I.R. testing existing circuits

[LastManOnline]

The accepted method of I.R. testing existing circuits has been to join L and N together and test to E, to protect against damaging any electronics that were inadvertently left in circuit.
However ,with the increase of new types of circuits between L and E as a result of "intentional leakage" built in to appliances , will we need to review how we carry out I.R.testing in the near future. ?

 

[Dustydazzler]

For most part and this is just my own opinion is that and IR test should be done for initial verification ( commissioning the install )
Do we really need to IR test an install as part of any further EICRs ? Only I guess if something looks dodgy or you have some sort of intermittent fault for example.
I honestly don't feel IR tests are needed as part of any sort of basic periodic inspection

 

[DPG]

For most part and this is just my own opinion is that and IR test should be done for initial verification ( commissioning the install )
Do we really need to IR test an install as part of any further EICRs ? Only I guess if something looks dodgy or you have some sort of intermittent fault for example.
I honestly don't feel IR tests are needed as part of any sort of basic periodic inspection

But surely if the IR of a circuit is reducing at each inspection then that is a sure sign of a problem such as a cable break down. An IR test is a key test of the condition of an installation.

 

[Pretty Mouth]

The accepted method of I.R. testing existing circuits has been to join L and N together and test to E, to protect against damaging any electronics that were inadvertently left in circuit.
However ,with the increase of new types of circuits between L and E as a result of "intentional leakage" built in to appliances , will we need to review how we carry out I.R.testing in the near future. ?

Are you coming across many otherwise healthy appliances giving very low IR because of this? I can't say I've come across any myself, that I've noticed. Sometimes lowish IR, perhaps bringing the circuit down to 1 Mohms, but never low enough that I'm especially concerned by it.

 

[Lucien Nunes]

the increase of new types of circuits between L and E as a result of "intentional leakage" built in to appliances ,

Most functional leakage is due to capacitance e.g. from filter capacitors connected L-E, and from parts of a circuit that operate at much higher frequencies than 50Hz. Both of these will only occur when the equipment is connected to AC, not when subjected to a DC insulation test.

As an example, many PAT results on larger electronic appliances will show maybe 0.5-1mA of differential leakage. A 1mA resistive leakage would indicate a resistance of 230/0.001 = 0.23MΩ. Yet an IR test on the same device will usually show tens or hundreds of megohms, proving that the 1mA is capacitive in origin. The lowest actual resistance between L & E that I have seen incorporated into standard electronic goods, that would be revealed by an IR test, was 7MΩ in certain models of Sony professional video monitor.

 

[pc1966]

The lowest actual resistance between L & E that I have seen incorporated into standard electronic goods, that would be revealed by an IR test, was 7MΩ in certain models of Sony professional video monitor.

I found some RCD sockets at my parents were each around 50k L+N to E, almost certainly a deliberate thing to force-trip if N is live/open.

I initially panicked though as seeing around 0.02M (but not a dead short) when doing a quick check made me think the 50+ year old cable had gone very, very bad!

 

[LastManOnline]

Are you coming across many otherwise healthy appliances giving very low IR because of this?

No.Like you I get the expected lowish IR readings associated with all appliances.But what I am really curious about is whether any one has experienced issues where electronics may have been damaged while carring out I.R. testing between L and E ?( I have,nt )

 

[IAmSparkytus!]

Are you coming across many otherwise healthy appliances giving very low IR because of this? I can't say I've come across any myself, that I've noticed. Sometimes lowish IR, perhaps bringing the circuit down to 1 Mohms, but never low enough that I'm especially concerned by it.

Just out of interest would you not be concerned by a reading as low as 1 or even 2 megohm?

We only really carry out new install so more often than not our readings are always as high as our testers can go which is >999

Whenever I see a reading which is below 100 even I instinctively start to wonder how long before there’s a big problem!

