Your feedback on regulation issues

Your voice is heard! In fact, you may have much more support than you think, it is one of the reasons why this forum is so good. People on JPEL/64, The IET policy committee etc. regularly read this, and some write on it too. That is why I ask for evidence of certain things, but unfortunately, that is not very forthcoming, and I need documented incidents, with pictures if possible, to pass to the relevant people who can make a difference. This is your voice, and it is quite powerful!


The point of this is to make your lives easier, and safer for everyone. It should not be necessary to read a set of manufacturers' instructions which try to change the way the regulations are designed to be applied or to make new ones to suit marketing policies. This thing about RCDs and current ratings is very difficult to implement in existing installations and even more difficult to inspect because at the time of installation these instructions were not written at the time of installation!


Manufacturers instructions are a very bad idea, because they change with time and cannot be referenced to the actual installation. The only way to do this is very bureaucratic and would be a "Technical construction file" or TCF, which contained all the design data in minute detail, including the manufacturers' instructions used for installation. If such a file were not present the installation would have to be condemned as dangerous for continued use, or inspected to the latest instructions for each product, which may well not exist anyway. This is the route used for complex products in other areas, for safety and EMC for example, but it is very expensive. It provides a method that single products need not be inspected and tested to every detail of regulations, when they are one-off or low volume manufacture.


I think that 75% of domestic installations would immediately fail completely, although not damaged and perfectly safe. Manufacturers would rub their hands with glee, and look for a sales bonanza as all these installations were "updated". It would increase costs considerably and many installations would have to be replaced completely. But why, we don't really have a problem do we? The size of the main fuse up to 100A has always been considered safe and satisfactory for CUs, and there is no evidence that it is not. These new regulations in the 18th (which slipped in as UK only) have very far-reaching consequences which may not have been foreseen by the members of JPEL/64, at least not enough to have stopped it in a vote. You may say "conspiracy theory" but the result is not is it?


Regards to everyone, and please send any evidence, davezawadi (at) yahoo.co.uk.

David CEng etc.

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The size of the main fuse up to 100A has always been considered safe and satisfactory for CUs, and there is no evidence that it is not. These new regulations in the 18th (which slipped in as UK only) have very far-reaching consequences ...

David,


All consumer units stated as suitable for 100 A supplies in the UK (called CDB's - customer distribution boards - in the standard) should comply with Annex ZB of BS EN 61439-3, which contains the requirement for testing from the 100 A BS 88-3 supply fuse, with fault currents of 16 kA, in this arrangement.


So I think that's covered (and also the use of 6 kA rated mcb's and RCBOs in these CUs), as the national test covers this?



Regarding the question about "maintenance replacements", Regulation 536.4.203 effectively says use the manufacturer's recommended products, or you take responsibility (of course, how could a manufacturer of a consumer unit vouch for another manufacturer's testing)?

Yes Graham, I know that BUT the Manufacturers are trying to say that if the MCBs after an RCD rated at say 63A total more than 63A they are non-compliant. This is a significant issue, in that both the manufacturers' instructions and the type testing results and specification are at odds with one another, and they are saying that the RCD needs protecting at its rated current with a CPD (usually the main fuse). This is because the instructions have been "adjusted" recently to make the fitting of RCBOs mandatory to allow this protection if 100A RCDs are not fitted throughout. In fact, I have not yet got a copy of the instructions, so this is slightly secondhand, but SparkingChip has posted it as such. I await the full evidence if someone would like to post/send me a copy from any of the BEEMA companies CU instructions, which apparently are all identical about this requirement. Effectively it outlaws any kind of diversity in the CU unless final circuits have RCBOs or 100A RCDs, which is not what they actually sell in split "filled" units! The alternative is that the supply cannot have a 100A main fuse, which does not comply with BS EN 61439-3.

If correct, that is interesting.

If I understand what David is saying, the manufacturers require that the sum of the ratings of the MCBs after each RCD is no greater than the rating of the RCD. So why is it that the sum of the ratings of the RCDs may exceed that of the main switch? (In which case, the sum of the rating of the RCDs may also do so.)


It is also counter to 314.1. Starting from scratch, in let's say a 3-storey house, I might want one circuit for the smoke alarms and three for the lighting (one per floor). One would suffice, but with no difference in load, we have 1 x 6 A or 4 x 6 A MCBs. Similarly with 4 socket circuits (one for each floor with a separate one for the kitchen) we have 4 x 32 A, but it would be bonkers to suggest that this means that the load would ever be 128 A, especially in a modern well-insulated home.


I really must upgrade my own CU: after nearly 40 years of use, it's a wonder that it has been able to cope with 300-odd A of MCBs. ?

Hi Chris


Have you installed a CU recently? I want a scan or original of the supplied instructions for research into this, and I don't want to buy one I don't need at the moment. It needs to be from a BEEMA member manufacturer, and probably packed recently, not old stock?

davezawadi (at) yahoo.co.uk!

Regards

David

David - I take it you're referring to 536.4.202.


That seems to be just part of huge re-write of section 536 for the 18th Ed. I can't help wondering if such vast changes don't originate with JPEL/64 but as just copies of chunks of some upstream standard (IEC/HD 60364 or possibly bits culled from BS EN 61439 itself) - in the same way that A721 would seem to have been plagiarised from BS EN 1648. If JPEL/64 works anything like any committee I've known it would have taken them decades to come up with so many words themselves. Even the 200 numbering only means it's UK specific, not necessarily JPEL/64 origin - many EN standards have country specific conditions and appendices so it might just be a copy-down from elsewhere. Certainly JPEL/64 should have yea/nay'd it in principle, but if it is derived from some 'higher' standard their choices might have been limited.


