TN-C-S (PEN) RCBOs Discussion

[Burnmenot]

I'm currently planning for a CU upgrade on the domestic premises, and following previous advice on this forum, I was told that I should consider upgrading to a Type A RCBO CU.
I have been doing a bit of reading and came across some confusing information, stating that an RCD would not work on a PEN system, RCCD was not permitted on a PEN system and consequently, RCBO would not work and it will have to have separate earth.

I believe I have a PEN system as the earth it's taken at the DSO service fuse, and I also seem to have a small green hatch on the ground for rod servicing...
I can add some photos for clarification if needed.

This is confusing to me as I do seem to have split distribution with an RCD protecting the socket rings, immersion, and boiler, and on the other side, all the light rings an RCBO for the shower.

I would appreciate any comments

 

[Soi disant]

I'm currently planning for a CU upgrade on the domestic premises, and following previous advice on this forum, I was told that I should consider upgrading to a Type A RCBO CU.

The "problem" there is that whatever your motive is for sitting down to think about whether Type AC is still suitable or not, and the process you go through which leads you to decide it isn't, if all that is done properly you might well find that Type A isn't suitable, and you need Type F, at least for some circuits.

I have been doing a bit of reading and came across some confusing information, stating that an RCD would not work on a PEN system, RCCD was not permitted on a PEN system and consequently, RCBO would not work and it will have to have separate earth.

Got a link to that? It must surely be talking about the situation where N & E remain combined throughout the installation....

 

[timhoward]

I think there is confusion and you might be thinking of comments that an RCD or RCBO wouldn’t protect you in the event of a broken supply Neutral in a TNCS system?

 

[Burnmenot]

The "problem" there is that whatever your motive is for sitting down to think about whether Type AC is still suitable or not, and the process you go through which leads you to decide it isn't, if all that is done properly you might well find that Type A isn't suitable, and you need Type F, at least for some circuits.


Got a link to that? It must surely be talking about the situation where N & E remain combined throughout the installation....

the last page of this Hager Tech datasheet mentions that RCCB is not permitted in PEN.
Aso this thread on the IET forum states that an RCD will not work on a PEN system: https://----------------------/discussions/viewtopic/1037/25035

regarding the comment you made about the type, being F perhaps more suitable for some circuits, I'd say that given all the modern equipment we have, (water pump, modern washing machines, dishwashers, and all the IT equipment) maybe even a type B may be more appropriated?

 

[Burnmenot]

I think there is confusion and you might be thinking of comments that an RCD or RCBO wouldn’t protect you in the event of a broken supply Neutral in a TNCS system?

thanks for your comment, I didn't really refer to that, I understand that is a very remote possibility.... to lose N and not lose L in the concentric cable from the DSO would be a very unlikely event.

 

[timhoward]

thanks for your comment, I didn't really refer to that, I understand that is a very remote possibility.... to lose N and not lose L in the concentric cable from the DSO would be a very unlikely event.

Sorry! I’ll read the stuff you posted later as it sounds interesting.

 

[Julie.]

I am very confused with what you are saying, and the links you have provided don't work.


You talk about having a TN-C-S - which obviously will have a PEN upstream, but then talk about the manual not allowing the use of any RCBO/RCCB in the PEN - why on earth would you want to put it in the PEN, this would clearly be prohibited?


You say you are looking to replace the CU, well that is the right place to put the RCCB/RCB/RCBOs, under no circumstances should you consider placing any of these in the PEN.

You need to get someone in to do this, just get the electrician to change the CU, you can use one that's fully populated with RCBOs, or get a split board with two or more RCD sections.

I would recommend type A RCD/RCBO, usually B curve RCBO/MCB - but your electrician will size them accordingly.

Edit:

Reading your post again, do you have a TN-C-S or TT - you also talk about having a Rod?

The protection requirements are different between TNCS and TT - although in both cases RCD/RCBO can be used in a TT you will need to use a RCD for fault protection (not additional), and usually a type S ahead of the CU

 

[timhoward]

The Hager document last page is saying you can’t have a PEN conductor downstream of the device, not you cant install a device on a TNCS system. They are basically saying that if any fault current returned via the same conductor as the N the device wouldn’t know it is fault current. You would never do this anyway.

