EICR IR testing for newbies

[kayloh]

I'm qualified now to test and inspect with my company, which I've worked with for years and they are now about to send me out alone. Scary days ahead

I've only ever had one issue with doing EICR's at training and its to do with IR testing. Here's a few questions for any of the experienced testers that would be helpful for me and anyone else that is in a similar situation.

Case scenario: In a residential home it would be ideal to disconnect everything plugged into the sockets, lamps, neons etc. before doing an IR test. However if these are council homes we are not getting paid enough to disconnect all these appliances due to time constraint and money. If you interlink L-N and test between the link and earth does it bypass EVERYTHING on the circuit and give a trustworthy reading?

Case scenario 2: I've heard discussions from my office between the inspectors that check the OP's certs and the OP that filled in the cert, and its to do about low IR's on a RCD protected MCB. The inspectors in the office believe that an IR of 0.8Mohms from a cert is too low and should be tripping the RCD, which I don't entirely agree on. How low does the IR have to be before it starts tripping the RCD? I've read that using ohms law you can derive 230V/30mA=7666 ohms which is the reading that should trip a 30mA RCD, is this true or are there factors that could raise this?

Any other tips like what to look out for would be helpful please, Many thanks for taking your time to read this.

 

[ferg]

It doesn't bypass everything it prevents damage to said loads by not shoving 500v into it's delicate bits.

You can end up with skewed readings as each connected loads IR is measured in parallel so the reading will be lower than the lowest IR of the connected loads not the lowest IR of the fixed wiring.

The second bit is basic maths. ^^

 

[westward10]

There is no need to unplug everything or remove lamps, neons etc...
Do your IR test with the neutral disconnected and with it connected to the line conductor, L/N reading can be omitted but on some socket circuits it can be achieved. If you get low readings say below 1.0 meg when testing at 500v then retry at 250v as filtered equipment can throw voltage to earth at 500v. Rcd sockets and spurs will need the cpc/s disconnecting at the accessory. Other low readings may require some unplugging before you decide there maybe a fault present.

 

[westward10]

Must admit I never link the L/N together.

 

[kayloh]

I must admit, I would hate to cry wolf too many times because of low IR's with the fault finders saying that it was due to a hidden appliance. I feel like the inspectors might not fully trust me at first but I guess that's the learning experience I must endure.