In any even the lack of obvious overload protection for RCCBs in (especially split load) CUs was a bit of an anomaly - we'd never put a 63A device in the middle of a 100A circuit if we were just wiring discrete separately enclosed devices together by normal BS 7671 rules. It was only previously acceptable because the whole CU assembly was covered by other standards and so outside the scope of BS 7671 (other than the choosing of it). Even now there still seems to be a get-out clause of following manufacturer's instructions (so presumably in theory they could still specify that a 100A fuse is OK for their 63A RCCBs if they want - even if BEEMA members choose not to do that).


I guess another consideration is that the nature of loads on CUs is changing - a lot more will be getting EVSE and heat pumps connected to them which are likely to have rather different characteristics (larger currents and long durations) compared with many traditional domestic loads which tend to be either low current or short duration (off-peak storage heating being the one obvious counter example, but that's come with warnings about loads on CUs for donkey's years). Manufacturers (incl. BEEMA) might (reasonably) be trying to position themselves to avoid anticipated future problems.


Or I might have the wrong end of the stick (agin)

    - Andy.

Here is the BEAMA guidance.

Here is Hager's guidance.

Here are Hager's installation instructions.


It all seems perfectly reasonable to me. The easy approach is to match the upstream OCPD with each RCD because you then do not have to consider diversity. The alternative is to do your diversity calculations (100% of the highest rated circuit + 40% of each of the rest) and select the current rating of the RCDs accordingly. Similarly, the Hager boards have integral SPD, which saves the bother of doing a lightning risk assessment.


So in fact all that Hager seems to be saying is, "Save yourself a lot of bother by fitting our CUs."


How many electricians pay much attention to the usage of each circuit? I went through this exercise when designing my step-daughter's installation - her husband wanted plenty of division in order to avoid the effects of "nuisance tripping". So the utility room sockets may at times be heavily loaded with cloths washer, dishwasher, and dryer; but the kitchen will be lightly loaded with only kettle and small appliances. It was a right old palaver, which I wouldn't want to do on a regular basis.

I have looked at the information provided by the references from Chris above, and they do not make much sense. They come up with the "magic" diversity equation, in some way supposed to describe real diversity decisions. The problem which it does not consider is this:


Real diversity is not about how many circuits are installed, it is actual loads' characteristics that matter. It seems that Hager (and therefore possibly BEAMA as a whole) do not understand this. If I fit 2 ring circuits to a house, does the actual maximum demand double? Of course not! It is true that I could then use 7 or 8 electric fires of 3kW at the same time and for long periods, but the house would have to be very large or become far too hot. I know that I have been commenting on diversity quite a lot recently, but it is badly understood by many, and depends on load, period of use, and its AVERAGE power consumption over a long period. Because all these things need Engineering Judgement which is often in short supply, many "rules of thumb" have been invented, and over time, seem to have received unwarranted status.


The instruction from Hager seem to be designed to sell either RCBOs or higher rated RCDs, or perhaps to limit the number of final circuits provided which surely is counterproductive to their sales. The references used from BS7671 are taken out of the full context, and used as reasons to change our use of the Consumer unit. I would say that it is trying to solve something which is not and never has been a problem, but the important bit is that is a MISUSE of the manufacturers' instruction (MI) clause in BS7671. I think that it is trying to change BS7671 via the back door for manufacturer benefit, and at best is highly confusing to Electricians and particularly Inspectors, who have to decide if the MI now need many installations to be given a C2 because the MI say that the installed CU ratings are inadequate. This is the worst possible outcome because they are generally perfectly satisfactory, and have been for a long time, but the MI have to be taken as fully retrospective, or if not at the Inspectors risk! Repairing an existing installation may be quite difficult as it may require further splits to the CU to 3 RCDs, or its replacement. This means that all the latest regulations on SPDs AFDDs etc may come into force as a result of the change, which will be very expensive indeed, and at the stroke of a pen in the MI.


Overall this is highly undesirable to both the industry and the consumer, and there is no significant benefit to anyone is there (except BEAMA members perhaps)? Remember that the average power use in each house is less than 2kW, and most of the time very low. This is the real diversified figure for around 20 million installations. CU fires are not and never have been caused by overheated RCDs, just loose connections caused by poor screw quality and inadequately designed terminals.

For what  it is worth, the new Wylex 'NM range'  CU I had my head in this weekend came with a leaflet that has no such caution - just  a note that
'All RCDs must be used in conjunction with a 50A max  rating B or C type MCB.'  

Which apart from the rather "translated German" word order, and seemingly precluding the plurality of MCBs normally seen supplied by one RCD,  does not say anything about total loads, or indeed the rating of the incoming supply fuse. Unless of course  it was supposed to  mean the incoming protection should be a 50A MCB, but it does not say that, clearly. Now I have fished it out of the bin bag, I can post a picture of the leaflet later on tonight if that helps, though the instruction leaflet is copyright 2012 so there may be a newer version coming soon, if this is the old one- I have no idea how long this CU sat on the wholesalers shelf before I got it.

As it happens I am fitting the version that is a dual tarriff all RCBO board, as it is my own, and that approach appeals both to my engineering judgement.and SHMBO, but the instruction leaflet seems to be universal.