 

[Burnmenot]

The Hager document last page is saying you can’t have a PEN conductor downstream of the device, not you cant install a device on a TNCS system. They are basically saying that if any fault current returned via the same conductor as the N the device wouldn’t know it is fault current. You would never do this anyway.

gotcha, thanks for the clarification, much appreciated

 

[Burnmenot]

I am very confused with what you are saying, and the links you have provided don't work.


You talk about having a TN-C-S - which obviously will have a PEN upstream, but then talk about the manual not allowing the use of any RCBO/RCCB in the PEN - why on earth would you want to put it in the PEN, this would clearly be prohibited?


You say you are looking to replace the CU, well that is the right place to put the RCCB/RCB/RCBOs, under no circumstances should you consider placing any of these in the PEN.

You need to get someone in to do this, just get the electrician to change the CU, you can use one that's fully populated with RCBOs, or get a split board with two or more RCD sections.

I would recommend type A RCD/RCBO, usually B curve RCBO/MCB - but your electrician will size them accordingly.

Edit:

Reading your post again, do you have a TN-C-S or TT - you also talk about having a Rod?

The protection requirements are different between TNCS and TT - although in both cases RCD/RCBO can be used in a TT you will need to use a RCD for fault protection (not additional), and usually a type S ahead of the CU

thanks for the comments, I appreciate I will have to get a RECI to do it, I'm just trying to understand what would suit better my needs ahead of the call, educating oneself about electricity and what goes on one's home never hurt anyone I believe.
I understand that I may have a TN-C-S system as the earth seems to come from the DSO service fuse, and I seem to have an earth rod too, I attach the pics for clarification.

 

[Rockingit]

You've a TN-C-S (aka PME) system and need to replace that 16mm T&E before worrying about anything else!

 

[Burnmenot]

You've a TN-C-S (aka PME) system and need to replace that 16mm T&E before worrying about anything els

oh ok, is there a problem with that wire?

 

[westward10]

The OP is in Southern Ireland where the TN-C-S is neutralised.

 

[Rockingit]

oh ok, is there a problem with that wire?

You'll need to consult with a reputable electrician to you, but in the U.K. that would not meet our regulations.

 

[Julie.]

oh ok, is there a problem with that wire?

Years ago it would be OK, now it either needs to be replaced by armoured, or surface/contained, depending on how far it goes it may need local protection (such as fuses etc), it also looks a little small - depends on your fuse size but it will be a maximum of 80A

 

[Burnmenot]

You'll need to consult with a reputable electrician to you, but in the U.K. that would not meet our regulations.

I will check, but just out of curiosity, why would they not comply? what is the problem?

 

[Burnmenot]

Years ago it would be OK, now it either needs to be replaced by armoured, or surface/contained, depending on how far it goes it may need local protection (such as fuses etc), it also looks a little small - depends on your fuse size but it will be a maximum of 80A

fuse is 63amp, so you mean that it would have to be on a metal earthed conduit? being concealed in the ESB box?

 

[Soi disant]

the last page of this Hager Tech datasheet mentions that RCCB is not permitted in PEN.

It is just as I suggested in #2. It's talking about PEN conductors - you don't have those in your system.

Your installation is not TN-C, it's TN-C-S. N & E become separate at the service head.

Aso this thread on the IET forum states that an RCD will not work on a PEN system: Electrical Blog - Electrical Advice | Free Electricians Advice Forum - https://electriciansforums.co.uk/discussions/viewtopic/1037/25035

regarding the comment you made about the type, being F perhaps more suitable for some circuits, I'd say that given all the modern equipment we have, (water pump, modern washing machines, dishwashers, and all the IT equipment) maybe even a type B may be more appropriated?

Unlikely - Type F will be OK for the sorts of loads you find in domestic installations, apart from EV charging points, but they're better off separated from the main house installation anyway.

 

[Julie.]

fuse is 63amp, so you mean that it would have to be on a metal earthed conduit? being concealed in the ESB box?

There are multiple options, much depends on how long the run is from the isolator to the cu, and where it is, if it is surface, that is different from concealed; but yes, if it is concealed one option is a metalic conduit.

