Basic installation testing with minimal disturbance

[Risteard]

He is correct to state that unnecessary dismantling has the potential to introduce faults and should be avoided. Continuity of cpcs can be proven through EFLI testing when conducting a periodic inspection and test.

That said, insulation resistance testing at 330V DC is daft. 500V DC is the correct voltage. It is, after all, a stress test.

 

[JohnW2]

That said, insulation resistance testing at 330V DC is daft. 500V DC is the correct voltage. It is, after all, a stress test.

That is obviously strictly true, but I wouldn't mind betting that it's incredibly rare to come across faults due to marginal insulation breakdown which would be apparent at 500V but undetected at 330V (or even lower).

Kind Regards, John.

 

[SimonH2]

Believe me, I have carried out many reports where landlords have had a pass previously and I have failed the installation on several (serious)counts. These have mainly been due to tampering but sometimes due to points missed in the previous inspection.

And on how many inspections have you found faults missed by the previous inspection when you have done the previous inspection ?
And how many faults would not have been picked up by IR testing at a reduced voltage rather than 500V ?

He is correct to state that unnecessary dismantling has the potential to introduce faults and should be avoided.

Thank you for confirming that. Ie, that dismantling is not a zero risk action as some would claim.

That said, insulation resistance testing at 330V DC is daft. 500V DC is the correct voltage. It is, after all, a stress test.

That is obviously strictly true, but I wouldn't mind betting that it's incredibly rare to come across faults due to marginal insulation breakdown which would be apparent at 500V but undetected at 330V (or even lower).

I am aware of one situation where exactly that can happen - and that's where "surge protector" type devices are present. Indeed, I have a couple of 4way 'surge protected' extension leads that were thrown out from work because they "failed" PAT - testing at 500V made the protection devices conduct and present a low IR.
They also have (had) a neon between live and earth, but that's a separate debate.

Other than that, it is highly unlikely that testing at 500V will show defects that won't also show at 330V (or 250V) - at least for a modern installation with modern PVC insulated cables, and nothing subjected to adverse conditions. I could see potential for older installations with (eg) cotton/rubber cables and so on.

As I see it, to comply completely with the guidelines, IR testing should be at 500V. But also to comply with the guidelines, IR testing should not be at above 330V so as to avoid unnecessary dismantling.
Given that I've tested the RCBO devices in use and shown that they don't affect an IR reading*, it comes down to which has the higher risk :
1) Introducing a fault through 'unnecessary' dismantling
2) Missing a fault that would be detected at 500V but not 330V
No-one has come up with any convincing argument for 2 being higher than 1 - accusing anyone who considers 1 to be irrational is not a convincing argument, in fact it's not an argument at all.

* As mentioned in my earlier post, they do one way round, but not the other.

 

[JohnW2]

That is obviously strictly true, but I wouldn't mind betting that it's incredibly rare to come across faults due to marginal insulation breakdown which would be apparent at 500V but undetected at 330V (or even lower).

I am aware of one situation where exactly that can happen - and that's where "surge protector" type devices are present.

Hmmm - I'm not sure that I would classify the presence of a surge protector as a 'fault'

Other than that, it is highly unlikely that testing at 500V will show defects that won't also show at 330V (or 250V) - at least for a modern installation with modern PVC insulated cables...

Exactly my point - and, I would suspect, equally true of a 50 year-old installation with 50-year old PVC insulated cables.

Kind Regards, John.

 

[Risteard]

I have come across faults which show up when insulation testing at a higher voltage which do not present themselves when insulation testing at a lower voltage so it's certainly not impossible.

 

[GaryMo]

Ignore, missed the 3 pages that followed!

 

[JohnW2]

I have come across faults which show up when insulation testing at a higher voltage which do not present themselves when insulation testing at a lower voltage so it's certainly not impossible.

I have conceded that it's not impossible (voltage-dependent insulation breakdown does occur) but, as I said, I suspect that it's extremely rare, particularly with PVC cables and modern accessories/equipment.

As a matter of interest, have you seen such cases in which the measured IR was very high with 'low' (say 250V) voltage testing, but low (low enough to fail the test) with higher voltage testing? FWIW, from very limited experience, on some of the occasions I've measured very low IRs at 500V (<1M &#937 I have, out of interest, tried with a DVM, and have got virtually the same answer at &#8804;9V.

Kind Regards, John.

 

[ban-all-sheds]

He is correct to state that unnecessary dismantling has the potential to introduce faults and should be avoided.

Yes - unnecessary. Disconnections which are necessary to carry out proper testing are not unnecessary.

