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?

 

[nicebutdim]

That shows the trip part as the 'X' crossing the live path just after the switch symbol.

I think it is often seen that a MCB/MCCB is shown just as an X on power schematics.

What are the practical differences between the two schematics? I don't fully understand either, but this is a great alternative to painting the kitchen.

 

[Mike Johnson]

No ----- on this image:

 

[pc1966]

What are the practical differences between the two schematics? I don't fully understand either, but this is a great alternative to painting the kitchen.

I think it is just one of conventions.

Originally schematic parts would show things representative and easy for humans to draw, like coils for inductance. Then CAD and pen-plotters came along and they were simplified to boxes to make it ease for machines to draw.

 

[pc1966]

No ----- on this image:

So RCCB really means "residual current, concealed -----"?

 

[LastManOnline]

Is a neutral busbar worth the additional space required for 2 module RCBOs?

That is a fair point.Often the space is, nt available in older installations. In newer installs space is generally a non-issue. But I can assure from experience that once you install a CU with dual module rcbo, s you will find yourself seeking to "make the space" on your next install. I find installation time is nearly halved. Its a bit like comparing a WAGO push in to a traditional connector. They are also very convenient for testing and for faultfinding.

 

[nicebutdim]

That is a fair point.Often the space is, nt available in older installations. In newer installs space is generally a non-issue. But I can assure from experience that once you install a CU with dual module rcbo, s you will find yourself seeking to "make the space" on your next install. I find installation time is nearly halved. Its a bit like comparing a WAGO push in to a traditional connector. They are also very convenient for testing and for faultfinding.

I don't doubt the benefits, but was thinking more from a customer perspective in domestic settings and exterior space used as opposed to interior space available.

 

[LastManOnline]

I don't doubt the benefits, but was thinking more from a customer perspective in domestic settings and exterior space used as opposed to interior space available.

Again a valid point. But nowadays (down here at least), CU, s tend to be located in utility areas rather than hallways. CU, s are also much more presentable than they used to be and with cover attached fade into the background. And realistically, how much extra space are we talking about? The new GE CU is basically an enlarged 2 row CU. They added 2" to the the width and approx 4" to the length. More than adequate for a complete rcbo CU in a 3 bedroom house here. And that's allowing for the fact we use more circuits per domestic dwelling than the UK.

 

[nicebutdim]

Again a valid point. But nowadays (down here at least), CU, s tend to be located in utility areas rather than hallways. CU, s are also much more presentable than they used to be and with cover attached fade into the background. And realistically, how much extra space are we talking about? The new GE CU is basically an enlarged 2 row CU. They added 2" to the the width and approx 4" to the length. More than adequate for a complete rcbo CU in a 3 bedroom house here. And that's allowing for the fact we use more circuits per domestic dwelling than the UK.

My experience is exceptionally limited - so limited that it extends to a single installation, although it still allows me to see the logic in the points you make. For several practical reasons only a few circuits were replaced at a time and I delayed fitting the new CU for as long as possible, to allow as many cables to be dressed at one time as feasible as it was obvious that each additional circuit would become increasingly difficult to dress neatly. At the time I remember looking at images of 3 phase boards and wondering why we didn't use the likes in domestic settings.

That being the case, I'm still wondering what the benefits would have been of using 2 module RCBOs?

The installation in question is TT, with ZE of 16 Ohms. I don't have PFC or PSC to hand, but suffice to say they weren't sufficient to meet requirements for disconnection of MCBs. As such I opted for a Crabtree Starbreaker 1P+N RCBO board (why don't all manufacturers use plug in busbars?) and fitted a 100mA type S RCD upfront (will I burn in hell for fitting it in a plastic enclosure?).

Forgetting about availability etc; other than convenience for the installer, the question I've been trying to ask is what benefit would have been derived from using 2 module DP RCBOs? I was trying to make a dangerous situation better in circumstances that no one wanted to know about and, given that my parents live in that house, would have spared no expense in trying to make it as safe as possible.

Answers in simple terms please as you're not conversing with an expert.

 

[LastManOnline]

Answers in simple terms please as you're not conversing with an expert.