This work is controlled in Ireland, so you need a fully qualified person to do the work, and they will cover this aspect as much as the actual cu replacement.

 

[Burnmenot]

There are multiple options, much depends on how long the run is from the isolator to the cu, and where it is, if it is surface, that is different from concealed; but yes, if it is concealed one option is a metalic conduit.

This work is controlled in Ireland, so you need a fully qualified person to do the work, and they will cover this aspect as much as the actual cu replacement.

I can see your point, the box was actually smashed to get the meter tails and the service cable, this is 1997... these houses were thrown together in a weekend, way overdue for an upgrade and an in-depth inspection, I will stop here, there are so many other aspects that would not be compliant with the latest regulations... I'm just afraid I'm going to have to rewire the whole house and it will cost me an eye and a leg ;-)

Thanks for your comments

 

[timhoward]

I can see your point, the box was actually smashed to get the meter tails and the service cable, this is 1997... these houses were thrown together in a weekend, way overdue for an upgrade and an in-depth inspection, I will stop here, there are so many other aspects that would not be compliant with the latest regulations... I'm just afraid I'm going to have to rewire the whole house and it will cost me an eye and a leg ;-)

Thanks for your comments

On a positive note it sounds like you have RCD protection for everything except lighting which is better than quite a few houses I see. A board change alone shouldn't be an eye and a leg, and your electrician will probably discuss options with you.

 

[LastManOnline]

You've a TN-C-S (aka PME) system and need to replace that 16mm T&E before worrying about anything else!

Only just saw OP is from Dublin. 16mm T&E is the standard supply in ROI (63 amp fuse) for domestic installations. TNC-S is the only supply type available for domestic installations in ROI. You have a standard 4 foot earth rod which is accessed via the "green hatch" because its obligatory in ROI. Your DB sounds standard.
Upgrading your DB to suitable rcbo, s is a good idea. Two things to be aware of are (1) a new set of regulations apply since February of this year and (2) carrying out any electrical works on a DB by anyone except a RECI registered electrician is against not just the regulations but also against the law. The "Safe Electric" website would be a really helpful guide for someone like yourself.

 

[Soi disant]

carrying out any electrical works on a DB by anyone except a RECI registered electrician is against not just the regulations but also against the law.

That's going to help who, how?

And is justified by what?

 

[westward10]

That's going to help who, how?

And is justified by what?

It is illegal in Southern Ireland to carry out certain electrical works unless you are an REC. It can result in heavy fines or imprisonment.

 

[LastManOnline]

That's going to help who, how?

And is justified by what?

Not sure of all the factors involved in getting us to this point.10 years ago there were a number of options on the table regarding the way forward for the electrical industry here(including the UK model). They chose ultimately to really tighten up in the domestic sector and to continue the traditional apprenticeship arrangement. It seems to be working well. I don't agree with some aspects. Not allowing qualified (but unregistered) electricians to work on their own CU, s is OTT in my opinion. There was an arrangement where they could get their work independently verified but that's now gone.

 

[i=p/u]

Some amount of junction boxes (oboes) sold in ROI. I'd say they have to take that stance, just to get the message out..

 

[pc1966]

Not sure of all the factors involved in getting us to this point.10 years ago there were a number of options on the table regarding the way forward for the electrical industry here(including the UK model). They chose ultimately to really tighten up in the domestic sector and to continue the traditional apprenticeship arrangement. It seems to be working well. I don't agree with some aspects. Not allowing qualified (but unregistered) electricians to work on their own CU, s is OTT in my opinion. There was an arrangement where they could get their work independently verified but that's now gone.

This is something I have wondered about. Forgive me for perhaps seeing national stereotypes here, but I have never seen the ROI as a country associated with "following orders" as one might do for, say Germany.

So the rather draconian limits on what folk can do with thier own electrics is a bit puzzling. Has there been a few high-profile cases of deaths, etc, related to pi**poor DIY work or similar to force the law there?

 

[LastManOnline]

This is something I have wondered about. Forgive me for perhaps seeing national stereotypes here, but I have never seen the ROI as a country associated with "following orders" as one might do for, say Germany.