But I'll tell you what is unnecessary.

It's having such an irrational concern about the risks of dismantling that you refuse to carry out dismantling which is necessary to allow proper testing to be done.

 

[JohnW2]

But I'll tell you what is unnecessary. ... It's having such an irrational concern about the risks of dismantling that you refuse to carry out dismantling which is necessary to allow proper testing to be done.

In order to know whether the concern is rational or irrational one would really need to know the probabilities, since 'rational' in this context should be based on risk-benefit considerations?

1. What is the probability of a serious incident (fire, serious personal injury) resulting from a fault which could be detected by a low IR in a <20 year-old installation which had an EICR ~18 months ago?
2. What is the probability of a serious incident (fire, serious personal injury) resulting from dismantling and then re-making a substantial number of screwed connections (including manipulation of the conductors etc.)?
3. Which of the above probabilities is the greatest?

I'm not pretending to know the answer, but that should be the basis of decided what is 'rational', not a mere assertion.

Kindest Regards, John.

 

[bernardgreen]

I am replacing the float valve in a domestic pumped sewage system. It is the type that "swims" of the surface and has three switches. At 9 volt DC there is no fault, IR looks > 200 Meg. At 50 volts DC it is about 7 Meg But at 230 volt AC the IR drops low enough to pull in the pump motor's control contactor ( the fault that caused the pump to run dry and wreck ).

So yes IR values do tend to change depending on the test voltage applied.

 

[ban-all-sheds]

I am replacing the float valve in a domestic pumped sewage system.

You get all the good jobs.

 

[SimonH2]

It's having such an irrational concern ...

I note that so far, all you can do is quote regulations (actually, recommendations, not regulations). Really, you have done nothing other than that - and you've done so in a manner which looks very much like personal abuse.

You haven't addressed any of the questions I've directed at you - I assume because you really haven't a clue about what they mean or what a valid answer may be (actually, no assumption required, for at least one of them you really have proved you don't know). Others have clearly grasped the questions and addressed them, and their significance - you clearly have not.

Further, from your responses, I've concluded a few things about you :

1) You give the appearance of having no practical experience yourself, yet you lecture others about it.
2) You make statements which anyone with any knowledge in the area can see to be false.
3) You don't appear to be as familiar with some of the documents you like to quote as you think you are.

4) And in a "pot - kettle - black" manner you call others dangerous even though you've made wrong and dangerous statements yourself.


Now I realise where you are coming from (in most cases), but bluntly, you are downright rude to a lot of people who come to this forum asking questions. I am certain that some people will be so put off by this that they will go away without having received the benefit of any education. Only a few of those will have learned enough to not do what they had planned. The net result, in my opinion, is that your over aggressive stance on slavishly following the letter of regulations is to increase danger rather than to reduce it.
I am not the only one to try and tell you this.
There's a picture that comes to mind ... http://despair.com/compromise.html

 

[bernardgreen]

I am replacing the float valve in a domestic pumped sewage system.

You get all the good jobs.

It is the house I built 30 years ago. Sold it last year and offered to "advise" on any problems that might arise. The messy bit is replacing the pump's stator which will have been worn by running dry after the float switch failed to turn off the pump.

 

[ban-all-sheds]

I note that so far, all you can do is quote regulations (actually, recommendations, not regulations). Really, you have done nothing other than that - and you've done so in a manner which looks very much like personal abuse.

If you make the choice to interpret it that way then don't complain to me that you don't like the choice you made.

You haven't addressed any of the questions I've directed at you - I assume because you really haven't a clue about what they mean or what a valid answer may be (actually, no assumption required, for at least one of them you really have proved you don't know). Others have clearly grasped the questions and addressed them, and their significance - you clearly have not.

A faulty assumption - I simply can't be rsed to discuss it with you any further, given your attitude.

Now I realise where you are coming from (in most cases), but bluntly, you are downright rude to a lot of people who come to this forum asking questions.

No - I just refuse to be a mealy-mouthed platudinous bush beater when it comes to criticising people for their actions or pointing out that they need to do some learning.

I am certain that some people will be so put off by this that they will go away without having received the benefit of any education. Only a few of those will have learned enough to not do what they had planned. The net result, in my opinion, is that your over aggressive stance on slavishly following the letter of regulations is to increase danger rather than to reduce it.
I am not the only one to try and tell you this.

And I'm not the only one to try and tell you what best practice is for inspection and testing upon change of occupancy.

I'll not be replying to any more posts from you on this topic.

 

[SimonH2]

I'll not be replying to any more posts from you on this topic.

At last, a result I asked you to STFU ages ago.