Mixed brand MCBs and EICR coding

[stillp]

But a CU is not just a 'box'!

 

[stillp]

So, you, who would no doubt claim to be a rational person, would prefer to use devices in a way contrary to good engineering practice and their manufacturers' instructions, than to use devices in the way recommended by the manufacturer but about which you have been warned that misusing them might lead to a change in their operating characteristics?

That's not quite what I said. I frankly find it very hard to believe what you have told me, but if it really is true that the design and/or manufacture of some of these products is so poor/marginal that they are "quite likely" to fail to perform satisfactorily if installed in a different box, then I would be extremely concerned about that. I would regard that as a very rational concern and much greater than my current concern about this other theoretical 'potential danger', for which no-one so far seems able to to provide me with any evidence.

Kind Regards, John

Ah, I see. Your theoretical danger is bigger than my theoretical danger!
Don't be so surprised. When testing a product (any product), it has only to meet the test requirements, not to exceed them by any particular margin, although the test requirements can exceed the normal service requirements. Any change in operating conditions might therefore result in a change of performance.

 

[stillp]

re you seriously suggesting that, in the absence of faults, the temperature of a device could possibly differ by as much as 60° from the temperature of another device of the same rating, carrying the same current and compliant with the same relevant Standard(s), but from a different manufacturer??

No, I didn't suggest that at all. You stated that you would be surprised if a 20°C temperature rise would cause a problem. I asked you if you thought a 60K rise would cause a problem. You haven't answered that question.

 

[SimonH2]

A good professional panel builder will design and verify the panel to an appropriate standard, such as 61439. The verification might well include type-testing. I don't know any that would mix makes of MCB in a single panel, but most would be happy with a different supplier for enclosures and protective devices.

So when assembling a panel, they won't (for example) fit (say) a Finder relay alongside (say) an MG breaker ? And won't (say) put a Siemens PLC on the other side of the breaker ? And they'll "verify" correct tripping characteristics of each breaker under all different combinations of states of the neighbouring devices ?
And then type test a one off panel ?
Pull the other one, it's got bells on.

I take some medicines that are accompanied by certain safety warnings. I might not understand the science behind those warnings, but I don't expect the manufacturer to show me evidence to support them. I just accept that they probably know more about their products than I do, and obey the warnings.

On the other hand, I think a better suggestion is that we have regulators who are in a position to check the evidence on our behalf - and sometimes they do have to ban medications that the manufacturer has told us are safe. So when I take medication, I work on the basis that the regulator probably isn't asleep on the job.

But a CU is not just a 'box'!

Remove the breakers and main switch - and there's not much else but the box.

 

[stillp]

So when assembling a panel, they won't (for example) fit (say) a Finder relay alongside (say) an MG breaker ? And won't (say) put a Siemens PLC on the other side of the breaker ? And they'll "verify" correct tripping characteristics of each breaker under all different combinations of states of the neighbouring devices ?
And then type test a one off panel ?
Pull the other one, it's got bells on.

They will (should) design the panel so that it functions correctly. If they had a row of 10 MCBs, they'd almost certainly be from the same manufacturer, if only to get a better quantity discount.
Yes, the better panel builders will verify the performance of a one-off to the same degree of rigour as when type-testing a production design.

On the other hand, I think a better suggestion is that we have regulators who are in a position to check the evidence on our behalf - and sometimes they do have to ban medications that the manufacturer has told us are safe. So when I take medication, I work on the basis that the regulator probably isn't asleep on the job.

I don't really understand what you're saying there. The regulator won't have tested various combinations of drugs. I'm not aware of any drugs that have been banned unless a concern has been raised and has come to the attention of the regulator. Maybe someone else is aware?

Remove the breakers and main switch - and there's not much else but the box.

Then it isn't a CU any more. Anyway, what about the busbars?

 

[JohnW2]

However, you are missing much of the point of ALARP. (strangely enough I was discussing this with a senior HSE official only last week). It starts from the premise that any risk that can be reduced, should be the subject of remedial action.

I can't argue with whatever your official said, but that differs from what has been said at the HSE seminars I have attended. As I said (by way of a quote from HSE documentation) my understanding is that a basic principle of ALARP is that it involves - "weighing a risk against the trouble, time and money needed to control it." - and one cannot undertake such a 'weighing' if one has no clue about the magnitude of the risk.

I don't care whether the evidence/facts comes from manufacturers, academia, independent organisations, government bdioes or wherever, but if you want me to believe it, you have to show me some evidence.

We all do that all the time. I take some medicines that are accompanied by certain safety warnings. I might not understand the science behind those warnings, but I don't expect the manufacturer to show me evidence to support them. I just accept that they probably know more about their products than I do, and obey the warnings.

Sure, none of us has expertise in every field, so we have to delegate the examination of evidence to some trusted and reputable overseer or regulatory authority. The safety warnings to which you are not the view of the manufacturer but, rather, are created and/or approved by a regulatory authority who have undertaken very rigorous scrutiny of vast amounts of data and 'evidence', and I have enough faith in the competence of such authorities to accept that their recommendations, warnings etc. are based on very solid evidence, even if I have personally not seen and/or understood the evidence.

