Cpc size on unfused spur

[EFLImpudence]

I'm also aware of fusing factors, but I am not seeing the death of rings.

You won't; just as you won't see 6mm² stop being used for 32A cooker circuits (the requirement for 30A/3036s).

People do what people have always done so that's what people do because that's what people do.

Although, having said that, I note from reading other forums that 10mm² is becoming fashionable for cooker circuits; promoted by those who understand even less.


As for the ring regulations (in addition to what John wrote) the regulation 433.1.204 is still written for 3036 fuses with their 0.725 derating factor.
A 3036/30A radial would require 6mm² cable.
It has not been updated for MCBs where a 40A would be compliant with 2.5mm², or 1.5mm² would be compliant with the 20A minimum CCC.

So, as 433.1.204 stands, the ring is of so little advantage that radials would be far better. Either 25A/2.5mm² (certainly adequate for areas other than the kitchen), or 32A/4mm² for kitchen.

 

[JohnW2]

Although, having said that, I note from reading other forums that 10mm² is becoming fashionable for cooker circuits; promoted by those who understand even less.

I don't know about 'becoming fashionable'. I inherited two of those (well, probably the imperial equivalents) 30 years ago, and one of them (because it was conveniently located) still feeds a 'lollipop' circuit in my cellar!

Kind Regards, John

 

[ban-all-sheds]

regulation 433.1.204 is still written for 3036 fuses with their 0.725 derating factor.

In what way?

It's written for ring circuits where Iz < In. The minimum Iz of 20A may be the Iz for a combination of Method C and a 3036 (just), but it also allows for Method A, 100# and 102# on MCBs.

So, as 433.1.204 stands, the ring is of so little advantage that radials would be far better. Either 25A/2.5mm² (certainly adequate for areas other than the kitchen), or 32A/4mm² for kitchen.

I've been saying for years that rings should be deprecated.

 

[EFLImpudence]

In what way?

As I wrote above.
Has it changed since the introduction of MCBs?

It's written for ring circuits where Iz < In. The minimum Iz of 20A may be the Iz for a combination of Method C and a 3036 (just), but it also allows for Method A, 100# and 102# on MCBs.

Why? I don't know if that is the reason it is as it is. Why would it be?
Which other circuit arrangement mandates the use of larger conductors permanently to accommodate possible occasional installation methods?
Do you have any evidence it is not just coincidence (apart from the tweaked one)?
Is it not that 20/0.725 = 27.586 (2.5mm² or the imperial equivalent)

I've been saying for years that rings should be deprecated.

Scousespark has obviously missed that.

 

[scousespark]

I asked EFLI questions in direct relation to one post.

In answer to a question about the tem spour in domestic environemnts, EFLI posted
Not necessarily - it is also called 'branch' on a radial. I don't know why.

I had read this as being a reference to the term branch being used as an alternartive to spur, applyng to a radial circuit. I think I have misinterpreted this.
If we break into cable, at any point (even at the OPD), we create what BS7671 refers to as a spur. We don't have forks, or offshoots, or branches. The term spur, is what is used by electricians.


The Ring Final (as specifically allowed) is virtually obsolete since MCBs.
I don't know why anyone would bother with it in a commercial installation.
My other question was why the arrival of MCB has made rings obsolete. I'm still not sure why an MCB would lead to a decision to no longer install rings.

I was not being smart here, just asking a couple of questions.

 

[scousespark]

As I wrote above.
Has it changed since the introduction of MCBs?


Why? I don't know if that is the reason it is as it is. Why would it be?
Which other circuit arrangement mandates the use of larger conductors permanently to accommodate possible occasional installation methods?
Do you have any evidence it is not just coincidence (apart from the tweaked one)?
Is it not that 20/0.725 = 27.586 (2.5mm² or the imperial equivalent)





Scousespark has obviously missed that.

I have seen this many times, but it is just opinion. There are pros and cons and installing a ring is still compliant with BS7671. Some electricians don't like rings and others do. The reality is that the main concerns are not wth the initial installation but rather with future changes introducing problems. FYI, my personal preference is that I'm happy installing either circuit.

 

[JohnW2]

I had read this as being a reference to the term branch being used as an alternartive to spur, applyng to a radial circuit. I think I have misinterpreted this.

Yes, I think there has probably been a misunderstanding. As I presume we all accept and agree, BS761 says that "spur" means a 'branch', or either a radial or ring circuit.

If we break into cable, at any point (even at the OPD), we create what BS7671 refers to as a spur. We don't have forks, or offshoots, or branches. The term spur, is what is

used by electricians.

Well, BS 7671 obviously recognises the concept of a 'branch' (even if in an 'everyday' sense) - since, as above, it defines a spur as being a branch (of a radial or ring circuit).

If we break into cable, at any point (even at the OPD), we create what BS7671 refers to as a spur.

We do - but, as I said, in the case of a radial, that is an unworkable definition, even if it is what the authors of BS 7671 have chosen to write. Taking the simplest possible example (to save time!), what cable has been 'broken into', and which is "the spur which has been created" (B or C)? ...

Kind Regards, John

 

[ban-all-sheds]

As I wrote above.

Here we go again.

