Global IR testing on RCBO populated CU

[Midwest]

I shall be replacing my dual RCD CU, for a all RCBO populated CU. A question or two about technique for IR testing.

For the IR test, I've read here before that a global IR test is preferable. With older types of RCBO's that wasn't possible, without disconnecting cables, which ended up with the testing of each individual circuit.

I'm installing a Hager CU, with their miniature ADA RCBO. The MI state an IR test can be carried out on the RCBO terminals, circuit connected with the RCBO turned off. As I've a few different sorts of luminaire connected, I will be doing live/neutral to to earth.

How do you carry out such a test? I've seen some stackable MFT leads, so you can combine live & neutral together?

 

[pc1966]

I think ROI is mostly TN-C-S now so no need for an incoming RCD. In any case there has to be some form of over-current protection so it would need to be an RCBO here.

 

[Mike Johnson]

I think ROI is mostly TN-C-S now so no need for an incoming RCD. In any case there has to be some form of over-current protection so it would need to be an RCBO here.

Of Course, but I do believe that the majority of rural ROI properties are still TT, but I have no facts to back that up except for the lodge I stay at in Enniskillen.

 

[nicebutdim]

Of Course, but I do believe that the majority of rural ROI properties are still TT, but I have no facts to back that up except for the lodge I stay at in Enniskillen.

Enniskillen is in NI.

 

[pc1966]

I think rural is often TT (or to all intents and purposes, TT) in most of the world, as you don't easily get a low R earth and you might want to avoid the transformer's LV one as it may be too close to any HV side earth.

 

[LastManOnline]

That is interesting. Certainly makes it easier to disconnect the CU supply to do any work!

It is just a regular MCB (not MCCB)?

Yes.The difference between it and the other mcb, s is that it may be a "C" instead of a"B" type if the supply characterises allow. You raise an interesting question in my mind though as to why it can be a regular MCB instead of an MCCB and offhand I suspect it may have to do with the DSO, s protective fuse in the meter cabinet. Must look into that.
Regarding the DP main switch, well that is simply a gift for a number of reasons but chiefly we can now do IR tests effortlessly on non - rcd protected circuits on TNC-S systems without having to first disconnect the main Neutralising earth from the bus-bar.

 

[pc1966]

Ah, I think we have some misunderstanding here!

You seem to be talking about having a DP MCB as the main CU supply switch, where as I was thinking of the DSO/DNO supply fuse being replaced by a MCB which troubled me a bit.

This makes a bit more sense, as the DSO fuse would provide the ultimate back-up for a major fault and the MCB is then a combined switch and current limit that comes in below the fuse and saves the DSO trouble if someone overloads the CU total capacity.

We have always had DP incoming switches for the CU and as you say it is so sensible that you can isolate the lot to do a global IR test without having to remove cables and risk further faults being introduced.

 

[Mike Johnson]

Enniskillen is in NI.

I know, but I am a cross boarder fisherman. ?

 

[pc1966]

...on TNC-S systems without having to first disconnect the main Neutralising earth from the bus-bar.

That is something we don't have in the UK but I suspect the ROI system is more like the USA where the E & N are linked in the "installation" side and not in the "supply side"?

They also have a requirement for local earth rods as well as the supply's combined N & E cable.

In UK only the DSO/DNO links E & N and for the TN-C-S case that is at the cut-out (main supply fuse) that provides the power feed to the billing meter and from there to the installation.

 

[LastManOnline]

Of Course, but I do believe that the majority of rural ROI properties are still TT, but I have no facts to back that up except for the lodge I stay at in Enniskillen.

Yes. That is so in N. I. In ROI we are going full TNC-S

 

[LastManOnline]

Is this on the supply side or is Ireland moving away from fused plugs on domestic appliances?

No. There are no moves afoot to move away from fused plug tops here. Ironically this is where you find the UK influence in ROI. There are very, very few countries in the world with fused plug tops. They are a direct consequence of the 32 amp ring final circuit. In practice we in the ROI could easily eliminate the fused plug top arrangement but the hassle just is, nt worth it. And while I am not a big fan of ring circuits I recoqnize they have their uses

 

[Simon47]

Ah yes, the "project" to get rid of fused plugs. I forget how many decades it is now that I've been reading about how the whole of the EU (or perhaps Europe as the geographic area) is going to have one standardised plug - which will be unfused because it's only us silly buggers in the UK (and it seems Ireland) use them. And of course, much discussion on how to adapt UK wiring (split rings into two radials) without having to go "full rewire".
I guess that eventually fizzled out when it became clear that everyone was "in favour as long as you pick my system".
Mind you, how long did it take before round pin plugs became the "rare exception" after we invented the "13A" plug.

 

[pc1966]

At one point the IEC "kettle" connector looked promising as used everywhere, but the biggest issue is the old chicken & egg issue: Why change?

There is a huge investment in every country in both infrastructure and appliances, so what is the benefit either economically or safety for such a change. Some countries, like Italy, still have two standards in use on a broadly north/south split as its just not worth changing stuff.

As you pointed out, the UK had round pin stuff in common use until the 70s or later, and even then when the 13A plugs were introduced it was just after WW2 and hardly any domestic electrical stuff in use by today's standards.

So no matter how much one argues for/against fused plugs, or the RFC/radial, it makes little difference in the real world as folk will keep with what is in use and works. We have fused plugs, hence the 32A RFC is a good idea. Other places don't, so 16A (or so) radials are a good idea.

 

[Simon47]

This wasn't a fused vs unfused issue - it was a "lets have just ONE standard across the whole of Europe". Do you know how many standards there are across Europe ? You've mentioned Italy having two - I know they have two sizes (like we used to have 5A and 15A). Contrary to what many believe, France and Germany don't share plugs/sockets - their standards are different.
And for good measure, there's one combination of plug and socket (French* plug in German socket) which mate and appear to work fine - but doesn't connect the earth ?
* That's the French plug, not the common hybrid that has both the French and German earthing contacts.

Anyway, it must be over 4 decades ago I was reading about this great idea to create one standard across the whole of Europe - unfused because so many countries see our fused plugs as somehow "wrong", and incompatible with any existing system so as to avoid the "we're not adopting <some country>'s system" problem. I guess, for the reasons already given, the idea eventually fizzled out.

 

[nicebutdim]

The Europlug fits most sockets across mainland Europe, which is a reasonable achievement.

As best I can remember there is also an issue with German Schuko plugs fitting in some sockets (other countries) that they shouldn't be used with.

 

[LastManOnline]

This wasn't a fused vs unfused issue - it was a "lets have just ONE standard across the whole of Europe". Do you know how many standards there are across Europe ? You've mentioned Italy having two - I know they have two sizes (like we used to have 5A and 15A). Contrary to what many believe, France and Germany don't share plugs/sockets - their standards are different.
And for good measure, there's one combination of plug and socket (French* plug in German socket) which mate and appear to work fine - but doesn't connect the earth ?
* That's the French plug, not the common hybrid that has both the French and German earthing contacts.

Anyway, it must be over 4 decades ago I was reading about this great idea to create one standard across the whole of Europe - unfused because so many countries see our fused plugs as somehow "wrong", and incompatible with any existing system so as to avoid the "we're not adopting <some country>'s system" problem. I guess, for the reasons already given, the idea eventually fizzled out.

I don, t believe others see your plugs as "wrong", the europeans just see their plugs as better because they don't have the hassle of needing to change fuses. I agree with "them" on this point.
However as you correctly point out there are aspects to "their" plug tops which are inferior to the UK. They are often unearthed, flimsy and can be reversed plugged in meaning correct polarity can't be assured. I agree with "you" on these points.