RCD sockets in the Garage? Or Plug in RCD?

[John D v2.0]

John that's interesting, I think there are two benefits of an RCD for equipment outside. One is as you say for class 1 equipment, for example if it gets wet or there's an l/e fault at the far end of a long extension lead. The other I see it as running over the cable with the mower or chopping with the hedge trimmer.
I think out of all the things people do, garden maintenance is probably the most popular thing where people might damage the cable.

 

[JohnW2]

John that's interesting, I think there are two benefits of an RCD for equipment outside. One is as you say for class 1 equipment ...

Sure - but, as I said, I think that Class I 'outdoor equipment' is becoming (or has already become) pretty uncommon.

The other I see it as running over the cable with the mower or chopping with the hedge trimmer.

I mentioned that as well and admit that I have chopped the cable with a hedge trimmer more than once! However, as I said, the equipment is usually Class I and the cable hence very commonly 2-core - which means that an RCD would be of no use, other than in the one (pretty unlikely) scenario I mentioned (it's certainly the case that every time I've chopped a hedge trimmer cable, an OPD {fuse in plug and/or MCB} has operated).

Kind Regards, John

 

[333rocky333]

Depending on what your using in the garage, then the disadvantage of using the Rcd in the board is that they are passive Rcds, whereas a plug in device, possibly what the NICEIC are getting at, and Rcd sockets are active.

In the rare event of a power cut, you would not want a mower blade to start while fiddling with it, so a 2nd active unit could be an advantage.
Though as said, the 1st Test button often trips the 2nd unit, maybe theres a small demand for units that dont Test to Earth

 

[JohnW2]

Depending on what your using in the garage, then the disadvantage of using the Rcd in the board is that they are passive Rcds, whereas a plug in device, possibly what the NICEIC are getting at, and Rcd sockets are active.

Maybe that's their thinking but, if so, they are presumably being far from clear - since it is not the RCD functionality, per se, that they are talking about.

Though as said, the 1st Test button often trips the 2nd unit, maybe theres a small demand for units that dont Test to Earth

As always, I may be wrong, but I've always suspected that the reason why these 'peripheral' RCDs all seem to 'test to earth' is that, by so doing, they are confirming the presence of an effective earth connection at the socket/adapter/whatever, as well as testing the RCD's functionality.

Kind Regards, John

 

[333rocky333]

As always, I may be wrong, but I've always suspected that the reason why these 'peripheral' RCDs all seem to 'test to earth' is that, by so doing, they are confirming the presence of an effective earth connection at the socket/adapter/whatever, as well as testing the RCD's functionality.

Kind Regards, John

I have noted though rcd sockets, if they have a poor earth they trip off, even without operating the test button, unles that derives from the electronics used, for the actual way the test button works, if that makes sense

 

[JohnW2]

I have noted though rcd sockets, if they have a poor earth they trip off, even without operating the test button, unles that derives from the electronics used, for the actual way the test button works, if that makes sense

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

If the test button introduces a 'leak' from L to the available 'earth' (i.e. the local CPC), the RCD will obviously not trip if that earth is too 'poor' (too high impedance). 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

 

[securespark]

But wouldn't it have to be exceedingly high, ie >1666Ω for it not to trip?

 

[winston1]

If the test button introduces a 'leak' from L to the available 'earth' (i.e. the local CPC), the RCD will obviously not trip if that earth is too 'poor' (too high impedance). 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

If the L and N are reversed at the socket it won't trip either. Could be another reason for using this method.

 

[JohnW2]

But wouldn't it have to be exceedingly high, ie >1666Ω for it not to trip?

Actually, 7,666Ω (total loop impedance).

However, I would think that the most likely problem at a socket would be for its CPC not to have any continuity with earth at all. In that situation, an 'L-E test button' would not result in a trip (thereby alerting one to the existence of 'some problem'), whereas an 'L-N test button' would result in a trip (leaving one oblivious to the problem).

Kind Regards, John

 

[JohnW2]

If the L and N are reversed at the socket it won't trip either. Could be another reason for using this method.

Indeed. Just as with the 'absent earth connection', an L-N reversal would result in the test button not causing a trip. In both cases, it would alert the user to the existence of 'some problem', albeit (which they probably would not realise) not a problem with the RCD.

Kind Regards, John

 

[333rocky333]

im pretty sure from memory that with NO earth the sockets will not turn on, I recall at least 1 that would not reset on, and when supply was checked there was no earth and when it was reinstated it worked.

 

[JohnW2]

im pretty sure from memory that with NO earth the sockets will not turn on, I recall at least 1 that would not reset on, and when supply was checked there was no earth and when it was reinstated it worked.

I can't say that I have personally experienced that, but that could be simply due to the fact that I have never encountered such a device that had no earth connection.

If what you say is true, then I think it would have to be due to be deliberately-engineered additional functionality, since it would be easy enough to produce an active RCD which didn't care whether or not it had an earth connection.

I think I need to do some experimentation - watch this space

Kind Regards, John

 

[JohnW2]

I think I need to do some experimentation - watch this space

Hmmm - first experiment done, but it hasn't provided all the answers ...

An MK Sentry 56231 30mA active RCD socket will reset happily with no earth connection. However, the test button also works 'as expected' with no earth connection - so MK obviously don't feel it necessary and/or appropriate to use the 'test to earth' approach for this particular active RCD.

I need to try to find one of a different make. Perhaps ones with 'test to earth' are less common than I thought!

Kind Regards, John

 

[333rocky333]

Are the ones that stay on Passive, those I encounter are in pub cellers so Its likely they would have been Passive rather than active

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

 

[JohnW2]

Are the ones that stay on Passive, ...

After a power cut? Yes, the ones which stay on in that situation are passive.

those I encounter are in pub cellers so Its likely they would have been Passive rather than active

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