Explain why RCDs fitted into extension leads or incorporated into plugs are forbidden

I think we are on the same page technically, but not approaching from the same end.

Under what conditions is it sensible to ban or remove RCDs inline with plugs or extension leads ?

1) when they cause a problem, false trips etc.

2) when, and only when, you can be sure, really really sure (!) , that the  device or lead will only ever be plugged into an already RCD protected socket.

As I said at the top, ideally they  should not be relied upon as the sole means of protection but that is not the same as demanding to cut them off willy nilly.

1 is clear cut

2) less so.
Firstly if you are dead certain there is already a working RCD in the line,  then you may not need them, but does it do any harm  to leave them in ?

Secondly, are we that sure there will always be an RCD upfront  if it is not a TT building ? The evolution of the regs and the time delay between changes and universal implementation is much longer than some authors on here imagine.

So a reg changes.

In the immediate year or two a few folk will carry on with projects already started and maybe the odd one who does not even know.  For a few more years the chancer types who do know really, but are happy to ignore it will offer cheaper jobs that use up old stock, especially at the shallow end of the cash job/ minor works market.

(some folk still have red and black T and E on part reels from nearly 20 years ago )

So I expect new socket circuits to be RCD protected, and most (but maybe even then not all) new additions to existing to have an RCD, but really a large fraction (maybe 75% plus of all wiring in use) will be pre-existing. These will only be updated for sure on an inspection fail that demands a change, so a C2 or C1 report, or in a private house when changing the CU.

I respectfully suggest that the average regs change to full implementation, the time delay should be measured in decades and perhaps quite a few of them.

As a non RCD but related real example, I live on a 1970s housing estate where none of the houses had lighting circuit CPCs when built, even though by then the regs requiring that had changed some years before. So, even now based on the neighbours I have visited, still less than half have been rewired to achieve this by 2022, though many who have new-ish plastic  CUs have an RCD for the lights and a 'no CPC' notice, so some nod to modern ways, safer than original,  but not compliant.  I do not live in some sink estate, or miles from civilization,  this is a well to do home counties market town, so I assume there are far worse out there.

Change is not measured in mere years.

And then there is the slight but non zero risk that the fully compliant RCD in the CU does not actually fire on demand, but for one reason or other sticks.

Still want to take the RCD plugs out of service ? I'd not want to justify that position.

Mike.

mapj1 said:

Still want to take the RCD plugs out of service ? I'd not want to justify that position.

Or similarly, when I change my CU (progress is being made!) should I replace the RCD sockets which go back to 15th Edn?

Chris, you will almost certainly have to remove any sockets with built in RCD protection, because if anyone presses a test button to test a socket RCD or just to turn the socket off I can almost guarantee the circuit RCD will trip in the consumer unit as well.

A bogof test button, nice. If I were Chris I wouldn't replace them until the tripping of the main RCD was verified. And even then I would consider whether it was a nuisance or not, Chris would probably go for all RCBO anyway, so the benefits of having two RCDs in series, thinking redundancy, might outweigh the nuisance.

It’s even more fun if the installation has an upfront 100 mA RCD and someone has fitted a SRCD socket with a built in RCD, then you need to swap the upfront 100 mA to a 30 mA.

Thank you, Sparkingchip, I hadn't thought of that.

Pressing the test button every 6 months wouldn't be a problem, but we also have an RCD protected FCU which supplies the pump of a small fountain. In effect, the test button is the "off" switch so that would be operated on a daily basis.

And yes, the CU will be all RCBO (and will probably incorporate an SPD).

Chris Pearson 

SRCD are generally referenced to earth with a fly lead. 

Chris Pearson 

SRCD are generally referenced to earth with a fly lead.