It has indeed - but this thread is specifically about RCDs (the clue is in the title). Furthermore, if it were still about C2 RCBOs, it wouldn't be a 'spin-off' topic!
He's certainly the one who posted lots of information about Standards for RCBOs and I (probably also still thinking of that other thread!) innocently responded to it at length!
That's true - but, in context, I think it was pretty clear that we were not talking about RCBOs, wasn't it? Per the title, it's a generic discussion about whether or not reliance on RCDs for ADS in TN systems is compliant with regs, and most CUs don't have RCBOs, and certainly don't have banks of MCBs run off RCBOs!
Yes, I know - if you recall I dissected a Protek one recently, and that certainly didn't have a functional earth wire. However, you're confusing me by saying 'as well' - until mfarrow introduced the RCBO Standards, we were discussing whether electronic RCDs (RCCBs) could fail to work if L-N pd fell too low. A functional earth, even if there were one, would not make any difference to that.
When you say 'normal', do you mean 'non-electronic'? If so, I'm no longer certain that they still exist - I asked in the recent thread if anyone had taken recent ones of reputable makes apart, but got not answers. What you say about compliance corersponds with the view I've expressed, but some people seem to disagree. In any event, the regs certainly don't distinguish between electronic and non-electronic RCDs, so whatever one believes the regs are saying, it would have to apply to both.
Typo now corrected
The RCD descriptions are identical in both standards BS EN 61008-1 and BS EN 61009-1, so the only things which are dependant on voltage are the RCD elements. I can't imagine why the MCB elements would be dependant on voltage being present.
It just has "Service Continuity" with Yes or No in the table, with a footnote of "This information is given for guidance only" and nothing in the definitions.
That marking is, I quote:
Yes, in the definitions of both standards:
Yes, in the definitions of both standards:
I certainly didn't accuse you of attempting to 'deceive', and nor do I think anyone else did. I thought you'd probably made a mistake, aided by the fact that (as BAS said), this thread is a spin-off from one about RCBOs. ... The standards may be similar but, at least in the past, there has seemingly been a significant difference between the devices. Maybe it's down to lack of exposure/experience, but I've never seen or heard of an RCBO in which the residual currenmt part was not electronic, whereas, at least in the past (I'm not so sure any more) at least some RCDs did not use any electronics.
I'm not sure I understand that, or its relevance.
Thanks.
Nor can I, and I wasn't suggesting that it would.
Quite. The statement is so confused/confusing that I think we simply have to ignore it for the time being! As you say, what on earth could be meant by "earth fault arising due to [or on] failure of line voltage"?!! My question therefore must essentially remain unanswered.
The more one hears about this document, the worse it gets!
I wasn't asking for more details of the marking
I was noting that there is far less functional information about this class of device than about the other three, and therefore wondered if anymore (functional) details were available.That seems essentially to be 'defining' the phrase by paraphrasing it
I suppose your answer is bound to be 'yes', but what I was asking is whether 'not dependent on line voltage' really does mean that it still works if line voltage falls to zero. If so, I still don't understand how it can work if the device has and electronic+solenoid mechanism of operation.
Thanks. Yes, I've seen inside many an RCD like that in my time, but I probably haven't seen inside one that was manufactured in the last several years - hence my uncertainties as to whether non-electronic ones have been manufactured in recent times. The ones in the videos look fairly 'young', but one can't be sure. I didn't notice a manufacturing date in any of the pictures, did you? Conversely, as you know, I recently saw inside a Protek one which had been in service for around 9 years, which was electronically operated.
Indeed, I've already made that observation. However, even if the power to the electronics is maintained for a while by a capacitor for long enough for the SCR to be triggered, it still won't work in the absence of at least some AC supply, since there will be nothing to power the solenoid.
True, but it's not actually 'loss' of supply, in that sense, that this (and similar) discussions is about - it's about reduction to near zero of the L-N pd across the RCD terminals due to and L-E or L-CPC fault within the installation. As I've observed, I think this is only a possibility with a fault extremely close to to the RCD with a TN-C-S supply.
Again, we're not really talking about that sort of 'loss'. You're obviously right about that theoretical hazard, but the chances of a leak to earth occurring in the installation at the same time as there is a total loss of neutral must be incredibly small. Anything short of total loss would probably leave enough power for the RCD electronics/solenoid to work.
We discussed this at length in the past. Without up-to-date knowledge, we can't be sure that all modern expensive ones are non-electronic. As I've said, I believe that an electronically-triggered one has the potential to have much better long-term reliability, particularly as regards maintenance of trigger current. The fact that, as you say, it's probably possible to make electronic ones more cheaply (because 'precision' in the mechanics is not required) does not mean that ones with good quality mechanics cannot be electronically activated - which might well be the best of both worlds (and might well be what some expensive ones are now doing).
Just to throw another clarification/spanner in the works, a footnote to the definition of "function independant of line voltage" in the standards says:
I think the biggest risk here is loss of neutral followed by prying by the curious and untrained.
So does that mean the manufactuers of mechanical mechanisms will over-engineer their devices, or do you think they manufacture to the required specification to meet the standard only, as per the electronic ones?
Quite so. In fact, with TN-C-S, there is virtually no difference - none at all in the network and esentially only the difference between R2 and Rn within the installation. Particularly with TN-S, I suppose that it's theoretically possible that the Zs would be such that the OPD would be just about good enough to provide short-circuit protection but not quite good enough for (earth) fault protection, but that's not going to happen very often.
I think that probably qualifies as a spanner, rather than a clarification, doesn't it. Although it is not totally clear (at least, not to me) as to what it means, it sounds rather like the opposite of what one would expect. One (at least, I) might have thought that an 'auxillary (presumably power) source' would tend to render the device independent of the voltage of the 'primary source'.
Indeed. In realistic terms, it's probably effectively the only risk - for the neutral to be lost and someone to be prying as co-incidenally simultaneous and independent events would surely be 'vanishingly improbable'! However, if the entire installation went dead because of a totally lost neutral, they might well be prying in the CU, where there is scope for them to be prying on the supply side of an RCD - in which case it's presence would be unable to 'protect' them, even if it was able to work!
I think Bernard's point is that non-electronic ones necessarily have to have 'precision mechanics' in order to get the correct trip functionality. However, as I've said to him, there is no reason why having good quality ('expensive') mechanics precludes an electronically-triggered mechanism - which I am inclined to view as the best of both worlds. To essentially be relying on a spring (no matter how 'high precision') to maintain a constant trip current over a period of possibly very many years does not instil me with confidence. However, electronics will nearly always maintain a consistent trip threshold 'for ever', and the solenoid can be 'over-engineered' to the extent that it's almost bound to result in the mechanism tripping once the electronics tell it to, even if those mechanics have got 'a bit sticky' over the years.
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