"17th Edition CUs" & "Amd3 CUs"

[davelx]

Not really - 531 is about "Devices for fault protection by automatic disconnection of supply" and, indeed, the whole of Chapter 53 is about "Protection, Isolation, Switching, Control and Monitoring". It is Chapter 41 that is about protection from electric shock.

As I said, particularly in the case of TT installations, RCDs can be required for reasons (e.g. fire prevention) other than (in addition to) protection against electric shock - so I think it could be argued that 531.3.1.201 does not apply in such circumstances.

The distribution circuits in my (TT) installation are provided with fault protection by RCDs. I wouldn't say that protection against electric shock was the 'primary' (certainly not the only) reason for this, and I therefore suspect that a SP RCD/RCBO would, strictly speaking, not conform with a combination of 531.1 and 531.3.1.201.

Kind Regards, John

In the draft version linked to earlier, the title of 531 is

"Devices for protecton against electric shock by automatic disconnection of supply"

Has that changed in a later version?

 

[EFLImpudence]

That seems like a firm claim that you have no idea how common MCB trips for unknown reasons are compared to RCD trips, and yet it is only the situation where what would have been an MCB trip for unknown reasons becomes an RCBO trip for non RCD reasons where any disadvantage arises.

Ah, so there are disadvantages.
I didn't say I did know how common this or that is. You are arguing with what I wrote so I assumed you knew how common things were.

In short, you have no idea how likely it is that this disadvantage which exercises you is purely theoretical, never actually arising in practice.

I said it was A disadvantage.
You seem to agree judging by the above sentences.

Firstly, why do you discount L-E and N-E short circuits?

Did I say I did discount them? I don't think you are concentrating.

Secondly, that's more a case of what you don't do (i.e. think about possible causes), so I'll rephrase my question:

No, it is what I am able to do in the circumstances - discount them.
Surely not having to do things is an advantage.

What positive testing/inspecting/other-physical actions do you initially do which is different to what you would do when initially investigating an RCBO trip?

Why does there have to be a positive testing/inspecting/other-physical actions scenario?
Not having to test several things, which would otherwise be necessary, is a positive advantage in itself.

I have no information on how likely it would be that there would be an overcurrent cause not flagged by phenomena such as flashes/bangs/smells of burning or the powering on of a specific item to judge whether it would create a real practical disadvantage worth considering.

So - it might be the case.

And neither do you - all we do know is that might be a "so what, that is of no consequence in practice".

...but I think it is - as it is clearly evident in practice - and you seem to have no evidence to the contrary.

 

[JohnW2]

In the draft version linked to earlier, the title of 531 is ... "Devices for protecton against electric shock by automatic disconnection of supply" .... Has that changed in a later version?

Ah, sorry, you're right. That change appeared in the DPC - I was looking at 17th (Amd3).

That does seem to make it sillier, and may well represent a mistake made by the authors, but I'm not sure that the title of 531 necessarily alters the implications of what the regulations actually say. The only other difference between 531 (which says that all live conductors must be disconnected) and 531.3.1.201 (which says that neutral does not have to be disconnected) is that the latter is qualified by 'For protection against electric shock ... " (the implication presumably being {despite the title of 531} that the reg does not apply if the RCD is being used for something other than protection against electric shock.

There is also the matter of 531.2.2.201 - which says, for OPDs, exactly the same as 531.3.1.201 said about RCDs in the DPC (before removal of the initial clause).

The main problem, as I see it, is that we cannot be certain of which of the two contradictory meanings is intended.

Kind Regards, John

 

[ban-all-sheds]

Ah, so there are disadvantages.

But maybe only theoretical ones. Maybe ones so rarely encountered in practice that they are not worth remarking on, or considering to be disadvantages in any meaningful sense.

I didn't say I did know how common this or that is. You are arguing with what I wrote so I assumed you knew how common things were.

I've been asking you what the disadvantages actually are. If I'm arguing with anything it is the unqualified acceptance that a theoretical problem is a disadvantage with no regard to how common it would be to encounter the problem.

I said it was A disadvantage.
You seem to agree judging by the above sentences.

I don't think you are concentrating - read what I wrote, again.

it is only the situation where what would have been an MCB trip for unknown reasons becomes an RCBO trip for non RCD reasons where any disadvantage arises.

In other words, this disadvantage only arises when the condition would have tripped an MCB for unknown reasons.

