what constitutes a new circuit?

[ban-all-sheds]

So would that be the same sort of common sense which you believe you applied when you said that installing an MCB into an empty slot in a CU and installing new cabling from the newly installed MCB would be "extending an existing circuit"?

 

[JohnW2]

So would that be the same sort of common sense which you believe you applied when you said that installing an MCB into an empty slot in a CU and installing new cabling from the newly installed MCB would be "extending an existing circuit"?

If you're talking about a 'primary' CU, where do you think I said that? Connecting new wiring to a new MCB in a 'primary' is obviously a 'new circuit' by anyone's definition.

If you are talking about a 'secondary' CU (e.g. in a garage), downstream of a primary one, then it's the sort of common sense which doesn't see why replacing the garage CU with a JB (or direct connection of the feed to a socket) would create a materially different situation - the same sort of common sense which says that connecting something via an FCU does not create a new circuit.

Kind Regards, John

 

[ban-all-sheds]

The trouble here is that you are on the one hand complaining that the lack of definitions other than those in BS 7671 creates scenarios which you believe would not exist were common sense to apply, and on the other hand as part of your suggested "common sense approach" you are using terms which have no definitions.

Like "primary CU" and "secondary CU".

And I don't see much common sense in the notion that there is no material difference between a CU and a JB.

 

[JohnW2]

The trouble here is that you are on the one hand complaining that the lack of definitions other than those in BS 7671 creates scenarios which you believe would not exist were common sense to apply, and on the other hand as part of your suggested "common sense approach" you are using terms which have no definitions. ... Like "primary CU" and "secondary CU".

That's why I put them in quotes, but I'll happily provide my 'common sense' definitions - a 'primary' CU/DB is the first one downstream of the service fuse and any other single OPD (like a switch-fuse), and a 'secondary' CU/DB is one fed from an OPD in a 'primary' one.

And I don't see much common sense in the notion that there is no material difference between a CU and a JB.

I didn't say that. I said that they "didn't create materially different situations". It makes absolutely no sense that bypassing the OPD in a ('secondary') CU could turn notifiable work into non-notifiable work.

Kind Regards, John

 

[ban-all-sheds]

That's why I put them in quotes, but I'll happily provide my 'common sense' definitions - a 'primary' CU/DB is the first one downstream of the service fuse and any other single OPD (like a switch-fuse), and a 'secondary' CU/DB is one fed from an OPD in a 'primary' one.

OK.

So if we can put to one side for a moment the definition of "circuit" what is the material difference between the following:

A circuit originating at an MCB in a CU which is directly downstream of the service fuse.

A circuit originating at an MCB in a CU which is directly downstream of a switchfuse.

A circuit originating at an MCB in a CU which is directly downstream of an MCB or RCBO in a small enclosure containing nothing else and supplying nothing else.

A circuit originating at an MCB in a CU which is directly downstream of an RCBO or MCB in another CU.

If there are material differences, do any of them result in different parameters for circuit design, different testing or a different form of BS 7671 certification?

It makes absolutely no sense that bypassing the OPD in a ('secondary') CU could turn notifiable work into non-notifiable work.

It also makes absolutely no sense that if something is notifiable then changing the nature of a protective device upstream of the CU could make it non-notifiable.

 

[JohnW2]

OK. ... So if we can put to one side for a moment the definition of "circuit" what is the material difference between the following:
(a)... A circuit originating at an MCB in a CU which is directly downstream of the service fuse.
(b)... A circuit originating at an MCB in a CU which is directly downstream of a switchfuse.
(c)... A circuit originating at an MCB in a CU which is directly downstream of an MCB or RCBO in a small enclosure containing nothing else and supplying nothing else.
(d)... A circuit originating at an MCB in a CU which is directly downstream of an RCBO or MCB in another CU.

I agree that there is not a lot of difference. Scenarios (a), (b) and (c) are certainly effectively identical - in all cases you are talking about a final circuit originating from an MCB/RCBO in what I would call a 'primary' CU.

However, (d) seems a bit different to me, since it is analogous to having something fed by an FCU connected to a circuit originating from a 'primary' CU. However, as I've implied, if you feel that connecting something to an existing circuit via an FCU is notifiable, then you obviously would think the same about a 'secondary' CU.

... but do you really believe that connecting something to an existing circuit via an FCU is notifiable (or was 'intended to be' notifiable)?

Kind Regards, John

 

[ban-all-sheds]

However, (d) seems a bit different to me, since it is analogous to having something fed by an FCU connected to a circuit originating from a 'primary' CU.

So a ring final connected to a 32A MCB in CU B is analogous to having something fed by an FCU connected to a circuit originating from CU A as long as CU B is supplied from an MCB in CU A. But if CU B was supplied from the same MCB housed in a small enclosure rather than a large one it would not be analogous?

