Non-bidirectional RCD/RCBO feeding sockets, should they get a code C2 with EICR?

[ericmark]

I think it was @JohnW2 who pointed out for the RCD/RCBO to fail it needs to test button to be pressed, while the flow is reversed, but from 10 am to 6 pm today flow was reversed, so there is a reasonable chance of the button being pressed at the wrong time.

I looked at data sheets, non seem to say non-reversible, they only say when it can be reversed, and there are type 'A' which show input and output so the plug in solar website which says

is incorrect. I look at

Round fuse holders, were Siemens not Wylex, and not seen any in the UK, Algeria 1980 loads, as working for a Dutch company, darn dangerous things, as fuse was before the switch, so to change a fuse base it had to be done live.

But it would seem they have translated a German website!

 

[JohnW2]

Fair enough. As an engineer, I too am expected to make evidence based judgements, or present evidence to colleagues who have to make a decision.

I'm pleased to hear that - and one might hope that would mean that you would share some of my concerns about things which appear to be minimally 'evidence-based'.

You seem to be applying the same flawed logic that the vendors of these so called safety covers use - that they prevent a risk.

Not at all. In the absence of any hard evidence (or either harm or benefit), I'm just remaining 'open-minded' - I'm certainly not dismissing the claims that they result in some risks (since they undoubtedly do to at least some extent), but nor am I dismissing the possibility that they might also sometimes reduce or prevent risks. I just don't know (and certainly don't know about the balance between the pros and cons), and I would perhaps have expected you to feel the same, given your experience of 'evidence-based' decisions.

I would imagine that would be heard to come by. The main problem is that the general public aren't likely to report anything, and the authorities are only likely to know if it's serious (e.g. someone is hospitalised.) Also, some of the potential harms would not be related to the previous (possibly years previous) use of these items.

Evidence (for either causation or reduction/prevention of harm) would certainly be very difficult to 'come by' - but, if one believed in evidence-based decisions, difficulty in finding evidence is not really, in itself, reason to jump in one direction on the basis of one's theeory-based opinion.

I think you are more generous to the manufacturers than I am. .... I am really sceptical that someone looked at the standard and consciously designed something with larger pins.

You are quite possibly right. However, again I just don't know - so if you want to go with your own opinions rather than anything based on facts, then I suppose that is your prerogative.

As I've recently written, I think we're now seeing similar with SPDs (with maybe AFDs/whatever 'to come'). Some people seem to be totally sold on the idea that they are 'necessary', seemingly almost totally because of theory-based opinions - despite the paucity of any evidence I've managed to find (and I've looked quite hard) that there is actually a significant 'need' for them.

Agreed. Either that, or the requirement should specify what standard it is required to meet - e.g. by referencing an existing standard for flammability.

Sure, the reference to 'non-combustible' is quite ridiculous and those who wrote it should have known better - as you imply, they obviously should have clearly defined what degree of 'flammability' is required.

However, that's not the main problem with that reg - more important is the lack of significant evidence (that I've seen or heard of) that there is/was a significant need for some higher degree of 'fire resistance' of CU enclosures - particularly given that metal CUs etc. do introduce some dangers.

Unfortunately, we seem to be getting ignored as there's been no shortage of people (myself included) who have raised this - yet there's been, IIRC, 2 or 3 new versions where they've failed to fix this f'up that brings BS7671 and BSI into disrepute.

Rumour had it that it was intense pressure/'threats' from LFB that resulted in the appearance of the reg in the first place - so I suppose the same may be resisting any modification to it?

 

[JohnW2]

I think it was @JohnW2 who pointed out for the RCD/RCBO to fail it needs to test button to be pressed, while the flow is reversed, but from 10 am to 6 pm today flow was reversed, so there is a reasonable chance of the button being pressed at the wrong time.

Yes, in relation to a 'full' solar installation, I acknowledged that above ....

.... One imagines that, in Summer, in an installation with very low background loads, there could possibly be net export for 'a few hours' every day, and it's not impossible that someone could press a test button whilst that was the case.

However, as others have said, with these 'plug in solar' systems, I doubt that their output would be adequate to result in much, if any, export for a significant amount of time.

Returning to the actual 'potential problem', none of us have yet thought of any potential issue (with 'unidirectional RCDs) other than that associated with the Test Button, if pressed for a 'significant period of time'. I suppose a couple of simple 'solutions' to that would therefore be (a) to not fit, or disable, the Test Button or (b) utilise a 'momentary action' Test button, whose contacts only remained closed for a modest handful of milliseconds!

 

[ericmark]

So you think there should be an instruction with plug in solar not to press the test button on an RCD/RCBO when the plug in solar is plugged in, and that is enough?

Maybe it is enough, but goes against the grain.

Remember plug in solar is designed for tenants, do you think tenants will worry about pressing a test button anyway?

 

[JohnW2]

So you think there should be an instruction with plug in solar not to press the test button on an RCD/RCBO when the plug in solar is plugged in, and that is enough? ... Maybe it is enough, but goes against the grain.

