage from appliances which likely won't be part of a fixed wiring test (even if they many appliances will have components switched off - e.g. pumps and motors of washing machines so likely to avoid the test) - so again you might want to add a significant margin on for that too..


   - Andy.

John Peckham:

Sorry Chris but fairness has never been one of my weaknesses.


IR often creeps up if the IR test button is held down especially if the installation is large as with a good IR the installation acts like a capacitor with the DC from instrument charging the capacitor. 


I would never IR test L/L on a periodic as you can never be sure everything electronic has been disconnected and I am not keen on a claim on my insurance.

When doing periodic, and doing IR Testing L-N to E Im happy with 4 meg, and will note that on the test as global test. Just dont have the time or to start stripping the install down, and then, well actually nothing as everything is mnow above 200Meg

Chris Pearson:

John Peckham:

Chris


You have fallen in to the usual trap of not understanding the major difference between Initial Verification and Periodic Inspection and Testing.

John, that's a bit unfair!


My point was that for a periodic, L-N testing is unnecessary and as the OP said, practically impossible. How would you test a socket circuit with SRCD or USB where the manufacturer's instructions are that it should be disconnected when IR testing?


As an aside, when testing at stages during erection, to start with the IR rapidly goes up to > 999 MΩ; but after a while it creeps up more slowly, especially when testing live to CPC. > 500 MΩ is certainly enough for me, but one could stop pressing the button as soon as it gets over 2 MΩ, or any value in between.

As OP, Im doing EICRs, so witjhout being rude not interested Initial Verication, which of course is where the cables are most likely to get most damage. And With BS87671 stating that 1meg is aceppatble is a complete cop out IMO. 

Sparkingchip:

I went south of the river last Thursday to do what should have been a straightforward job, until I saw the cable that supplied the central heating system that I was planning to extend.


You do have to appreciate just how bad the insulation is on some cables that are in use without tripping a RCD or MCB in a relatively new dual RCD consumer unit.

Goes to show that doing IR test dont realluy prove the safety of the install.