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

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.

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.

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.

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.

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?