Certainly 'better than nothing', given that at least some users would presumably obey the instruction, but I agree that it would fall short of what one really wants/needs.

What I was suggesting were more ways (in addition to those we've already discussed) of manufacturing RCDs which would not suffer from the 'Test Button Problem' during export.

Remember plug in solar is designed for tenants, do you think tenants will worry about pressing a test button anyway?

As you imply, if used by tenants it's probably less likely that they will press the button. However (a) that's no guarantee that some of them wouldn't press the button and (b) there's no guarantee that it will only be used by tenants. However, as I recently wrote, whether such kit will result in export for appreciable periods of time is perhaps a different matter.

However, something has just occurred to me, which I should have thought of before ....

.... do these 'plug-in inverters', like the ones in proper PV installations, shut down immediately if they lose their grid connection? If so, then if the RCD operated because the test button had been pressed, would not the inverter shut down rapidly enough to prevent overheating of the test resistor? If that were the case, would all the interest/excitement about 'bidirectional' RCDs not be unnecessary? Or am I missing something?

 

[ericmark]

.... do these 'plug-in inverters', like the ones in proper PV installations, shut down immediately if they lose their grid connection?

I believe the "proper ones" are designed so over/under-voltage and out of frequency shut down is not delayed, so stop a short blip in the supply causing 1000s of solar panels all disconnecting together which could bring down the grid.

Where the plug in type disconnect faster.

However, it seems this all varies country to country, so for example set to Germany maximum output is 800 watt, but set to France it is 900 watt.

Also, the delay should be over 40 mS so the RCD can trip with a fault before the solar inverter cuts out with installed systems, this is not wanted with plug in, so until the document is unveiled in the next few days, we simply don't know.

 

[JohnW2]

I believe the "proper ones" are designed so over/under-voltage and out of frequency shut down is not delayed, so stop a short blip in the supply causing 1000s of solar panels all disconnecting together which could bring down the grid. ... Where the plug in type disconnect faster.

I'm a little confused by some of that, but do I take it that you are saying that (as I would expect) a plug-in inverter would shut down very rapidly after disconnection from the grid (e.g. due to RCD operation)?

Also, the delay should be over 40 mS so the RCD can trip with a fault before the solar inverter cuts out with installed systems, this is not wanted with plug in, so until the document is unveiled in the next few days, we simply don't know.

Disconnection might take 40 mS, but I think that a very substantial proportion of that would probably be due to the 'mechanical happenings' after the tripping mechanism had been triggered. I might be wrong, but on the face of it I would not have expected that ('irrevocable') 'triggering' to require the residual current to flow for more than one cycle (20 mS) at most, more likely one half-cycle (10 mS) or less - in which case there would be no need for inverter shutdown to be delayed beyond those periods of time for normal RCD functionality to remain.

 

[ericmark]

My error "shut down is not delayed" should have been "shut down is delayed" sorry.

 

[JohnW2]

My error "shut down is not delayed" should have been "shut down is delayed" sorry.

Yes, I rather suspected that my confusion was due to some disobedience on the part of your typing fingers

However, what about the rest of what I wrote?

 

[SimonH2]

If the socket is such that that can be done with one of these devices, the same could presumably also be achieved using a BS1363-compliant plug, and even the NHS could not 'ban' the use of them!.

Actually no, a standards compliant plug cannot be inserted upside down in a standards compliant socket - that's part of the standard (indirectly.) Two factors at play :
* A plug is rigid, so can't be bent to allow insertion upside down using just the "earth" pin to open the shutter - the (msotly) soft plastic covers can.
* If the socket is standards compliant, the size above the earth pin is such that the L&N pins will foul before the earth pin goes very far into the socket. However, there are some extension leads where they are undersized and allow this - but then they are not standards compliant.
So just the fact that most of these covers are made from (relatively) soft plastic creates a new risk - that with little effort they can be forced in upside down, will bend to allow it, and will defeat the built in protection from the shutter.

I'm pleased to hear that our opinions are the same about that. The reason we both have that opinion is presumably that neither of us has seen any reasonable evidence that 'non-combustible' CUs would offer a significant benefit (let alone 'necessity'). However, if we were presented with reasonably strong evidence that there is a benefit, then we hopefully would (should) consider changing our opinions,

Indeed. But one opinion I do have is that many plastic CUs would comply with a reasonably worded requirement based on some existing standard. We've had "self extinguishing" materials for a long time, and we treat non-ferrous back-boxes as "non combustible" to meet other parts of the regs

However, as others have said, with these 'plug in solar' systems, I doubt that their output would be adequate to result in much, if any, export for a significant amount of time.

Don't forget that they only need to reverse the power flow in the one circuit. So quite possible to have reverse power flow on (say) an upstairs circuit with no loading, while there's a tumble drier going downstairs on a different circuit.

Something else that doesn't seem to be getting discussed is that of how the embedded generation might affect the ability of the RCD to protect against (say) a touch fault. Don't we prohibit connecting an inverter where it shares an RCD with other power using equipment for that reason ? Though I guess that's a different large can of worms

 

[ericmark]

However, what about the rest of what I wrote?

