Insulation Resistance Testing at a Socket Outlet

[freedomrun]

Anyone give me some advice on IR Testing a domestic (tn-c-s PME) install at a socket outlet. I've been asked to replace a light fitting, so wanted to perform an IR test on the lighting circuit as part of my initial verification. The CU is packed and quite hard to access in the cupboard it's been boxed in to. If i were to leave the Main Switch off and all the MCB's closed (on) and perform my IR test at a socket outlet between L-E and N-E only, surley this will test the whole install and be adequate for a Minor Works if the readings are compliant, i would also take into account any light switches for two way or intermediate. I would prefer to test at a socket outlet as i have'nt got to perform the testing up a ladder. I know i could get some light mates testing adaptors - my question would still be the same even if i used light mates instead of connecting my IR tester to the socket outlet. Also, will this way of IR testing work on all types of boards, what if RCD's are present? Any advice appreciated - Thanks.

 

[m4tty]

How will you do r1+r2 mate without getting in the board? Or am I misunderstanding what your saying?

---------- Post Auto-Merged at 12:11 ---------- Previous post was made at 12:08 ----------

Welcome to the forum btw

 

[Doc Hudson]

Welcome to the forum, have you passed C&G 2391 inspection & testing? I suspect you would have to disconnect all accessories from every socket, turn off every fused spur and probably more to eliminate any parallel paths that would give you false readings. Should you not be advising the customer that the installation is not compliant with BS7671 as the fuse board is not accessible for inspection and testing? And it needs the boxing made removable so you can work on it. Electrical alterations from minor works are just as likely to kill anyone if there are faults, therefore require just as much due diligence as other electrical works. I do not think many competent electricians would recommend your suggested method.

Doc H.

 

[Electroglow]

Since when do u carry out a IR test from a socket point? And when testing IR from the CU the mob should be turned off ?? Am i going mad the only test carried out at a point is cont, Zs and rcd testing

But then again I hav zapped the apprentice telling him to take the earth out if the CU and pushing 500v down the ring lol , u said u can't get a shock it's turned off I think ur going mad haha but thaw just me lol

 

[davetheglitz]

If you can't access the CU I don't see you have any choice.

Since when do u carry out a IR test from a socket point? And when testing IR from the CU the mob should be turned off ?

Many older CU's are so crowded and the neutrals positions don't necessarily correspond to the MCB positions - so difficult to isolate the circuit reliably. Just turning off the MCB doesn't help much as all the neutrals are joined together.

I suspect you would have to disconnect all accessories from every socket, turn off every fused spur and probably more to eliminate any parallel paths that would give you false readings.

Why are parallel paths an issue. Surely these would make the insulation resistance worse? If the insulation resistance is within spec for the whole system it must be within spec for the individual circuit. You may not be able to measure it accurately - but you know it is compliant.

Arguably the same technique could be used with R1 + R2 by applying a short at a plug and measuring at the light (yes you'll need a ladder!) - if it's within spec then you know that it is compliant - even if your reading is not entirely accurate.

Lastly by measuring Zs at a socket and assuming the lighting Zs is Zs at the socket plus R1+R2 - if within spec you will know that the installation is within spec.

Sure - advise your customer that the board is not to spec - but if you note your method down in the notes of the MWC you've covered yourself and done the job to the best of your ability.

I do not think many competent electricians would recommend your suggested method.

Not as a default measuring technique - it's by no means accurate. However - the alternative seems to be to replace the CU and remove the boarding. I think if you insist on doing this to replace a light fitting you can guarantee not getting the job. I would go with your gut feeling - you seem to have thought things through quite nicely.

 

[Doc Hudson]

Why are parallel paths an issue. Surely these would make the insulation resistance worse? If the insulation resistance is within spec for the whole system it must be within spec for the individual circuit. You may not be able to measure it accurately - but you know it is compliant.

Yes assuming all results are good you may get away with it, but what if it is not compliant? How do you know if your circuit is ok or if it is another circuit dropping the value down? It is not uncommon for a whole board IR test to be dragged low due to the parallel effects of testing multiple circuits. I believe this concept used to be covered within the C&G syllabus. If eight circuits were all between 4Mohms, and 8Mohms the global reading would be less than 1.0Mohms. Which it would also be if seven circuits were all 20Mohms but your circuit was 1Mohms. How will you know by just doing a global test. If you have already committed to the customer that you will do the work but then find you cannot test it reliably whet do you do?

Doc H.

 

[davetheglitz]

Yes assuming all results are good you may get away with it, but what if it is not compliant?

Good point Doc - do you feel lucky! Perhaps it would be best to check before changing the fitting - then you could advise that the fault needs to be located before proceeding.

To be honest I tend to do an IR check at a socket when customers ask me to quote for a CU change as a quick and dirty check that I won't have too many problems. With lights on - assuming halogen or filament types - L and N are effectively joined so it's a reasonable measure.

 

[samson337]

I'm sorry but it must be me, I don't agree with any of the above just not the way it's done, well not in my book it's not, I all ways work in the board weather its a struggle or not that's were I join to get my R1&R2 and so on IR at the board ZS at sockets and lights RCD at sockets or some times at the board, just a bit amazed that you do it all at a socket, please don't take the above the wrong way

 

[davetheglitz]

I'm sorry but it must be me, I don't agree with any of the above just not the way it's done, well not in my book it's not

During testing I've come across a number of old Wylex boards where there is no cover over the L and N incomer - and the thought of withdrawing neutrals which may not be in any order and several crammed into a terminal to do testing in such a confined and dangerous environment sends a shiver up my spine. If you think that is the way to do things in your book you need to expand your reading!!!

