Poll: Compliance of Sockets Circuits

[JohnW2]

This is from BS7671, and where the 30% limit for leakage current is from: .... 30% of a 30mA RCD being 9mA. .... This is a sample of leakage currents for a selection of equipment. ....

Yes, I am aware of all that. [it's interesting that the second document you quote indicates a number of types of loads, including cooking appliances, which, individually, have a 'maximum leakage of 10mA - and 10mA is, of course, more than 9mA]

531.3.2 first appeared in the 18th edition in 2018. ... Section 314 which is Division of Installation has been in there for decades, since the 15th edition.

Indeed - but even 531.3.2(i) contains the words "likely to occur" - and the "such currents" mentioned in 531.3.2(ii) are presumably those "likely to occur" ones mentioned in 531.3.2(i).

The relatively recent prevalence of everything having electronics inside, and specifically switching power supplies, has significantly increased the leakage current for a very large number of items, including those which previously had little or none. Modern homes typically have vastly more items of equipment than those of only a decade ago.

Whilst what you say about the proliferation of things like switching power supplies is certainly true, I cannot help but wonder whether this is not a case of 'theory over-riding experience and common sense'. That is certainly the case with my personal experience. I have some circuits which have many (a dozen or more) connected items with SMPSUs (quite apart from whatever might be connected to other circuits protected by the same RCD) and I know that has not resulted in problems due to earth leakage currents - since I have virtually never experienced any operation of an RCD 'without good reason'.

There is no reason why my experience should be unique, so I wonder how many people actually have experienced RCD trips which they think may have been due to excessive 'leakage currents in normal operation' of connected loads?

Kind Regards, John

 

[EFLImpudence]

You would have to ask flameport that question - since he used the term, I assumed that he meant what he wrote (per BS7671 definition).

No, I was referring to your poll question.

I thought you were trying to catch us with the (apparently) new definitions of compliance and conformity.

 

[JohnW2]

And a related question is what are the actual real-world values of earth leakage from appliances, both when in use and when not in use.

Flameport has posted some figures, but they only relate to "allowed" and "maximum" leakage figures for various types of load and, as you imply, give no indication of what the real-world figures are.

As I've just indicated, my experience suggests that many iof these loads must, in the real world, have much less leakage that the maximum 'allowed' figures - otherwise, even if they didn't trip until there was nearly 30mA of total leakage, I would probably be suffering from RCD trips all the time - yet I virtually never do. As I've just written, I do suspect that 'theory is over-riding experience and common sense'.

We don't design installations to support the theoretical maximum load of the equipment therein, so should we design them to support the theretical maximum earth leakage.

Quite so. In fact, I see no reason why we should not just go by the word of the regs and design circuits to support "the theoretical maximum earth leakage" that, in our judgement, is likely to occur.

Also worth noting that the lot of smaller SMPSUs are class 2, so don't contribute to earth leakage unless something makes a connection between their output and ground.

Good point. Whilst, as I've said, I have a large number of SMPSUs, many connected permanently, the great majority of them are Class II.

Kind Regards, John

 

[JohnW2]

No, I was referring to your poll question. I thought you were trying to catch us with the (apparently) new definitions of compliance and conformity.

My poll question was inevitably not fully clear, because of the character count limit, but I thought you would have understood that the reason for my posing it was because flameport had essentially suggested, in another thread, that dual-RCD CUs are 'non-compliant' - and since it was that term he used, as I said, only he could tell you whether (per BS7671 definition) he meant 'non-compliant' or 'non-conformant'.

However, my concern (as expressed in that other thread) is that I feel sure that most people reading what he wrote will assume that his 'non-compliant' means 'non-compliant' (by BS7671 definition) - which, as I implied, I personally feel is potentially misleading.

Kind Regards, John

 

[JohnW2]

And before that, was the split load consumer unit, with one RCCB usually controlling all the socket circuits (and shower), and the unprotected side usually controlling the lights.

Indeed so - I installed some of them myself. However, as you go on to say, in terms of 'RCD protection' they were adequate in terms of the then-prevailing regs.

However, the issue we are now discussing is nothing to do with the adequacy of 'RCD protection' - we are talking about the theoretical risk that having too many circuits protected by the same residual current device may result in 'nuisance tripping' (which is only very rarely 'dangerous') due to accumulated leakage 'in normal operation' of many protected loads.

Kind Regards, John

 

[EFLImpudence]

My poll question was inevitably not fully clear, because of the character count limit, but I thought you would have understood that the reason for my posing it was because flameport had essentially suggested, in another thread, that dual-RCD CUs are 'non-compliant' - and since it was that term he used, as I said, only he could tell you whether (per BS7671 definition) he meant 'non-compliant' or 'non-conformant'.