I have read about the changes in the way inverters react when we have a power brown out etc. And it seems it has changed to stop a domino effect. However, exactly what those changes are I am not sure.

With 50 Hz that's 10 ms between each peak.

But the time between losing supply to disconnection is less important with installed solar as to with plug and play, and we can expect to see different times between the two.

We see there is a difference between France and Germany, with France allowing 900 watt and Germany 800 watt, so we need to accept their may be a different set of limits with ours. It seems setting the country to France allows one to export more, and one wonders if the user should have that option?

But in 4 days we shall know, I think we can wait that long.

 

[JohnW2]

Actually no, a standards compliant plug cannot be inserted upside down in a standards compliant socket - that's part of the standard (indirectly.) Two factors at play :
* A plug is rigid, so can't be bent to allow insertion upside down using just the "earth" pin to open the shutter - the (msotly) soft plastic covers can.
* If the socket is standards compliant, the size above the earth pin is such that the L&N pins will foul before the earth pin goes very far into the socket. However, there are some extension leads where they are undersized and allow this - but then they are not standards compliant. So just the fact that most of these covers are made from (relatively) soft plastic creates a new risk - that with little effort they can be forced in upside down, will bend to allow it, and will defeat the built in protection from the shutter.

I've been trying to avoid much discussion about 'details' (particularly about 'what is theoretically possible'), since I think that detracts from my main point - which is that, particularly when 'major decisions' are to be made (like 'to ban' something - or, at the other extreme, to 'require/demand'something), those decisions should be based on information/data/evidence about what is actually seen to happen, in practice, in the real world - rather than considerations of 'what is theoretically possible'.

Having said that, to briefly remind you of something I've written in the past as regards 'inserting plugs upside down', what BS1363-2 requires (of sockets, include those in 'extension leads) seems (at least to me!) to be rather (very!) odd ...

The only requirement regarding placement (relative to 'edge' of the plate/whatever) of the 'apertures' to receive plug pins appears to relate to the L& N pins, but not the earth one .....

... as I've said before, unless I'm missing something (like a corresponding requirement relating to the earth pin receptacle), that appears to mean that it would be perfectly possible to have a compliant socket (with earth pin 'receptacle' fairly close to edge) into which the earth pin of a compliant plug could be inserted with the plug 'upside down' if the socket were attached to a surface pattress box or was one of the outlets of an 'extension lead', hence allowing something like this (as mentioned by you) that I once illustrated...

Indeed. But one opinion I do have is that many plastic CUs would comply with a reasonably worded requirement based on some existing standard. We've had "self extinguishing" materials for a long time, and we treat non-ferrous back-boxes as "non combustible" to meet other parts of the regs

Quite so. Even if there were a significant 'need' for an improvement in the fire resistance of CU enclosures (which I personally very much doubt), as you say there are plenty of non-metal materials that could have been specified as being adequate/satisfactory - and that would have avoided the (I personally believe very irresponsible) unnecessary introduction of an increased risk (albeit very small) of death or serious injury which has resulted from the reg as currently written.

 

[JohnW2]

But in 4 days we shall know, I think we can wait that long.

I'm not convinced that it would be wise for you to 'hold your breath'

 

[ericmark]

I'm not convinced that it would be wise for you to 'hold your breath'

Neither am I, a month as a unit of time, unless specified otherwise, is no law 28 days. In the same way as a ton is 20 cwt, you have to say metric ton, if that's what you mean.

As to BS 1363, BS 7671, G98, G99 etc. These can all be altered, but as far as identifying unidirectional RCD/RCBOs that remains a problem. I can't see a simple way to tell the public you can plug in with this type A but not this type A.

I do see the regulations do say with the note, that they must be marked, but in and out is normally hidden by the CU cover.

I remember seeing one make with the marking on the face seen by user, and tried to find it as an example, doing this hunt, I noted how many type A RCBO of the short design were unidirectional.

With a RCD we could easy mount it either way around in a board, if it physically fits

when horizontal the direction of writing means nothing. But the neutral tail on the RCBO means we don't really have an option of which way around.

So we just hope that all unidirectional devices do have in/out marked.

 

[JohnW2]

...
View attachment 415412 I do see the regulations do say with the note, that they must be marked, but in and out is normally hidden by the CU cover.

That's a new one on me. Where did it come from, since I can't find it in any version of BS7671?

So we just hope that all unidirectional devices do have in/out marked.

No matter what you (or 'we') may 'hope', and as I've said, it it is surely the case that there are countless millions of RCDs (presumably 'unidirectional') out there in service (including well over a dozen in my house) which do NOT bear any such marking, isn't it?

For that reason, I find it hard to understand how any 'regulations' about plug-in inverters could possibly address this issue - if many/most people don't know (and probably can't ascertain) whether their RCDs are unidirectional or bidirectional, they can hardly be expected to comply with regulations that would require that knowledge ?!