 

[Lucien Nunes]

experienced issues where electronics may have been damaged while carring out I.R. testing between L and E ?( I have,nt )

No, and it's unlikely. It would only really occur where the test is carried out from one live conductor to earth, the other one is shorted or very leaky to earth, and the load is very small and very sensitive. Nonetheless, if one uses a method that never puts 500V across the load, one can never be accused (rightly or falsely) of damaging it as a result.

Whenever I see a reading which is below 100 even I instinctively start to wonder how long before there’s a big problem!

On ten feet of new 2.5 T+E sat on a warm dry bench, I would want to know why it only achieved such a low figure. On a typical installation in service, not so much.

 

[Dave OCD]

We did a follow up on an EICR including a CU change where a landlord 'didn't like the attitude' of the previous Electrician. It was an unsatisfactory report and the only RFC for the house had a tested IR of 0.28 Megohms across L-E which he'd given a 'FI' code to. There was also a C2 for one socket with reverse polarity - having identified this how long would it take to rectify there and then ffs ?!
We had a good look around and found a little concrete shed in the back garden with a twin RCD socket spurred off the ring, very neatly done actually. Removed this and the ring IR was over 100 Megohms on all conductors.

 

[pc1966]

Whenever I see a reading which is below 100 even I instinctively start to wonder how long before there’s a big problem!

I don't think I would worry at 100M, maybe at 10M if a small and clean looking install.

But the usual limits of 0.5/1M do seem worryingly low to me unless I could see some very reasonable explanation, maybe like a big hall of many damp and dusty lights, etc.

 

[Pretty Mouth]

No.Like you I get the expected lowish IR readings associated with all appliances.But what I am really curious about is whether any one has experienced issues where electronics may have been damaged while carring out I.R. testing between L and E ?( I have,nt )

I haven't either, however, a L-E test at 500V could be a problem if there was a N to E fault present. With N and E shorting, you would inadvertently be putting 500V across L and N. Same if there's a borrowed neutral, and the circuit borrowed from was not isolated.

Just out of interest would you not be concerned by a reading as low as 1 or even 2 megohm?

We only really carry out new install so more often than not our readings are always as high as our testers can go which is >999

Whenever I see a reading which is below 100 even I instinctively start to wonder how long before there’s a big problem!

My work's mainly minor works and fault finding on existing domestic installations, where low IR is normal, and mostly from plugged in appliances etc. Actual faults are usually right down at <0.1Mohm. I don't usually bother unplugging anything these days, unless the circuit is less than 1Mohm.

OTOH, if I was getting 1 or 2 Mohms on a circuit that I'd just installed, then yes, I'd be looking for the cause.

 

[cliffed]

IR testing is always an issue on existing installations but necessary
In large premises maybe the option would be an Earth Leakage meter on the supply to measure the IR

 

[littlespark]

I did a fault find last week.

Customer panicked as she had no socket power and a work Zoom call. In 10 minutes, I found the faulty circuit, disconnected it and got the remaining circuits live. (6 socket circuits on one rcd…. The type you need to switch to reset before it can be turned on again)

Went back Saturday morning… fault in conservatory. 20A radial. 5 double sockets.
Thought it was the one next to the dog cage, as the floor was soaking wet where they tipped their bowl. Split circuit and IR test. Clear one way, very low other way.

Tried at the other sockets and of course, the last one I opened, the one behind all the heavy furniture was the one at fault… and happened to be the first on the circuit from the board…

The cause of the fault was a rather large slug resting itself across the terminals of the socket…
The back of the socket itself was shining in slug slime.

 

[LastManOnline]

I haven't either, however, a L-E test at 500V could be a problem if there was a N to E fault present. With N and E shorting, you would inadvertently be putting 500V across L and N. Same if there's a borrowed neutral, and the circuit borrowed from was not isolated.

A point well worth emphasising this.The sequencing of I.R. tests on existing installs.Always testing N to E first.
Of course many of these faults should be picked up by rcd,s , but not all circuits are rcd protected and even when they are ,the leakage could be under the rcd threshold.
I also strongly recommend double checking that tester is on 250 volt first. 500 volt later.