Bathroom notifiability

[John D v2.0]

No it would not.

Oh yes it would!

Oh forgot it's not the panto - go on explain!

Not sure if it's possible to make an RCD that's powered entirely off the current difference from the coil, but I agree that fundamentally there's nothing in the concept of an RCD that needs a voltage difference. You could have 20 conductors with millivolts between them all, and still trip on an arbitrary imbalance. Make it battery powered perhaps.

 

[ban-all-sheds]

With a separated ELV supply, how do you get an imbalance?

 

[JohnW2]

No it would not.

Why not?

As I've recently reported (post #3), even with electronics, it appears that a bog-standard RCD works down to at least 6V, perhaps appreciably lower (watch this space!), although I presume that there has to be a lower limit.

However, in the absence of any electronics to power, I see no reason why there has to be any lower limit at all. If a 30mA imbalance current is enough to trigger the trip mechanism, then it will do so regardless of what PD exists between the L and N terminals of the RCD.

That all seems so obvious that I would expect you to know and agree with it - so I have to wonder whether you have thought of some subtle issue, maybe about my use of words, at which you can nit-pick.

Kind Regards, John

 

[JohnW2]

With a separated ELV supply, how do you get an imbalance?

I was talking in general ("For a start...") about non-electronic RCDs not knowing or caring about voltage ... and I did go on to say that there was, in any event, no point in trying to RCD protect an ELV (which I was using to mean 'isolated') circuit.

.. so its seems that it probably was 'nit-picking'.

Kind Regards, John

 

[ban-all-sheds]

With a separated ELV supply, how do you get an imbalance?

 

[ban-all-sheds]

You were talking "in general" in a reply to a post about SELV supplies?

And yes, you did go on to say there was no point, but that was after you said it would work with a non-electronic RCD.

 

[JohnW2]

Oh forgot it's not the panto - go on explain!

It appears that he was trying to be 'clever' by pretending he didn't understand the context and scope of my statement.

Not sure if it's possible to make an RCD that's powered entirely off the current difference from the coil, but I agree that fundamentally there's nothing in the concept of an RCD that needs a voltage difference. You could have 20 conductors with millivolts between them all, and still trip on an arbitrary imbalance. Make it battery powered perhaps.

Indeed. I would doubt that it would be possible to power electronics from the 'difference coil'. Apart from anything else, that difference could well be zero, or very nearly zero, except when the device was required to operate, so the electronics would be without power for most of the time, and would have to 'spring to life' in the event of being needed - which probably would be pushing things if one were to achieve the required operation times. More realistic might be to have a second coil around just one conductor, so the electronics could be powered by the actual current flowing (rather than the current imbalance) - but, again, there would presumably be some lower limit to even that. Battery powered obviously would work, but would bring some obvious problems and concerns.

However, there does not have to be any electronics at all (early RCDs did not have any), in which caser voltage becomes totally irrelevant.

Kind Regards, John

 

[JohnW2]

With a separated ELV supply, how do you get an imbalance?

For goodness sake, how many times do I have to say that I wasn't suggesting that one can? You're just nit-picking for the sake of it.

Kind Regards, John

 

[JohnW2]

You were talking "in general" in a reply to a post about SELV supplies? And yes, you did go on to say there was no point, but that was after you said it would work with a non-electronic RCD.

As I suspected, you're just playing games. It really is a pain having to try to check and re-check everything I write in an attempt to make sure that there is not some imperfection in my wording which you (but no-one else) can make an issue out of.

I suppose, with just you in mind, I probably should have started my sentence with "Even if an SELV could result in a current imbalance, .......". If it makes you any happier for me to admit that, please feel free to feel that you have "won".

Kind Regards, John

 

[ban-all-sheds]

With a separated ELV supply, how do you get an imbalance?

For goodness sake, how many times do I have to say that I wasn't suggesting that one can?

That was posted in reply to this:

Why not?

As I've recently reported (post #3), even with electronics, it appears that a bog-standard RCD works down to at least 6V, perhaps appreciably lower (watch this space!), although I presume that there has to be a lower limit.

However, in the absence of any electronics to power, I see no reason why there has to be any lower limit at all. If a 30mA imbalance current is enough to trigger the trip mechanism, then it will do so regardless of what PD exists between the L and N terminals of the RCD.

That all seems so obvious that I would expect you to know and agree with it - so I have to wonder whether you have thought of some subtle issue, maybe about my use of words, at which you can nit-pick.

Kind Regards, John

Not the one it actually followed, and in which you were still missing the point, and thinking that it was the E that might be a problem, not the S.

Nothing to do with "winning" - you kept on saying the same thing about the magnitude of the voltage, so I kept on asking the same question.

 

[JohnW2]

Nothing to do with "winning" - you kept on saying the same thing about the magnitude of the voltage, so I kept on asking the same question.

If it's not about "winning", why on earth are you continuing to go on about it?

Even if it was not initially apparent because of the words and/or structure of my initial comment, and/or the material I quoted, I have surely subsequently made it clear that I agree that (unless one is rather silly**) a 2-wire 'floating' supply (such as SELV) cannot develop a current imbalance in those two wires - such that there would clearly be no point in trying to 'RCD protect' it.

Given that I have made it clear (to all) that I agree with that, I am at a loss to understand what you could be hoping to achieve by continuing to labour the point, if not some strange attempt to 'chalk up some sort of marks for yourself'. Your posts seem to imply that you are expecting some new response from me, but I'm not clear what more/new you would like me to say.

