RCD sockets in the Garage? Or Plug in RCD?

[EFLImpudence]

Yes, I have.
Do they not state this in the literature?

Trying to work out how the removing CPC is recognised.
Is a resistance to the CPC used as part of one, or both, of the coil sensors
Edit - not both.

Does that mean it uses a little (however little) current all the time?

 

[333rocky333]

Hmmm - I don't think that does make a lot of sense - at least, not to me!

It would be very difficult (at least for me!) to think of any mechanism that could result in a 'poor earth' causing the RCD to trip.

Kind Regards, John

Thats what i was trying to explain earlier.
Im not sure its a design feature, maybe just the consequence of how the things internally wired.
I just found out by chance when one would not reset, i put a tester on the back and the earth showed up poor, after sorting that it worked.
As john found it seems relevant to Powerbreaker ones.

 

[John D v2.0]

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

sorry can't remember, and I'm not sure where it is now as I don't use it nowadays! If I find it I'll have another look inside though as it's a good question.

 

[JohnW2]

Thats what i was trying to explain earlier. Im not sure its a design feature, maybe just the consequence of how the things internally wired.

If it's not a deliberate 'design feature', there would seemingly be no reason for the CPC to be 'internally wired'to anything, unless it was being used for the test facility (which, as I said, you and I could not ascertain without looking inside - which would be a destructive exercise!)

... As john found .....

That's me!- who did you think you were replying to?

Kind Regards, John

 

[JohnW2]

Trying to work out how the removing CPC is recognised.

That's what we don't really understand.

Is a resistance to the CPC used as part of one, or both, of the coil sensors Edit - not both.

I can't really think of how it could be.

Does that mean it uses a little (however little) current all the time?

Particularly given that it presumably has to detect not only that a connection to earth is present, but also that the impedance of that connection is below some figure, it seems pretty inescapable (at least, to me) that a least some current (as you imply, possibly very little) must flow through that earth connection all the time.

Kind Regards, John

 

[EFLImpudence]

Do you know how active ones switch off on loss of power?

It could be the same sort of device for unconnected CPC.

 

[JohnW2]

Do you know how active ones switch off on loss of power?

No, but I would imagine that it's just a simple 'latching' arrangement (implemented either electronically or electro-mechanically) - i.e. pressing the Reset button momentarily turns the device on, but, once power appears at the output, that sustains the 'on state' so long as there is still power. If the power supply fails, that 'sustaining' then stops, and the device remains 'off' unless/until the Reset button is pressed (with power available).

It could be the same sort of device for unconnected CPC.

I can't really think of any sensible equivalent for the CPC. I suppose that they could use the L-CPC pd to do the sustaining I just mentioned, but that would be very odd, and would mean that (as per your previous comment) that the device would probably be generating some earth current all the time it was being used.

The behaviour of the (passive) Powerbreaker one I tested yesterday was interesting. Without an earth, it switched itself off. If (with no earth) one pressed the Reset button, nothing happened, but when one released the Reset button, the device switched 'on' for a fraction of a section (long enough for an incandescent lamp/bulb load to light up). I'm not sure what that means!!

Kind Regards, John

 

[333rocky333]

That's me!- who did you think you were replying to?

Kind Regards, John

I was replying to Efl
He was also strugling to see how no earth tripped the rcd, thats why i quoted your bit, as it seemed you could not explain it either

 

[EFLImpudence]

Tis magic.

 

[333rocky333]

I noticed today on the packaging for the passive ones it Says Mechanical Latching, no need to reset after power loss.
Next time i get a dodgy one I will open it up

 

[JohnW2]

I noticed today on the packaging for the passive ones it Says Mechanical Latching, no need to reset after power loss.

Well, yes, I suppose that's just a 'statement of the obvious' about what 'passive' means. As I said, in an 'active' one the 'latching' must be done electrically - as with a relay.

Next time i get a dodgy one I will open it up

I don't think you would learn anything we don't already know by opening up a passive one - we all have a fairly clear idea of how those work, and many of us have opened up a good few.

What we really need to look inside is one of these Powerbreaker ones, since that is where the real uncertainty/'mystery' is - since they are 'passive' RCD which will only stay 'latched' with an earth connection (so, unlike what you're looking at, clearly not just 'mechanical latching' - even though they do remain 'latched' on loss of {L & N} power!).

Kind Regards, John

 

[ericmark]

Sorry Eric. That is not the case. You cannot discriminate RCDs by using CURRENT (like you do with MCBs). You must have TIME as the discrimination factor.

Think about it. Lets say you have a string of RCDs 100mA at the source, 30mA in the middle and a 10mA at the load end.
Granted that a small earth fault on the load end of say 20mA will take out the 10mA, and not the others, BUT this rarely happens,
What you usually get is a socking great big earth fault!

In that case probably all three RCDs will trip, maybe just the one that goes is the one with the quickest trip time, could be any one of them.

That's why we use a time-delay type S RCD, typically at the source of TT installations.

Not read the rest, but had an alert on this. Yes with a full blown short line to earth all RCD's will trip, I remember a nail to hang a coat up in a portacabin at Sizewell "B" building causing a line to earth fault. The 30 mA at 40 mS when out, so did the 100 mA at 1 second in local board, so did the 0.5 amp at 1 minute in our main board, and the 1 amp at 5 minute in the main contractors board. It does not matter what time or what time delay with a short circuit they all trip.

However in the main a RCD will trip because something is starting to fail, water or dampness is a major cause, and the leakage slowly builds up to a point when the device will trip. In this case the 30 mA will go before the 100 mA and time does not really matter. I am talking about earth leakage rather than a full blown short circuit. So with a 10 mA RCD feeding the pond, when water or dampness enters the junction box over a time a carbon track builds up and then the 10 mA will trip before the 30 mA in the house.