However, as I've implied, if you feel that connecting something to an existing circuit via an FCU is notifiable, then you obviously would think the same about a 'secondary' CU.

For that to be true I would have to understand what could be meant by "primary" and "secondary" CU, and it would have to be "meant" in a way which could be unambiguously defined, logical, and made engineering sense. And at the moment I don't have that understanding.

but do you really believe that connecting something to an existing circuit via an FCU is notifiable (or was 'intended to be' notifiable)?

The answer to that is that in the absence of any alternative authoritative definition to the one in BS 7671, yes (and no).

But trying to introduce a totally unprecedented and unofficial concept of "primary" and "secondary" CUs which as soon as you actually examine it falls apart and makes less sense than the problem you are trying to resolve by it is not the answer.

You seem to have boarded a flight of fancy which is heading for the wrong destination.

 

[JohnW2]

However, as I've implied, if you feel that connecting something to an existing circuit via an FCU is notifiable, then you obviously would think the same about a 'secondary' CU.

For that to be true I would have to understand what could be meant by "primary" and "secondary" CU, and it would have to be "meant" in a way which could be unambiguously defined, logical, and made engineering sense. And at the moment I don't have that understanding.

I don''t think it's true that you would need to understand anything about what I've been calling 'primary' and 'secondary' CUs. IF you really believe that connecting something via an FCU creates a new circuit (which therefore requires notification), it would surely follow that you would regard connecting anything to a (previously unused) MCB/RCBO of any CU (no matter how described or wired) as also creating a new circuit?

but do you really believe that connecting something to an existing circuit via an FCU is notifiable (or was 'intended to be' notifiable)?

The answer to that is that in the absence of any alternative authoritative definition to the one in BS 7671, yes (and no).

This is where I believe that 'common sense' has to be applied. I agree that if one attempts to use existing BS7671 definitions in order to interpret the Building Regs (not that such is a very logical, or necessary reasonable, thing to do), then one comes to the conclusions that connecting anything via an FCU is notifiable. However, since we seem to be agreed that this was almost certainly not the intention of whoever wrote the Building Regs, the conclusion would seem to be that the BS7671 definition of 'a circuit' is not applicable to the Building Regs, leaving us with the only way of interpreting the Building Regs as being the application of 'common sense' and our belief about what was (or was not) the intention of those who wrote the Building Regs.

What alternative is there? Nothing in the Building Regs says that they are using BS7671 definitions, so why should we attempt to use (essentially arbitrarily) those definitions to help us interpret the Building Regs? We could, I would say at least as reasonably, decide to use the OED (or maybe IEC) definition (whatever they may be).

Kind Regards, John

 

[ban-all-sheds]

I don''t think it's true that you would need to understand anything about what I've been calling 'primary' and 'secondary' CUs. IF you really believe that connecting something via an FCU creates a new circuit (which therefore requires notification), it would surely follow that you would regard connecting anything to a (previously unused) MCB/RCBO of any CU (no matter how described or wired) as also creating a new circuit?

I do believe that both create a New_CircuitBS7671. And I do agree that it surely cannot have been the intention that the former should create a New_CircuitBUILDING_REGULATIONS.

What I don't understand is the idea that if the CU is supplied through a protective device then there is the possibility that the latter might not be a new circuit, or that the new/not new decision would rest on the type of that protective device or the size of its enclosure.

This is where I believe that 'common sense' has to be applied. I agree that if one attempts to use existing BS7671 definitions in order to interpret the Building Regs (not that such is a very logical, or necessary reasonable, thing to do),

It could be logical but unreasonable.

then one comes to the conclusions that connecting anything via an FCU is notifiable.

Indeed.

However, since we seem to be agreed that this was almost certainly not the intention of whoever wrote the Building Regs, the conclusion would seem to be that the BS7671 definition of 'a circuit' is not applicable to the Building Regs,

Indeed.

leaving us with the only way of interpreting the Building Regs as being the application of 'common sense' and our belief about what was (or was not) the intention of those who wrote the Building Regs.

Indeed.

What do you believe was their intention regarding the notifiability of new circuits originating at a CU?

What alternative is there? Nothing in the Building Regs says that they are using BS7671 definitions, so why should we attempt to use (essentially arbitrarily) those definitions to help us interpret the Building Regs?

Because on the face of it it doesn't seem unreasonable to use BS 7671 for the definition of electrical terms when compliance with BS 7671 is the default and most likely route to compliance with the Building Regulations?

We could, I would say at least as reasonably, decide to use the OED (or maybe IEC) definition (whatever they may be).

I've looked at 3 dictionaries - Collins English Dictionary 21st Century Edition, the Oxford Reference Dictionary and the Shorter OED (ironically only "shorter" when compared to the 20-volume OED).