If that's an almost unheard of condition, then the disadvantage is equally unheard of.

If in the context of the successful or effective operation of a consumer unit there is an unfavourable circumstance of such vanishingly small probability that it is more likely than not that someone would never encounter it then it is not a disadvantage worth considering or mentioning.

Did I say I did discount them?

Yes:

Discount overload and short-circuit causes.

No, it is what I am able to do in the circumstances - discount them.
Surely not having to do things is an advantage.

Whether it is or not depends on whether you would have had to do them.

A unicorn-proof enclosure is only an advantage if without it you would have to investigate for unicorn damage.

Why does there have to be a positive testing/inspecting/other-physical actions scenario?
Not having to test several things, which would otherwise be necessary, is a positive advantage in itself.

There is no advantage to be had in not doing things you would not have had to do in the first place.

My basic question to you, all along, has been WHY is it a disadvantage to not be able to tell from looking at the device if a trip was caused by overload or fault.

So yes, the positive testing/inspecting/other-physical actions scenario is important. You can't tell why the device tripped, but if that makes no difference to the work that you have to do to find the cause of the trip then how can the not being able to tell reduce the chances of the success or effectiveness of that work?

So - it might be the case.

It might be.

It might be the case that in a population of 100,000,000 consumer units there would be one instance every 50 years of an overcurrent cause not flagged by phenomena such as flashes/bangs/smells of burning or the powering on of a specific item.

If that were the case then by how much would that instance reduce the chances of success or effectiveness of the device helping someone find the cause of the trip?

...but I think it is - as it is clearly evident in practice - and you seem to have no evidence to the contrary.

If it is clearly evident in practice then you must have clear evidence of how often, in practice it is of consequence. That's what "clearly evident in practice" means.

The only evidence either of us could have is data on how often not being able to tell from the device why it tripped is of consequence. It's not a question of "evidence to the contrary", it's simple statistical data. How often does it happen? If you add up all of the hours an electrician spends over his career trying to find why a device has tripped, to what extent does not being able to tell why an RCBO has tripped reduce the chances of the success or effectiveness of those efforts?

 

[EFLImpudence]

But maybe only theoretical ones. Maybe ones so rarely encountered in practice that they are not worth remarking on, or considering to be disadvantages in any meaningful sense.

Sod's law, then.

I've been asking you what the disadvantages actually are. If I'm arguing with anything it is the unqualified acceptance that a theoretical problem is a disadvantage with no regard to how common it would be to encounter the problem.

So should I have said theoretical disadvantage?

it is only the situation where what would have been an MCB trip for unknown reasons becomes an RCBO trip for non RCD reasons where any disadvantage arises.

That must have been what I was talking about.

In other words, this disadvantage only arises when the condition would have tripped an MCB for unknown reasons.

Q.E.D.

If that's an almost unheard of condition, then the disadvantage is equally unheard of.

...but is it unheard of? Where did I hear of it (or think of it myself)?

If in the context of the successful or effective operation of a consumer unit there is an unfavourable circumstance of such vanishingly small probability that it is more likely than not that someone would never encounter it then it is not a disadvantage worth considering or mentioning.

It is not unheard of. If an RCCB trips you know it was not overload nor short-circuit - see definitions.

Yes:

No. See definitions.

Whether it is or not depends on whether you would have had to do them.

So - If I had to do them, then...

A unicorn-proof enclosure is only an advantage if without it you would have to investigate for unicorn damage.

I think what I am saying is considerably more prevalent than unicorns.

There is no advantage to be had in not doing things you would not have had to do in the first place.

Except when you would have to do them because of the situation I mention.

My basic question to you, all along, has been WHY is it a disadvantage to not be able to tell from looking at the device if a trip was caused by overload or fault.

Because if you know that trip was not caused by overload nor short-circuit then it saves time and effort.

So yes, the positive testing/inspecting/other-physical actions scenario is important. You can't tell why the device tripped, but if that makes no difference to the work that you have to do to find the cause of the trip then how can the not being able to tell reduce the chances of the success or effectiveness of that work?

Not the effectiveness of the work but the time and effort doing that work when a number of causes can be discounted.

It might be.

Q.E.D.

It might be the case that in a population of 100,000,000 consumer units there would be one instance every 50 years of an overcurrent cause not flagged by phenomena such as flashes/bangs/smells of burning or the powering on of a specific item.

