just for interest (perhaps) OCP for RCCBs

So as  I read it, the organization of the very manufacturers who only a few years ago were quite happy to sell us their split load consumer units with two 60A RCDs in, knowing these were  often  to be fed from a 100A cut out, now say they should have been 100A RCDs. 

Hmm. 

Good job RCD fires are so rare ?

MPJ

Oh dear, here we go again, more new CUs because the regs changed! Except that they did not, and this manufacturer's instruction is spurious. The next thing will be that the type-tested CUs with 2 60A RCDs, which should have tested them with a 100A fuse in place, cannot have been completed properly or passed the testing, which does test everything at the rated current of the supply fuse! It looks like an attempt to sell RCBOs to me, I wonder how they survive a 7kA Earth fault? They still have to break 7kA even if rated at 6A.

On a better note, most properties have 60A main fuses, but as the inspector cannot tell because they are sealed, we now need to follow a new manufacturer's instruction based on a BEAMA leaflet, after the fact.

This will come up for much more discussion in JPEL/64 because they knew what BS7671 actually said and failed to provide the correctly rated product but sold it as compliant. A lot of replacement CUs free of charge very soon I should think, this is blatant misselling.

Another thought, perhaps they are worried that 100A through a 60A RCD will not meet the tripping specification? This is unlikely although the transformer wires may get a bit hot. This might cause a bit of a meltdown somewhere but burning would be unlikely, and there is not likely to be enough temperature rise to change the magnetic properties. I wonder if this is a new kind of failure?

Well to admit, this rccb ocp specific detail without diversity allowance had escaped me.

It does seem to be, for dual+ RCD boards, that

• sum up the MCBs and ensure ≤=  RCD rating, or
• ensure the RCD rating is ≥= OCPD protecting it/the board, or
• check that the manufacturer is ok with the RCD OCPD combo if above not met

is the order of the day, or something like that .

Or just use all RCBO  ;-)

18th Edition updates:

BS7671 (536.4.202)

However, overload protection shall not solely be based on the use of diversity factors of the downstream circuits.

To achieve overload protection of RCCBs or switches, the rated current of the OCPD shall be selected according to the manufacturer's instructions.

davezawadi (David Stone): 
This will come up for much more discussion in JPEL/64 because they knew what BS7671 actually said and failed to provide the correctly rated product but sold it as compliant. A lot of replacement CUs free of charge very soon I should think, this is blatant misselling.

I am still surprised, and slightly shocked, that the Manufacturers ‘got away’ with supplying combustible enclosures, when the British Standard said they should be ‘non-combustible' (or similar wording) when they made plastic enclosures.

I don't recall any Manufacturers apologising, and offering to replace them with the correct item, made to the British Standard, the originals were sold as.

Perhaps the R.C.D. makers are worried about the higher new long duration loads caused by electric vehicle charging, heat pumps and all electric homes proposed by Boris.

Z.

they will not be worried, the 12month parts only warranty will have long lapsed by now, they will be thinking of the aftermarket update sales to sell uprated RCDs, or better still to kid folk that you have to keep renewing your CU with the same frequency some folk  change their  cars, rather than  only when you change your house by adding to it..

Mike

Don't worry. When you have to change your type AC RCD to a type A one, because the boiler, or hob, or WHY requires it, you can upgrade the current rating at the same time.

And those internal tails are rated at? ?

Humm it sounds like a bit of smoke and mirrors on this one. Applying normal BS 7671 rules for overload protection would mean that you wouldn't normally rely on assumption of diversity to provide overload protection, but would need a suitably rated protective devices (either upstream or downstream).

That didn't happen with RCCBs inside CUs not because of any gap in BS 7671 as such, but because the internals of equipment subject to other standards (such as BS EN 61439 for CUs) is covered by those standards and not BS 7671. So BS 7671 would apply if you were putting an an RCCB in its own box, but what happens inside a CU marked ‘max load 100A’ is down to BS EN 61439 alone. I might suspect there's been an underlying change in BS EN 61439 which has driven all this.

I wonder if the corresponding BS 7671 change (no doubt copied down from IEC/CENELEC) is due to the tradition in other countries of treating a CU/DB as just an enclosure into which the electrician is expected to assemble on-site whatever component parts they think best for that particular installation, from whatever mix of manufacturers they prefer. It's almost as if the UK manufacturers insistence on treating an entire CU as a ‘type tested assembly’ which can only be configured according to the manufacturer's instructions has come back to bite them.

   - Andy.

mapj1: 
 

they will not be worried, the 12month parts only warranty will have long lapsed by now, they will be thinking of the aftermarket update sales to sell uprated RCDs, or better still to kid folk that you have to keep renewing your CU with the same frequency some folk  change their  cars, rather than  only when you change your house by adding to it..

Mike

I was thinking that any future legal claims for dangerous occurrences may still happen even if the product guarantee has expired. 

Z.