None are much help - they either don't rule out an FCU creating a circuit, or mean that you'd have to consider everything back at least as far as the substation, or are hopelessly vague, e.g. "the path of a current".

 

[JohnW2]

I don''t think it's true that you would need to understand anything about what I've been calling 'primary' and 'secondary' CUs. IF you really believe that connecting something via an FCU creates a new circuit (which therefore requires notification), it would surely follow that you would regard connecting anything to a (previously unused) MCB/RCBO of any CU (no matter how described or wired) as also creating a new circuit?

I do believe that both create a New_CircuitBS7671. And I do agree that it surely cannot have been the intention that the former should create a New_CircuitBUILDING_REGULATIONS.

I'm pleased to hear that we agree about that much.

What I don't understand is the idea that if the CU is supplied through a protective device then there is the possibility that the latter might not be a new circuit, or that the new/not new decision would rest on the type of that protective device or the size of its enclosure.

You say you don't understand that - but isn't that actually your view or what the BR 'intended'? Perhaps I've misunderstood but I thought that your view was (as above) that the BR did not intend that (in terms of notifiability) an FCU should create a new circuit, BUT that an MCB in a 'secondary' CU (e.g. in garage, fed from house CU) did create a new circuit. Is that your view of their intent? If it is, the only difference between the two situations is the nature of the OPD and the nature/size of the enclosure in which it exists.

What alternative is there? Nothing in the Building Regs says that they are using BS7671 definitions, so why should we attempt to use (essentially arbitrarily) those definitions to help us interpret the Building Regs?

Because on the face of it it doesn't seem unreasonable to use BS 7671 for the definition of electrical terms when compliance with BS 7671 is the default and most likely route to compliance with the Building Regulations?

You're not eric You know as well as I do that the Building Regs (i.e. Part P) say nothing about BS7671, so I'm not sure that it is necessarily that reasonable to assume that a BS7671 definition can be applied to the Building Regs - particularly if applying that definition means that the Building Regs would be saying something which neither of us (and few others, I imagine) believe is what they intended.

I've looked at 3 dictionaries - Collins English Dictionary 21st Century Edition, the Oxford Reference Dictionary and the Shorter OED (ironically only "shorter" when compared to the 20-volume OED). None are much help - they either don't rule out an FCU creating a circuit, or mean that you'd have to consider everything back at least as far as the substation, or are hopelessly vague, e.g. "the path of a current".

I feared that might be the case. I actually doubt whether it would be possible to devise a definition that would suit the purposes of the BR without explicitly and specifically talking about things like CUs.

Kind Regards, John

 

[ban-all-sheds]

You say you don't understand that - but isn't that actually your view or what the BR 'intended'? Perhaps I've misunderstood but I thought that your view was (as above) that the BR did not intend that (in terms of notifiability) an FCU should create a new circuit, BUT that an MCB in a 'secondary' CU (e.g. in garage, fed from house CU) did create a new circuit.

Secondary, primary, tertiary, quaternary, quinary... their sequence of dependence is irrelevant - if it originates from a CU is is, I believe, what the BR means by "circuit".

And if you want to apply common sense, it's what people mean when they talk about a socket circuit, a lighting circuit, a cooker circuit, a shower circuit etc.

If you want to admit the legitimacy of BS 7671 for definitions, it's what goes onto the schedule of circuits on an EIC.

Is that your view of their intent? If it is, the only difference between the two situations is the nature of the OPD and the nature/size of the enclosure in which it exists.

That is my view of their intent, unless you can convince me that

(a) the installation of a new circuit;

means nothing at all, and is redundant, because there is no such thing as a new circuit.

What you are doing is looking at the same underlying problem, that of there being no definition of circuit which excludes an FCU but includes an MCB in a CU, from another angle. The problem does not mean that both a new run of cable from an FCU and one from an MCB are notifiable, nor that neither are. It means that they have not successfully codified their intention that one is not and the other is.

You're not eric You know as well as I do that the Building Regs (i.e. Part P) say nothing about BS7671, so I'm not sure that it is necessarily that reasonable to assume that a BS7671 definition can be applied to the Building Regs - particularly if applying that definition means that the Building Regs would be saying something which neither of us (and few others, I imagine) believe is what they intended.

I know that they don't say anything abut Part P, but given that the advice by the Secretary of State is that BS 7671 should be followed, that's why I said that on the face of it it doesn't seem unreasonable to use BS 7671 for the definition of electrical terms.

In this case, of course, it doesn't help because of the BS 7671 definition of 'circuit', but that doesn't affect the principle that using BS 7671 definitions is not obviously unreasonable.

Maybe it would have helped if the Building Regulations had used the term "new final circuit"?

I feared that might be the case. I actually doubt whether it would be possible to devise a definition that would suit the purposes of the BR without explicitly and specifically talking about things like CUs.