As an electrician you need to think of:-

Your own safety

Your customers safety

Getting the job

Covering your backside

If none of these are compromised by adopting a slightly unorthodox testing method - why not!

 

[Sidewinder]

samson,

Yes quite, but, think about this as just food for thought.

Take a ring final circuit.

The conductors are in the form of a ring, so, you can break them at any point and get the same readings can you not.

Thus you could take, r1, r2 & rn at a socket outlet.

You can also link at an "outlet" & take R1+R2 at the board as well as the converse and get the same readings.

6 of one & half a dozen of the other as it were.

However, yes I agree work at the board where possible you are correct.

---------- Post Auto-Merged at 19:29 ---------- Previous post was made at 19:27 ----------

During testing I've come across a number of old Wylex boards where there is no cover over the L and N incomer - and the thought of withdrawing neutrals which may not be in any order and several crammed into a terminal to do testing in such a confined and dangerous environment sends a shiver up my spine. If you think that is the way to do things in your book you need to expand your reading!!!As an electrician you need to think of:-

Your own safety

Your customers safety

Getting the job

Covering your backside

If none of these are compromised by adopting a slightly unorthodox testing method - why not!

Thing is Dave if you are disconnecting & reconnecting wires in a live DB then you are breaking the STATUTE LAW.

You will get away with live testing but not this mate, you MUST isolate to remove conductors then re-energise to test then isolate to reconnect to comply with EAWR.

If you read the new green OSG there is a nice paragraph with regard to this with respect to live testing being essential, but nowt else basically!

 

[davetheglitz]

Thing is Dave if you are disconnecting & reconnecting wires in a live DB then you are breaking the STATUTE LAW.You will get away with live testing but not this mate, you MUST isolate to remove conductors then re-energise to test then isolate to reconnect to comply with EAWR.

If you read the new green OSG there is a nice paragraph with regard to this with respect to live testing being essential, but nowt else basically!

I think you misunderstand what I'm saying.

In the old Wylex boards the incomers come into the top of the isolating switch - and the screws are normally covered with plastic covers. These inevitably get lost leaving the incomer exposed on the isolating switch. These could easily be touched which is why I would not work on such a board. The hazard is present even if the isolating switch is off!!!!!

Are you saying you should pull the main fuse when working on any CU? (Light blue touchpaper ........!)

 

[Sidewinder]

Basically yes to comply with EAWR the DNO must pull the main fuse, or you must arrange for another means of isolation.

As you know it is a criminal offence for a spark to pull the DNO fuse.

 

[samson337]

Very true I'm the first for safety and allways bang on about it, I only last week was called to an old wylex board where the front cover had been badly damaged under the stairs leaving live parts accessible, so for me the right thing to do was pull the fuse, did all my test and fitted new board, needed few bits doing but all good in the end, then told the owner to get intouch with her supplier to get it resealed, I just think doing tests that way you can never get reliable results so surely from a safety point of view, it could posable that part or parts could be left in unsafe,don't see that as covering your back side

 

[Sidewinder]

samson,

With a very dangerous situation, then this is about the only legal recourse you have to pull the DNO fuse, i.e. in the immediate case of fire, or electrocution and exposed conductive parts at the origin is IMHO one of those.

 

[davetheglitz]

As you know it is a criminal offence for a spark to pull the DNO fuse

It most certainly is - and I'm sure there must be someone who has been prosecuted for this - somewhere - sometime.

Surely the point about most CUs is that the isolator is built in to remove power to the system. The fact that it's within the same enclosure isn't generally an issue.

How can anyone do a PIR at a reasonable price if you have to build in calling the DNO, ensuring someone is at home to receive them, attending to do the job, and getting DNO to reconnect?

 

[samson337]

Hi sidewinder, I agree it can be done like that, but sorry my point was I just think it's better to do it at the board, more organised for me to do it that way, that's why before a board change I all wats do periodic and test all circuits one by one that way I'm sure I won't have a problem at the end

 

[Sidewinder]

Dave,

This is one of the fundamental errors with the system especially since the fragmentation of the market & the formation of the DNO's.

Problem is there is never a requirement to pull the main fuse, by the DNO it is never required, because the have no evidence of the requests of such an act, so why should they provide a suitable service.

It is because almost all sparks, and this includes the LA housing people pull the fuses themselves.

This is "muddied" by the fact that some DNO's & some electricity providers have their own contracting arms in direct competition with the independent contractor, and their guys are "authorised" to pull fuses, this it is not a level playing field.

To me it smacks of corruption to be honest and a planned attempt to put the independent contractor out of business.

 

[davetheglitz]

Hi SW,

I wondered where this was going until you came up with this little gem!

Wholeheartedly agree with you - but as an independent contractor who is quite frankly struggling I don't see where my options are!

I will continue to work on decent CUs with satisfactory isolators - and pray to the Seal Fairies that things will improve!

 

[samson337]

And it's True, I no a good few sparks who do pull the main fuse including my self no pun intended, how would you ever get the job done on a board change or dangerous situation if you don't pull the main fuse if no isolator, can I ask is this what you wanted to hear all along

 

[davetheglitz]

With a very dangerous situation, then this is about the only legal recourse you have to pull the DNO fuse, i.e. in the immediate case of fire, or electrocution and exposed conductive parts at the origin is IMHO one of those.

Is it fair to say it's dangerous because some thoughtless person had removed the cover of the CU before I got there?

Perhaps the Seal Fairies have answered my prayers!