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]

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.


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.

Reminds me of my college days when ever we did IR tests on our test circuits we always got 999MO because everything was wired in such short cable. The teacher kept having to remind us in the 'Real World' we should not expect such a high IR reaching.

Out of curiosity what would the average Sparks deem an unacceptable IR reading for an in service install , 2MO 3MO would you want to investigate further ?

 

[LastManOnline]

Out of curiosity what would the average Sparks deem an unacceptable IR reading for an in service install , 2MO 3MO would you want to investigate further ?

While acceptable from the regs point of view ,in practice you would be unhappy, possibly concerned with such readings.There is certainly trouble on the way.

 

[littlespark]

Reminds me of my college days when ever we did IR tests on our test circuits we always got 999MO

My college days we did IR tests on other apprentices!

 

[Dustydazzler]

My college days we did IR tests on other apprentices!

Not at college but one of my first weeks on-site doing a big PIR on an old house the lead sparks got me to drop a socket off and told me to hold onto the bare cpcs and he went off and did an IR test at the board. I should have known better but when you are green you do what you are told. I wonder what reading he got with me in the circuit

 

[westward10]

If you hold the ends and press the button once the initial jolt happens you can't really feel it even on 1kv.

 

[littlespark]

We used an old wind up tester at college… it was a test to see who could hold the lead pins the longest as it was wound faster and faster.

Fingertips went numb, and the pins just slipped out.

 

[LastManOnline]

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

I,m slightly off topic here ,but I felt I should say that I,m largely in agreement with what you say.Certainly ,I cant see the point of extensive electrical testing of a 5 year old family home ,when in reality a thorough visual inspection should suffice (plus testing of all safety devices).
Now a 50 year old home ?Thats a very different matter.
But whether 5 or 50 ,I regard extensive visual checks as my number one source of information in determining the health of an electrical installation.Standard electrical testing then supplements it.
Did a periodic on Wednesday on a recently renovated older house which is up for sale.Looked great and I felt optimist.All the standard testing gave excellent results.
When I began removing accessories though I discovered undersized wiring at many sockets.Secondly the new wiring visible at the DB often extended only to the first point on the circuit where it was joined to the original wiring.It all looked professionally done too.It set off alarm bells immediately.
I dont believe it possible to experience "a breakdown of insulation" in a modern home,certainly not through deterioration.And as Dusty alludes to the insulation is only really compromised (in my experience to) when some unconventional activity has occured in the home ,be it intentional or unintentional and this will almost always manifest itself either visually ,audibly ,via odour or through operation of one of the safety devices.

 

[Simon47]

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.

The RCBOs we have in our rental properties have about 65k to earth one polarity, >999M the other - so can only do in-circuit tests at one DC polarity. But overall there's a fair bit of capacitance in the installation such that my MFT can't get a decent reading. So I break out dad's old "press and hold - wait till the needle stabilises" meter, and with that I can do the whole installation at once which saves a lot of work dropping tails out of the breakers (and the associated risks of not getting them back in properly).

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've never seen anything, and up to 350V DC (peak voltage of 250V sine wave) it's hard to see how something survived on mains power anyway. Between 350V and 500V really isn't that much, so I'd have thought anything so marginal would get knocked out by the occasional surge anyway. So personally I'd not have any concerns testing at 500V unless I knew there was something both sensitive and expensive.

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

I know what you mean - it just "feels wrong" even though we know it's OK according to the regs. Even down to 1M, that's only 0.25mA and a grand total of ... drumroll ... 62mW of power being dissipated along "a fair bit" of cable. But as you say, for something that at one time would have been too high for our meters to measure, why is is so much worse now ?