RCD sockets in the Garage? Or Plug in RCD?

[JohnW2]

Usually powerbreaker, I may be able too try one during the week

No need to wait - my experiment 2 is now done.

You're right about the Powerbreaker. I've just tried with a Powerbreaker H22. As you say, it won't reset without an earth connection. Furthermore, if one disconnects the earth whilst it is 'on', it immediately trips. It's therefore impossible to ascertain whether or not the test button is 'testing to earth' but, for what it's worth, when one does have an earth connection, the test button works as expected, and does not take out the upstream (also 30mA) RCD.

Kind Regards, John

 

[333rocky333]

Well done john, thats what I thought I had encounterd.
Thinking back the ones I encountered that took out the upstream Rcd were not powerbreakers, they were stainless steel finish

 

[333rocky333]

. It's therefore impossible to ascertain whether or not the test button is 'testing to earth'

Not like you to say "Impossible"

 

[John D v2.0]

In case it adds to the debate, my plug in active one does the test by passing a current through a third wire that goes through the core. So it's not testing a real fault, just creating an apparent imbalance.

 

[JohnW2]

Not like you to say "Impossible"

Well, virtually impossible (and literally impossible for you an I!) by testing - since the moment one disconnects the earth, the device trips, before one even has a chance to press the test button.

I suppose that, given appropriate fancy testing kit, one could ascertain whether there were a handful of mS of (low) current in the CPC when one pressed the test button but, for us mere mortals, the only way of finding out would be to take one apart and see what the test button is connected to!

Kind Regards, John

 

[JohnW2]

In case it adds to the debate, my plug in active one does the test by passing a current through a third wire that goes through the core. So it's not testing a real fault, just creating an apparent imbalance.

I suppose that's fair enough, even though not testing exactly what happens when the device is meant to operate in-service. Do you know how that current through the third wire is derived - from L & N or L & E ??

Kind Regards, John

 

[JohnW2]

Well done john, thats what I thought I had encounterd. Thinking back the ones I encountered that took out the upstream Rcd were not powerbreakers, they were stainless steel finish

One would imagine that if the test button creates a current to earth, there is always going to be the risk/possibility that any upstream RCDs with the same (or lower) IΔn will trip - although there would probably be no guarantee that it/they would trip.

Indeed, I suppose there is the possibility that the upstream one will trip but not the one which is being tested, even if the one being tested is actually 'in spec'. Albeit erring on the side of caution, that might be one potential downside of 'testing to earth' when an upstream RCD is present.

Kind Regards, John

 

[333rocky333]

I suppose that, given appropriate fancy testing kit, one could ascertain whether there were a handful of mS of (low) current in the CPC when one pressed the test button but

That was what i thought too

So in the OPS case and for others, then it could warrant an ACTIVE RCD for the safety aspect, even though theres an upfront Passive Rcd or Rcbo in the board.
But the active Rcd either plug in or fixed socket used, would be dependant on how the test facility is wired

 

[JohnW2]

That was what i thought too

Indeed, but outside of specialised labs, I doubt that many people have gear that can detect an AC current of a handful of mA flowing for just a handful of mS - so, as I said, essentially 'impossible' for mere mortals like us!

So in the OPS case and for others, then it could warrant an ACTIVE RCD for the safety aspect, even though theres an upfront Passive Rcd or Rcbo in the board.

Well, there's certainly an argument for having some sort of NVR switch if there is a risk of equipment springing dangerously back to life after a power cut, but (redundancy aside) it doesn't necessarily have to have any RCD functionality.

Kind Regards, John

 

[333rocky333]

It may be just because of my limited experience, but I don't think I'm come across (certainly not recently) an RCD socket or adaptor (and probably also RCD FCUs) which was not 'active'.

Kind Regards, John

A quick google suprisingly, apart from plug in types, seems more are passive.
Screwfix sockets and FCUs all seem passive apart from 1 active mk socket

http://www.screwfix.com/c/electrica...tm_content=Switches and Sockets - RCDs - Bulk

 

[dishman]

Well....I cannot say I understood all of that...I enjoyed the discussion though.

But for what it is worth, I have been using a plug in RCD (just out of habit). I do use the test button each time I use it and it has never tripped the RCD on the consumer unit. As it is a plug in variety, it does act as an active RCD as it trips if power is disconnected.

However, you have to trust that the RCD will do it's job and really does work if and when required.

 

[JohnW2]

A quick google suprisingly, apart from plug in types, seems more are passive.
Screwfix sockets and FCUs all seem passive apart from 1 active mk socket

It surprised me, too. All I can say is that my experiences this afternoon are consistent with what you say - the MK one was (and said it was) active, whereas the Powerbreaker one was passive. The latter was, of course, a little more complicated, in that it did not trip in response to loss of L and/orN, but it did trip if one removed the earth connection whilst it was receiving power!

Lest anyone reading this discussion might be getting confused, it's probably worth pointing out that the issue of whether an RCD is active or passive is totally separate from the question of whether it's test button introduces an L-N or L-E current. One can, at least in theory have an active RCD which uses either test method, or a passive one which uses either test method.

If my suggestion that the 'L-E test button' approach is in order to detect the absence of an earth connection is correct, then whether it is active or passive is probably irrelevant - what really matters is whether or not it is a 'peripheral' device (e.g. a socket or plug-in) 'at the end of a circuit' (which may or may not have an effective CPC).

Kind Regards, John

 

[JohnW2]

I do use the test button each time I use it and it has never tripped the RCD on the consumer unit. As it is a plug in variety, it does act as an active RCD as it trips if power is disconnected.

Fair enough but note that, as I've just written to Rocky, an active RCD (just as is true of a passive one) can use either of the test methods (introducing a 'leak' to neutral or to earth), but only the latter of those two approaches carries any risk (and no guarantee) that pressing the button will cause an upstream RCD to trip.

Kind Regards, John

 

[333rocky333]

Is it just me, or have we learnt something today

 

[JohnW2]

Is it just me, or have we learnt something today

I certainly have leant a couple of things - firstly that there are at least some RCD units around (like the Powerbreaker one) which will immediately trip if their earth connection is removed (and won't reset unless/until the earth connection is restored) and, secondly, that passive RCD sockets/adapters are probably more common that I thought was the case.

Kind Regards, John