[ ** since there seems to be more than a degree of pedanticism afoot, I'm not at all sure that, provided the SELV supply remains 'separated' from earth, there is anything which prohibits a network of 'CPCs' originating from one side of the origin of an SELV supply, and for those CPCs to be connected to exposed-c-ps (and maybe also some internal conductive parts) within the SELV circuitry. If that is allowed, then it would mean that a fault between 'the other side' of the SELV supply and an exposed-c-p would result in a current imbalance in the 'final circuit' involved, which could be detected and acted upon by an RCD. I think one might struggle to think of a reason why anyone would want to do that, but that's a different matter ]

Kind Regards, John

 

[ericmark]

I'm just 'done the (preliminary) experiment' and, even with electronics, they are even less concerned about voltage than I suspected ...

... a bog-standard (brand new) Wylex 80A 30mA RCD trips with ~30mA imbalance all the way down to a supply voltage of 6V. I haven't yet tried lower voltages than that, nor have I looked at the actual trip thresholds and (if my meter will do it) trip times at low voltages - but I will look at those things in due course.

Kind Regards, John

That is very interesting, I was lead to understand the whole idea of the active RCD was that if the fault reduced the voltage to a point where the RCD will not trip, then it trips anyway due to low voltage? At the consumer unit it is unlikely one could ever have a fault which could drop the voltage to a value where the RCD would fail but the fuse not rupture, however with a socket outlet there was I was told a chance a fault could cause enough of a volt drop to cause the RCD not to trip with a passive type.

However your tests seem to show that is not the case, and the RCD will trip? My understanding was under 50 volt no RCD was required, and I had raised the question with 55 volt to earth would a standard RCD work? The reason for the question is with yellow brick transformers with a 10A thermal trip on the incomer a phase to earth fault can draw over 40 amps without tripping the overload, which could cause the cable to melt. Having a RCD on a 63 or 55 volt to earth supply (depending if single or three phase) would be a great safety feature to prevent fire. But at over £50 for the in-line 110 volt RCD very expensive, nearly as much as the transformer. But 13A plug in type around £10 I am sure those for Europe are 16A?

However as to bathrooms and UK supplies, I would always use a RCD on any 230 volt supply to a bathroom, in fact to any 230 volt supply in the house, I have had 30 mA RCD's now for over 25 years in my house, but with a SELV supply even if one leg did go to earth it would not trip a RCD on the supply side of the transformer. The bathroom is now likely the only place in a new UK house which does not have RCD protection on the sockets. The shaver socket in the bathroom is likely the only socket in the house without RCD protection, however it does have a current limit 40VA so around 180 mA.

 

[John D v2.0]

To be honest I have trouble getting that worked up about any ban all sheds interpretations of the world, but delving back into the mists of time it seems pretty clear that ban all sheds selective quoting ericmark after the whole point was addressed, in order to make johnw2 look bad (although most people would assume it's just bas bring an arsenal hole so as I say, hard to get worked up)

How can any SELV be RCD protected? I have never seen a RCD that will work with 12 volt, and even at 230 volt with an IT supply a RCD is not really going to work.

For a start, an RCD without electronics would know nothing about voltage, and so would work as well with a L-N PD of 1V as with 230V

However, that's not the point.

Then later ban went back and made a new history using other people's words

How can any SELV be RCD protected?

For a start, an RCD without electronics would know nothing about voltage, and so would work as well with a L-N PD of 1V as with 230V

 

[ban-all-sheds]

If it's not about "winning", why on earth are you continuing to go on about it?

If it's not about "losing", why on earth are you continuing to go on about it?

 

[JohnW2]

That is very interesting, I was lead to understand the whole idea of the active RCD was that if the fault reduced the voltage to a point where the RCD will not trip, then it trips anyway due to low voltage?

Active RCD sockets/plugs/adapters certainly trip if the supply voltage falls below some value (I don't know what voltage, but will investigate if/when I have time), but one can only speculate about the reason behind this. As you say, my experiments suggest that it's not for the reason you thought. My assumption has always been that it was to achieve the 'NVR' functionality, particularly given that RCD sockets (and plugs, and adapters) were initially (any maybe still) often used to supply garden electrical tools which were being used remotely from the CU.

However your tests seem to show that is not the case, and the RCD will trip?

Indeed. Any passive RCD (such as the one I tested) will obviously 'hold in' (stay 'on') with any supply voltage (including zero) - but, yes, with a 6V supply it tripped immediately with a ~30mA imbalance. For no real reason other than curiosity, I'll be interested to see how low a voltage will still enable tripping, but I'm probably going to have to do some improvisation to get a 50Hz supply lower than 6V. Watch this space.

My understanding was under 50 volt no RCD was required ...

There seems to be a common assumption that 50V is 'safe', but given that body resistance of 1 kΩ or less is far from impossible, the resultant ≥50mA current could certainly be lethal in some cases.

However as to bathrooms and UK supplies, I would always use a RCD on any 230 volt supply to a bathroom ...

That, of course, is what BS 7671 now requires, and what we've been discussing in this thread.

... in fact to any 230 volt supply in the house

Again, in terms of sockets, that's what BS 7671 now requires (and, as of next year, probably with NO exceptions).

... The shaver socket in the bathroom is likely the only socket in the house without RCD protection, however it does have a current limit 40VA so around 180 mA.

Yes, but that will be SELV, so as you have said (and BAS has laboured), RCD protection of that would achieve nothing.

Kind Regards, John