Sorry I was not taking a shot at you, more to point out that the removal and reinstatement of RCD sockets and fused spurs to 7288 in BS7671 has nothing to do with extension leads anyway.

(What does get my goat is to do with ivory towered compartmentalization of something that should be better joined up. There are far too many standards, far too many committees, spending a lot of time either undercutting each other, or deciding that things they do not want to think about are out of their scope, or failing to liaise, and they do not fit well with each other. And the result is very expensive, not very informative, 'standards'.)

M.

If I were advising on such a policy, I would be highly likely to begin with the opinion that BS 7071 (because of its age) would cover only Type AC RCDs, and considering the latest knowledge that we have about those devices ("state of the art knowledge" that we are required to consider in risk assessments) ... that they ought only to be used except for purely resistive loads, and even then only where those loads are "fixed", i.e. not portable, socket-outlets, etc. It's also highly unlikely products to BS 7071 alone would have undergone EMC tests for the RCD function (although it's not beyond the possibility that a responsible manufacturer would in fact run additional tests).

Based on that, I think it is arguably the right thing to do, to enforce this policy until BS 7071 is updated to account for Type A RCDs and EMC testing as with the other RCD standards.

Sparkingchip said:

But now they are, which again you should know. 

Although, they would have to be Type A to meet the requirement in Regulation 551.3.3 that Type AC RCDs may only be used to supply fixed equipment (and even then where it is known that the load current contains no DC components).

And it seems that BS 7071 RCDs are likely to be Type AC (the standard has not been updated since 1992).

I've been following this discussion with interest, I'll admit this is waaay outside my area of expertise which is why I'm finding it interesting! I'm just trying to get my head around the point Mike makes above in the context of this discussion: "should not normally be relied upon as the sole means of protection", on the face of it this seems a reasonable position to take - they may not be perfect but at least they are narrowing another hole in the Swiss cheese (i.e. better than there just being a standard plug on the extension lead). Or have I got this wrong and is there a reason why these devices in this application could be actively dangerous, i.e. degrading protection, as opposed to not necessarily providing the safety function expected?

It's a genuine question as it's been years and years since I last looked at RCD technology, and I'm intrigued.

Thanks,

Andy

Andy Millar said:

Or have I got this wrong and is there a reason why these devices in this application could be actively dangerous, i.e. degrading protection, as opposed to not necessarily providing the safety function expected?

Andy Millar  The issue is that Type AC RCDs may not work at all if there are DC residual currents.

Added to that, health & safety guidance (including that published by HSE) recommends the use of RCDs - but what's the point of doing that if the RCD may not operate.

BS 7671 now prohibits Type AC RCDs for general use, and therefore if a work activity demands an RCD, then one ought to be provided, but at present that can't be via an extension lead.


So, I can see the point of this, although I agree we are only commenting on one statement in a company policy or risk assessment, not the whole thing.

So, provided the policy states RCDs should be provided by other means to ensure at least Type A RCDs are used I support it.

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

I might suspect that the thinking is somewhat simpler - from an electrician's point of view all wall sockets (≤32A) should have 30mA RCD additional protection - so given that there should be no need for extra RCDs downstream. Indeed any thoughts that RCD provision at/before the wall socket could be omitted because what's normally plugged into them incorporates its own RCDs is going about things the wrong way. Likewise where a pre-existing socket doesn't have RCD protection, the correct solution would be to add RCD protection at or before the socket, not after it.

   - Andy.

But plug-in RCDs aren't covered by BS7671.  So just because BS7671 has suddenly declared that type A RCDs don't work, it doesn't mean that they don't work when plugged into a socket.

 I suspect many folk work in buildings that predate designs for RCDs everywhere, and will continue to do so for many years. I know I do.
 Perhaps sockets outdoors will be covered, but not all by any means. In such places, higher risk kit that may be taken anywhere, including to client sites of unknown condition, and work benches where equipment may be worked on open frame to repair it, may well be prudently fitted with an RCD plug as a means to reduce risk somewhat relative to not bothering at all.
The absence of RCDs in the building wiring is only a C3 at last inspection, and will wait until major works means the buildings are rewired or rebuilt. The comment level may change from C3  to C2 on some future inspection of course, but that decision may well not be made until some point in the 2030s.
I'd not be brave enough to say it was wise to remove all RCD plugs just yet,  and say these are never needed, in my mind they should stay except if one actually causes a problem.
Mike.

Simon Barker said:

But plug-in RCDs aren't covered by BS7671.  So just because BS7671 has suddenly declared that type A RCDs don't work, it doesn't mean that they don't work when plugged into a socket.

But it does (or could be claimed to) represent "state of the art" thinking regards risk assessment in this respect?

Plug-in RCDs certainly useful when talking 'power of opportunity' from other people's sites no argument there - but I can easily imagine (given what my local H&S mob are like) the 'elves' taking the attitude that for their own site, that if RCD protection is found to be missing then they want the problem fixed properly (by RCDing the socket or before) rather than relying on a plug-in solution that risks be trivially or accidentally defeated.

You know the kind of scenario they come up with - your people knew RCD protection was missing from the socket, but chose not to do do anything about it because what was usually plugged into it had an RCD plug. Months later someone then unplug it and plugs in something else (perhaps a direct replacement of the original equipment, factory fitted with an ordinary plug), something goes faulty, someone gets hurt, HSE start asking if you did everything reasonable to avoid the danger...

It's not the plug-in RCDs themselves that's the concern, but that they would be used as an excuse to sweep a problem under the carpet as it were.

   - Andy.