It might not be that rare.
Why then do we get so many people asking why their MCBs have tripped?

If that were the case then by how much would that instance reduce the chances of success or effectiveness of the device helping someone find the cause of the trip?

It could save time and effort.

If it is clearly evident in practice then you must have clear evidence of how often, in practice it is of consequence. That's what "clearly evident in practice" means.

If it is possible to happen then it will happen.

The only evidence either of us could have is data on how often not being able to tell from the device why it tripped is of consequence. It's not a question of "evidence to the contrary", it's simple statistical data. How often does it happen? If you add up all of the hours an electrician spends over his career trying to find why a device has tripped, to what extent does not being able to tell why an RCBO has tripped reduce the chances of the success or effectiveness of those efforts?

I don't know how often it happens but that does not mean when it does it is not advantageous.

 

[ban-all-sheds]

Sod's law, then.

Logical, reasoned thinking, sound engineering practices and evidence-based policies would be better.

So should I have said theoretical disadvantage?

It might have helped you to focus on whether it was a concern worth consideration.

That must have been what I was talking about.

Indeed.

But over and over again you have refused to say whether that situation is common enough for it to be a disadvantage of any consequence.

...but is it unheard of?

I don't know, because over and over again you have refused to say whether it is or not.

Where did I hear of it (or think of it myself)?

I don't know, because over and over again you have refused to say whether you have heard of it, or whether you have only imagined its existence.

It is not unheard of. If an RCCB trips you know it was not overload nor short-circuit - see definitions.

Please don't insult everybody's intelligence by thinking that you can get away with that.

The "unheard of" event is a fault which trips an MCB and is neither accompanied by any observed signs such as noise/flashes/smoke nor obviously associated with the operation of an accessory or load.

Because that is the only scenario where you're worse off with an RCBO.


Earth faults tripping an RCCB - could be all sorts of causes.
Earth faults tripping an RCBO - could be all sorts of causes.

So no worse off there. Better off, in fact, as there's less to search than with an RCCB covering several circuits.

Overcurrent tripping an MCB, accompanied by a bang/flash/smoke from an appliance or switch, or clearly associated with turning an appliance on - pretty good clues there as to where to look for the cause.
Overcurrent tripping an RCBO, accompanied by a bang/flash/smoke from an appliance or switch, or clearly associated with turning an appliance on - pretty good clues there as to where to look for the cause.

So no worse off there.

Overcurrent tripping an MCB, with no bang/flash/smoke from an appliance or switch, and not clearly associated with turning an appliance on - no clues there as to where to look for the cause.
Overcurrent tripping an RCBO, with no bang/flash/smoke from an appliance or switch, and not clearly associated with turning an appliance on - no clues there as to where to look for the cause, plus no idea whether the cause is overcurrent or earth fault current.

But over and over again you've refused to say how common that scenario is.

So - If I had to do them, then...

Then...

What would they be?

All you know is that an RCBO has tripped, and that there's no evidence of a bang/flash/smoke from an appliance or switch, and that it didn't happen in circumstances which could be associated with turning on an appliance.

What's different, at that point, about what you do to find the cause than what you would do were it an RCCB which had tripped?

What's different, at that point, about what you do to find the cause than what you would do were it an MCB which had tripped?

I think what I am saying is considerably more prevalent than unicorns.

Over and over again you have refused to present any evidence that that is the case.

Except when you would have to do them because of the situation I mention.

So what are those things?

Because if you know that trip was not caused by overload nor short-circuit then it saves time and effort.

What investigations do you not have to bother with?

Not the effectiveness of the work but the time and effort doing that work when a number of causes can be discounted.

Time and effort counts towards effectiveness.

You start out knowing that a device did not trip because of overcurrent. How does that help you find where and what did cause the trip faster?

Q.E.D.

No.

It might not be that rare.

It might not be. But over and over again you have refused to say how rare it is

Why then do we get so many people asking why their MCBs have tripped?

How many do we get asking that when there is no indication of the trip being associated with any other know event?

It could save time and effort.

How much, and how often?

If it is possible to happen then it will happen.

But not necessarily often enough for it to be of any concern.

I don't know how often it happens but that does not mean when it does it is not advantageous.

Nor does it mean that when it does it is not inconsequential.

 

[EFLImpudence]

Ok.