And FCUs.

Which it used to, until they "improved" it.

 

[JohnW2]

Perhaps I've misunderstood but I thought that your view was (as above) that the BR did not intend that (in terms of notifiability) an FCU should create a new circuit, BUT that an MCB in a 'secondary' CU (e.g. in garage, fed from house CU) did create a new circuit.... Is that your view of their intent? If it is, the only difference between the two situations is the nature of the OPD and the nature/size of the enclosure in which it exists.

That is my view of their intent, unless you can convince me that ....

Fair enough, but that doesn't really result in a very 'common sense' situation, does it? Starting with the simplest case ... consider a 'garage CU' fed from an 'existing circuit' originating at an MCB in the house CU, which contained a 6A MCB (for lighting) and a 10A MCB (the owner's requirements were very modest!) feeding just one socket. Would it make sense that (presumably because of the nature of the OPD and the enclosure in which they were contained) the wiring attached to those MCBs would be notifiable, given that the electrically identical situation with two FCUs would (per our understanding of 'intent') not be notifiable. ... and, if that would not make sense, would it make sense for the former to become notifiable if the sockets MCB increased to 20A or even 32A? I think the truth probably is that they did not even give enough though to what they intended to be notifiable. let alone finding a way of expressing it clearly.

I feared that might be the case. I actually doubt whether it would be possible to devise a definition that would suit the purposes of the BR without explicitly and specifically talking about things like CUs.

And FCUs.

Whoops As you undoubtedly realised, that's what I intended to type, but my finger seems to have missed the 'F'!

Kind Regards, John

 

[ban-all-sheds]

Fair enough, but that doesn't really result in a very 'common sense' situation, does it?

Yes. Unless you think it not commonsense that new circuits from a CU are intended to be notifiable whereas stuff from an FCU is not.

Starting with the simplest case ... consider a 'garage CU' fed from an 'existing circuit' originating at an MCB in the house CU, which contained a 6A MCB (for lighting) and a 10A MCB (the owner's requirements were very modest!) feeding just one socket. Would it make sense that (presumably because of the nature of the OPD and the enclosure in which they were contained) the wiring attached to those MCBs would be notifiable, given that the electrically identical situation with two FCUs would (per our understanding of 'intent') not be notifiable.

Absolutely. Unless you think it doesn't make sense that new circuits from a CU are intended to be notifiable whereas stuff from an FCU is not.

Unless you don't think it makes sense that an EIC schedule requires you to list circuits originating from a CU but doesn't require you to list spurs.

and, if that would not make sense, would it make sense for the former to become notifiable if the sockets MCB increased to 20A or even 32A?

But it does make sense, therefore your question about an irrelevant increase in the In of the breakers is moot.

I think the truth probably is that they did not even give enough though to what they intended to be notifiable. let alone finding a way of expressing it clearly.

No and yes.

I think that they knew full well what they intended to be notifiable, so much so that to them it was so obvious what it was that they didn't give anywhere near enough thought to expressing it in a way which was not open to interpretation. And I see not one thing wrong with, and everything right with, the intention that a spur should not be notifiable but a new final circuit from a CU should be.

No matter how that CU is supplied.

Whoops As you undoubtedly realised, that's what I intended to type, but my finger seems to have missed the 'F'!

I didn't really think about it, and if you had written '... things like FCUs' I would have written 'And CUs'.

 

[JohnW2]

Starting with the simplest case ... consider a 'garage CU' fed from an 'existing circuit' originating at an MCB in the house CU, which contained a 6A MCB (for lighting) and a 10A MCB (the owner's requirements were very modest!) feeding just one socket. Would it make sense that (presumably because of the nature of the OPD and the enclosure in which they were contained) the wiring attached to those MCBs would be notifiable, given that the electrically identical situation with two FCUs would (per our understanding of 'intent') not be notifiable.

Absolutely. Unless you think it doesn't make sense that new circuits from a CU are intended to be notifiable whereas stuff from an FCU is not.

That's where we differ. To me it makes no sense that a circuit is notifiable if it originates from an MCB or fuse within one sort of box but not notifiable if it originates from a fuse in another sort of box (assuming that both boxes get their supply from the same 'existing' circuit). I would be interested to know what makes you think that makes sense?

Kind Regards, John

 

[ericmark]

For it to be a new circuit the MCB/Fuse/RCD or the slot where it is fitted must have not been used before.

To show that's the case you need to view all the installation certificates from the time when the consumer unit or other device containing a fuse/MCB/RCD/RBCO was fitted.

If the LABC keeps those records then one could show if a new circuit or not. But if you need to contact every electrician who has worked on the installation to view the records then it's not really an option except in extreme circumstances i.e. a death. Even then it would be hard to show a circuit has never existed in the past.

So in real terms just not workable.