From an electrical safety point of view, I would have no concerns vi's, a vi's single module or double module rcbo, s. From an installation and maintenance (faultfinding) and testing point of view, (IR testing and neutral earth fault finding) I would suggest that dual module are a standout winner.
You rightly ask, "but is there any advantage in this for the consumer"? Unquestionably.
Firstly difference in cost between single and dual module is more than offset by labour cost benefits in time saved with installing dual module rcbo, s.
Secondly, faultfinding of any circuit is greatly helped by being able to isolate both poles. Having to trace out and disconnect the neutral from the busbar is not a task you want to have on your plate. In reality you never really want to be disconnecting neutrals and earth's from their respective busbar unless it's absolutely necessary.
Ironically, this morning I was called to a premises installed by our UK based partner (from N. I.) They installed single module rcbo, s as is the norm for UK. Whenever I see they, my instinctive reaction is "oh no! Whatever the problem is has just being made a little harder".

Regarding a 3 phase supply in domestic dwellings, your question is entirely sensible. We don't have it in ROI or UK "because...". You will hear plenty of reasons why its not a good ideabut no valid ones in my opinion. Lots of European countries have them and I see nothing but advantages.

 

[pc1966]

From an electrical safety point of view, I would have no concerns vi's, a vi's single module or double module rcbo, s. From an installation and maintenance (faultfinding) and testing point of view, (IR testing and neutral earth fault finding) I would suggest that dual module are a standout winner.

I think (not sure) that the original question being asked by @nicebutdim was more about single versus double width for the 1P+N style like the new Wylex, Crabtree, Fusebox RCBOs.

To me having neutral switch just make so much sense, for testing as you say, as well as for TT with any up-front delay RCD to provide selectivity on N-E faults.

I also agree that we should already have neutral as a bus-bar so you don't have the nest of RCBO tails to deal with.

 

[pc1966]

Regarding a 3 phase supply in domestic dwellings, your question is entirely sensible. We don't have it in ROI or UK "because...". You will hear plenty of reasons why its not a good ideabut no valid ones in my opinion. Lots of European countries have them and I see nothing but advantages.

It is not that uncommon to have 3-phase to domestic for higher power, but fairly unusual to have multiple phases around a house. Usually it is one phase for home, another for EV, etc., or the home is so large it has sub-DB per floor or wing, etc, and single-phase within there.

 

[nicebutdim]

I think (not sure) that the original question being asked by @nicebutdim was more about single versus double width for the 1P+N style like the new Wylex, Crabtree, Fusebox RCBOs.

To me having neutral switch just make so much sense, for testing as you say, as well as for TT with any up-front delay RCD to provide selectivity on N-E faults.

I also agree that we should already have neutral as a bus-bar so you don't have the nest of RCBO tails to deal with.

I was specifically wondering if there were any advantages from an electrical perspective, as the installation side was obvious enough, and wondered if I'd have gained any improvements on electrical safety by using 2 module RCBOs.

I should clarify that my mention of 3 phase was about the style of board, rather than the idea of 3 phase supplies. It makes sense that more space is beneficial for installation and maintenance.


I did once enquire about a 3 phase supply for a workshop at the same property, but the costs were astronomical - new poles, transformer, underground cables etc ?

 

[pc1966]

My original assumption was the double-width was for 2P OCPD action, so it needed 2 sets of thermal/magnetic trips and related arc-chutes, etc.

But given the Hager ones seem to 1P+N and presumably others for the EU are also that, I do wonder. Maybe just historically that was the space needed for the RCD electronics, etc?

 

[Mike Johnson]

My original assumption was the double-width was for 2P OCPD action, so it needed 2 sets of thermal/magnetic trips and related arc-chutes, etc.

That was certainly my assumption as well, but was educated on here about two years or so ago, I think by you PC1966 when you said that the N was just dragged along with the L when the thermal/magnetic trips operated, you have to wonder why they did that when there is obviously room inside for two trips, perhaps it's just cost?

I just had to modify my "year or so ago" to "two years or so ago" after realising I have lost a whole year due to the lockdown.??

 

[nicebutdim]

My original assumption was the double-width was for 2P OCPD action, so it needed 2 sets of thermal/magnetic trips and related arc-chutes, etc.

But given the Hager ones seem to 1P+N and presumably others for the EU are also that, I do wonder. Maybe just historically that was the space needed for the RCD electronics, etc?

That's were my questioning started: are 2 module breakers providing something more than single module breakers? The answer seems to be 'maybe, but not always'.

Single width with plug in busbars for L & N sounds like a good way forward...