So the rather draconian limits on what folk can do with thier own electrics is a bit puzzling. Has there been a few high-profile cases of deaths, etc, related to pi**poor DIY work or similar to force the law there?

You are correct, we can be pretty relaxed about breaking rules here, PROVIDING the principle remains intact i. e. crossing the road when there is no traffic around is fine regardless whether the "red" or "green" man is lit. A German probably would, nt do that.
But breaking rules that might lead to a potential for risk is a no-go. Electrical installation work is seen here as the preserve of qualified electricians only. Its very unusual for a lay person to carry out their own electrical work.And if they do, it tends to be frowned upon. Registered electricians can certify their own work only.There has always been a very cautious approach to electrics here (rcd, s mandatory since 1981,rewireable fuses banned long ago, all mcb boards became standard in 80,s). I have never experienced or heard of a work colleague who experienced an electrical fire. (I, m forty years in the game). I think this law is just another reflection of that cautious approach. I Don, t think it was necessary to make the regulations statutory
If you were to contrast how our electrical system is managed compared to our road infrastructure (shabby) it's like comparing chalk and cheese.

 

[Soi disant]

It is illegal in Southern Ireland to carry out certain electrical works unless you are an REC. It can result in heavy fines or imprisonment.

Yes.

That helps who, how?

And is justified by what?

 

[Soi disant]

You are correct, we can be pretty relaxed about breaking rules here, PROVIDING the principle remains intact i. e. crossing the road when there is no traffic around is fine regardless whether the "red" or "green" man is lit. A German probably would, nt do that.

I once casually strolled across a road in Munich with no traffic anywhere near, but against a red man. All the other people standing on the pavement looked at me as if I'd just bitten the head off a kitten.

Electrical installation work is seen here as the preserve of qualified electricians only.....I think this law is just another reflection of that cautious approach.

Or a reflection of very successful lobbying by the electrical industry.

It's a similar position in Australia. And it used to be in NZ. When NZ liberalised their regime and shut down the legally mandated closed shop, electrical "incidents" reduced. Fewer fires, fewer electrocutions.

 

[westward10]

Yes.

That helps who, how?

And is justified by what?

No idea what you are getting at.

 

[Risteard]

Or a reflection of very successful lobbying by the electrical industry.

Some would suggest that it has more to do with successful lobbying by the Revenue Commissioners. I'm not sure that I agree with them as it is a rather cynical view, but I suppose it's possible that there could be some truth to it.

 

[Risteard]

You'll need to consult with a reputable electrician to you, but in the U.K. that would not meet our regulations.

Old I.S. 201-4 16mm^2 T&E had a 10mm^2 protective conductor which meets the requirements for the main protective conductor (neutralising link). The newer 16mm^2 T&E (and even newer LSF version (minimum Dca, -s2, d2, a2) which needs to be used now) has a 16mm^2 protective conductor, which is also insulated.

 

[LastManOnline]

Or a reflection of very successful lobbying by the electrical industry.

I do agree that there is likely an element of that involved as well. I felt like that when the PIR, s(periodic inspection reports) were first introduced. The idea of "taking apart" a privately owned, 5 year old home by subjecting it to the same exhaustive testing as we would a newly installed electrical installation never felt right.
Its different for rented accomodation (especially student accomodation). But I still think that a 5 year old home should not require every accessory to be disconnected, inspected, IR tested etc. An experienced visual inspection combined with checking and testing of all safety devices and earthing would suffice in my opinion

 

[i=p/u]

And that's what the books tell you... you as the inspector decide..

 

[LastManOnline]

, but I have never seen the ROI as a country associated with "following orders" as one might do for, say Germany.

This came into my mind today and I had to laugh. "Following orders" is definitely more of a Germanic trait than an Irish one. However the Irish electrical system has always had a significant German input. I have learned recently that you DO NOT question the electrical regs in ROI.You "follow orders". In less than a year I have being removed from one forum, sanctioned in a second forum and politely told to "shut it" in a third forum (by fellow sparks) for doing precisely that. The German influence?? possibly

 

[nicebutdim]

This came into my mind today and I had to laugh. "Following orders" is definitely more of a Germanic trait than an Irish one. However the Irish electrical system has always had a significant German input. I have learned recently that you DO NOT question the electrical regs in ROI.You "follow orders". In less than a year I have being removed from one forum, sanctioned in a second forum and politely told to "shut it" in a third forum (by fellow sparks) for doing precisely that. The German influence?? possibly

Questions about PEN faults?