In context, if some comparable national or international authority had examined a lot of data and evidence, and on the basis of that examination had expressed their view that it was unsafe to have mixed-make protective devices in a CU, then I would accept that view, even if the actual evidence were not available to me.

Having said that, in the case you mention of a medicine, at least a summary of that data/evidence, and the authority's reasoning in reaching their conclusions, would be available to me, since that is placed in the public domain.

Kind Regards, John

 

[Iggifer]

Remove the breakers and main switch - and there's not much else but the box.

Then it isn't a CU any more. Anyway, what about the busbars?

And the neutral bars, earth bars and neutral tails

 

[JohnW2]

Ah, I see. Your theoretical danger is bigger than my theoretical danger!

It's not "my theoretical danger". Even though I continue to find it hard to believe, you were the one who asserted that it was "quite likely" that a protective device would fail to perform satisfactorily if housed in the wrong enclosure. Am I the only person who would regard that as a frightening product, which I certainly would not want to be protecting me or my electrical installation??

Kind Regards, John

 

[stillp]

a basic principle of ALARP is that it involves - "weighing a risk against the trouble, time and money needed to control it." - and one cannot undertake such a 'weighing' if one has no clue about the magnitude of the risk

I disagree, of course one can, if the time, trouble and money needed to control a risk is zero, then the magnitude of that risk does not matter.
[/QUOTE]

Sure, none of us has expertise in every field, so we have to delegate the examination of evidence to some trusted and reputable overseer or regulatory authority. The safety warnings to which you are not the view of the manufacturer but, rather, are created and/or approved by a regulatory authority who have undertaken very rigorous scrutiny of vast amounts of data and 'evidence', and I have enough faith in the competence of such authorities to accept that their recommendations, warnings etc. are based on very solid evidence, even if I have personally not seen and/or understood the evidence.

In context, if some comparable national or international authority had examined a lot of data and evidence, and on the basis of that examination had expressed their view that it was unsafe to have mixed-make protective devices in a CU, then I would accept that view, even if the actual evidence were not available to me.

Fair enough. I have more confidence in (some) manufacturers than I do in most so-called 'independent' test houses, but that's just my personal experience. However, I must point out that the absence of any warning against using mixed-make protective devices in a CU does not constitute evidence that it is safe to do so. While typing that I had a nagging thought that there was something published some years ago - perhaps by the ESC. Must ask Mr Google when time permits.

Having said that, in the case you mention of a medicine, at least a summary of that data/evidence, and the authority's reasoning in reaching their conclusions, would be available to me, since that is placed in the public domain.

That's interesting, thanks. Where might that data be found?

 

[SimonH2]

... what about the busbars?

And the neutral bars, earth bars and neutral tails

All of which can also be removed, replaced, changed around without notification. But they are also not active components and I challenge someone to come up with a plausible explanation of how any of them might influence the operation of an MCB.

And no, I don't consider the magnetic field from the currents in them to be a plausible disturbance.

 

[stillp]

I don't consider the magnetic field from the currents in them to be a plausible disturbance.

Even while interrupting a 6kA fault?

I was thinking more of poor connections to the busbar, particularly on clip-on designs.

 

[kai]

This is an interesting loophole, If I had a Wylex plastic board, and replaced it with a Wylex metal board, but transplanting the entire din rail and contents, intact from the old board, into the new board, that won't strictly count as a CU change, because the original breakers, busbar, RCD and mainswitch are all the original ones, in the same order as the old unit, just sitting in a new Wylex metal box - what do you think??

 

[Iggifer]

This is an interesting loophole, If I had a Wylex plastic board, and replaced it with a Wylex metal board, but transplanting the entire din rail and contents, intact from the old board, into the new board, that won't strictly count as a CU change, because the original breakers, busbar, RCD and mainswitch are all the original ones, in the same order as the old unit, just sitting in a new Wylex metal box - what do you think??

I think you'd be on VERY thin ice come the sale of a house etc with no compliance certificate for that. Not sure 'it's the same breakers as were in the plastic one' is gonna wash, particularly when it's still the current range of breakers

 

[EFLImpudence]

This is an interesting loophole, If I had a Wylex plastic board, and replaced it with a Wylex metal board, but transplanting the entire din rail and contents, intact from the old board, into the new board, that won't strictly count as a CU change, because the original breakers, busbar, RCD and mainswitch are all the original ones, in the same order as the old unit, just sitting in a new Wylex metal box - what do you think??

The words are "replacement of a CU"'

If you take one off and fit another you are replacing it.

 

[SimonH2]

Even while interrupting a 6kA fault?

Well true - but then the various wiring which may follow any arbitrary routes would also offer a similar perturbation. Given that the magnetic circuit inside a breaker has small air gaps and iron paths (I have teken them apart in the past out of curiosity), I reckon it would need a very significant magnetic field to affect it - unless it's a crap design.
As John says, if something was that bad I wouldn't want it protecting my house !

I was thinking more of poor connections to the busbar, particularly on clip-on designs.

I have to admit I hadn't thought of anything but the screw terminal types.