Ok. In that case I vote no as not potentially dangerous.

 

[JohnW2]

Ok. In that case I vote no as not potentially dangerous.

Fair enough. Thanks.

However, do you even believe that it is 'non-conformant' (because I personally don't)?

Kind Regards, John

 

[securespark]

I think this is one of those situations where things are open to an individual's interpretation, plus the fact that the regs is a bare minimum and can be "bettered".

 

[AndyPRK]

Lots of mistakes in here, so I’m sure you guys will love to point them out. (bit of a sport on here !)

 

[EFLImpudence]

However, do you even believe that it is 'non-conformant' (because I personally don't)?

No, neither do I.

 

[JohnW2]

I think this is one of those situations where things are open to an individual's interpretation, plus the fact that the regs is a bare minimum and can be "bettered".

Indeed. In fact, it's not so much a matter of 'interpretation' as of judgment. As I've said, the regs were are discussing all talk in terms of what is "likely" to happen (in terms of loads, leakages or whatever), and that clearly is a matter of a designer's judgements.

However, I personally think it's wrong (and potentially misleading) for someone to talk, in general terms, about something being 'non-compliant' when that conclusion results from their own personal opinion/judgment as regards what is "likely" - particularly given that judgements about 'likelihood' will (should) vary between situations, rendering blanket asserts inappropriate.

Kind Regards, John

 

[JohnW2]

No, neither do I.

I'm glad you agree.

I see that, so far, only one person other than the one who caused the question be asked has voted 'Yes'.

Kind Regards, John

 

[ericmark]

@AndyPRK video says what I feel, except not so sure if a court can blame an electrician for fitting a twin RCD board if it trips and Mrs X falls down the stairs. If your tests show less than 9 mA drain to earth then you have shown you have taken reasonable steps.

However you need to show you did the tests, and the installation certificate as it stands does not show you have taken reasonable steps to ensure during normal operation 15 mA will not be exceeded.

This may seem an about turn for me, as I have always said RCBO is the way to go, and I still think that, but the question is can you condemn an installation which only uses two RCD's?

If there is a question on the installation certificate which asks back ground leakage, then you can say tested it was only 5 mA and clearly some item not in use when tested had resulted in the trip. But if you can't show it was tested, how can you show reasonable steps were taken?

If the lights fail, I would stop moving, be it on flat or down stairs, I would wait for my eyes to adjust, and only after that would I proceed, but would proceed with extreme caution, I have a rechargeable torch on the landing which will auto light with a power cut, however it will not auto light if only the lights trip, to light the sockets must trip.

If half way down the stairs when lights fail, I have two options, return to top and remove torch from holder which will auto turn it on, or continue to bottom and into living room where there is another torch which will auto light with power cut or when removed from holder or when it detects change in IR signal, same as one top of stairs.

These cost less than £20 and allow me to investigate why lights have failed. If the lights are only circuit to fail, then the Nest thermostat will also activate and give light. I know battery backed but not tested to see if it turns on with loss of power.

But as has been pointed out to me many times by John does not matter how many RCBO's fitted a general power cut means no lights.

So risk assessment is down to getting a shock due to some fault in a socket circuit leaving the injured also in darkness.

So we want in every area the lights and sockets to be supplied from a different RCD or for emergency lights to be fitted. So if the circuits can be arranged so lights are never on same RCD as power and back ground leakage does not exceed 9 mA then two RCD's are OK. In most installations this is not possible so it needs more than 2 RCD's. But not all, so have to select depends.

 

[JohnW2]

... not so sure if a court can blame an electrician for fitting a twin RCD board if it trips and Mrs X falls down the stairs. If your tests show less than 9 mA drain to earth then you have shown you have taken reasonable steps.

I think the testing is a bit of a red herring, since there really is no way in which an electrician can undertaking any meaningful tests...

... even if the electrician asked the householder to 'plug in all their most leaky items' (which I very much doubt that (m)any electricians do), the result proves little, since there is no telling what might be plugged in 'tomorrow'.

As you go on to imply, if we are talking about people falling down stairs because they get 'plunged into darkness' then it might be more credible to suggest that a court might find against an electrician who failed to install (or, at least, advised on the need to install) emergency lighting).

This also illustrates that one should probably not be too obsessed with "compliance with the regulations" as a means of evading liability - I would imagine that a court could, if it so wished, argue that, even though emergency lighting is not required by the regulations, "any reasonable man would know that sudden loss of light might cause someone to fall down the stairs".

Kind Regards, John

 

[Risteard]

Lots of mistakes in here, so I’m sure you guys will love to point them out. (bit of a sport on here !)

The title's wrong for a start. An RCBO is an RCD, whereas he is intending to compare and contrast RCCBs and RCBOs.