 

[LastManOnline]

Questions about PEN faults?

Yes. Among others.

 

[nicebutdim]

Yes. Among others.

I like that you're inclined to question that which doesn't sit right with you, but I can see how it might not go down well where rules are to be followed and not questioned.

Maybe those who object to your questions might ask themselves how those rules came about in the first instance...

 

[LastManOnline]

I like that you're inclined to question that which doesn't sit right with you, but I can see how it might not go down well where rules are to be followed.

I understand their reaction. What I, m inclined to do (I do the same on this forum) is sometimes to focus attention at other countries work practices and ask if " could we perhaps learn from that?" Sometimes its appreciated, sometimes it's not. My post about the shortcomings of TNC-S went down like a lead balloon. I was removed from the site. A few weeks later a newsletter from "Safe Electric" addressed the topic directly. Co-incidence?

 

[pc1966]

I too like to see how things are done elsewhere as every country's system is a mixture of good and bad, and largely not that planned either (i.e. often things had to follow on from past installations & standards).

The TN-C-S open PEN risk is something that looks like becoming a topic as more folk look to EV chargers. I suspect there won't be and change to TN-C-S usage by the DNO as it is widespread and cheap, but I think inevitably EV chargers will all have to be Zappi-like in protecting against open PEN risk without an earth rod, as driving in rods in urban areas is going to cause all sorts of practical issues and damaged utility cables/pipes.

The ROI practice of having rods for the TN-C-S earth locally makes a lot of sense, though I doubt that 1.2m rods are meaningfully low to help much. The discussed option in AM2 for our 18th to make it part of foundations makes more sense, as it could be well under 10 ohms that way, but that will take years (if ever) to make much difference considering it won't be retro-fitted to the majority of housing.

 

[LastManOnline]

I too like to see how things are done elsewhere as every country's system is a mixture of good and bad

"A mixture of good and bad" sums it up well. I like to start a discussion on the "bad" to explore how it might be improved.

I suspect there won't be and change to TN-C-S usage by the DNO as it is widespread and cheap.

No. Its here to stay. So with that in mind lets educate people about the shortcomings of the system and that could go a long way in mitigating the risks associated with it.

The ROI practice of having rods for the TN-C-S earth locally makes a lot of sense, though I doubt that 1.2m rods are meaningfully low to help much.

They will help in reducing touch voltage to some extent. What is unfortunate about them is that in almost every country that uses them (ROI, AUS, NZ etc) in their TNC-S supply system, there is this misunderstanding that the 4 foot rod is a "back up" under open PEN faults. This misinformation is widespread. I have encountered it in discussions with inspectors and educators. I, m a, little baffled by that.

. The discussed option in AM2 for our 18th to make it part of foundations makes more sense, as it could be well under 10 ohms that way,

Makes good sense.

 

[pc1966]

What is unfortunate about them is that in almost every country that uses them (ROI, AUS, NZ etc) in their TNC-S supply system

I think the USA has two rods, spaced apart (8 feet?) but again 4 foot deep is not going to give you any meaningfully low earth Ra value.

Historically the metal service pipes did give you a decent earth, and often backup connectivity between supply E (i.e. PEN) bonds, but they are of course all being converted to plastic.

 

[LastManOnline]

I think the USA has two rods, spaced apart (8 feet?) but again 4 foot deep is not going to give you any meaningfully low earth Ra value.

I stand to be corrected here but my recollection is that the Americans use as you correctly say, 2 rods, but I think they are longer than 4 feet. In any case I know they do a better job with their rods than we do.

Historically the metal service pipes did give you a decent earth, and often backup connectivity between supply E (i.e. PEN) bonds, but they are of course all being converted to plastic.

This has been the single most important factor in the introduction of our TNC-S system. I can appreciate that in the late 80,s when plastic started to replace metal services there was a major recession going on. There possibly was, nt the money to pay for anything other than TNC-S, the cheapest supply system available.