What you wrote above was an assertion with no explanation or evidence to support it.

If you had explained in what way regulation 433.1.204 is still written for 3036 fuses with their 0.725 derating factor it would not have been necessary to ask.

Has it changed since the introduction of MCBs?

No.

Why should it?

A ring allows a circuit with a larger In than the Iz of the cable would normally support. Whatever the protective device, Iz must be ≥ 20A. It really doesn't matter what the factors are that reduce a cable's CCC - they are what they are, and if they bring Iz down to < 20A you may not use that cable, and if they don't, you may. (Subject to it meeting the minimum csa requirement as well).

Why? I don't know if that is the reason it is as it is. Why would it be?

I wasn't suggesting that is the reason, just pointing out that the minimum is 20A, and that is 27 derated by .725. But it wasn't chosen because that's what it is. It used to be Iz ≥ 0.67In and in 16th AMD1, after much jiggery-pokery they changed it to 20A.

How the original 0.67In figure was arrived at IHNI, but if you can find a copy of the "Amendment No 1 2002 to BS 7671 and ring circuits" article from Spring 2002 Wiring Matters you can read a recipe for fudge an explanation of the engineering work that went into establishing a fixed limit of 20A. It's no longer online at the IET - they apparently do not understand the idea of history.

Whatever factors apply to given cable installation, you're either going to be above 20A, or below. It so happens that 2.5mm² Method C is OK if you're using 3036s, but Method A would not be. Method A is OK if you're using an MCB. If you want a ring using a 3036 device, and the cable is Method 103# then you'll have to use 10mm².

Which other circuit arrangement mandates the use of larger conductors permanently to accommodate possible occasional installation methods?

Don't know what you mean. Is this to do with the explicit requirement for 2.5mm² even though 1.5mm² might do?

Do you have any evidence it is not just coincidence (apart from the tweaked one)?

Is it not that 20/0.725 = 27.586 (2.5mm² or the imperial equi valent)

I've got no evidence that it is, or is not, just coincidence.

 

[EFLImpudence]

Here we go again.
What you wrote above was an assertion with no explanation or evidence to support it.
If you had explained in what way regulation 433.1.204 is still written for 3036 fuses with their 0.725 derating factor it would not have been necessary to ask.

How about - because 433.1.204 specifically mentions them along with other OPDs?
Therefore, if the circuit is compliant with 3036s then it is excessive for MCBs.

No.
Why should it?

Because MCBs have less onerous circuit design requirements than 3036s.

A ring allows a circuit with a larger In than the Iz of the cable would normally support. Whatever the protective device, Iz must be ≥ 20A. It really doesn't matter what the factors are that reduce a cable's CCC - they are what they are, and if they bring Iz down to < 20A you may not use that cable, and if they don't, you may. (Subject to it meeting the minimum csa requirement as well).

It's all very well laying out the requirements but then to negate them by having to add "Subject to it meeting the minimum csa requirement as well" would appear to render the requirements pointless.

I wasn't suggesting that is the reason, just pointing out that the minimum is 20A, and that is 27 derated by .725. But it wasn't chosen because that's what it is. It used to be Iz ≥ 0.67In and in 16th AMD1, after much jiggery-pokery they changed it to 20A.

Aren't you confusing two separate things?
The 20A is 66.7% of the 30A (3036) rating and the need for 2.5mm² (with 27A CCC) is because of the 3036 0.725 derating.

How the original 0.67In figure was arrived at IHNI,

Neither do I. I am not arguing about that. I accept that there is a valid reason for it.
It does, though, mean a 40A MCB would be satisfactory on a ring.

but if you can find a copy of the "Amendment No 1 2002 to BS 7671 and ring circuits" article from Spring 2002 Wiring Matters you can read a recipe for fudge an explanation of the engineering work that went into establishing a fixed limit of 20A. It's no longer online at the IET - they apparently do not understand the idea of history.

As above. 66.7% of 30A.

Whatever factors apply to given cable installation, you're either going to be above 20A, or below. It so happens that 2.5mm² Method C is OK if you're using 3036s, but Method A would not be. Method A is OK if you're using an MCB. If you want a ring using a 3036 device, and the cable is Method 103# then you'll have to use 10mm².

Exactly. So I am correct.

Don't know what you mean. Is this to do with the explicit requirement for 2.5mm² even though 1.5mm² might do?

Yes. Although for 32A MCBs shouldn't it be a CCC of (32*66.7%) 21.33A?
I presume they must have thought that near enough in view of the conservative CCC figures.

I've got no evidence that it is, or is not, just coincidence.

I think I have - logic.

 

[ban-all-sheds]

How about - because 433.1.204 specifically mentions them along with other OPDs?

It lists all acceptable OPDs.

It makes as much sense to say that therefore 433.1.204 is still written for 3036 fuses than it does to say it is still written for any other type of device.

Interesting to note though that BS3871 devices are not allowed.

Therefore, if the circuit is compliant with 3036s then it is excessive for MCBs.

That applies to all circuits because of the nature of 3036s, not because of the circuit topology.

Because MCBs have less onerous circuit design requirements than 3036s.

Iz has to be 20A. It doesn't matter what the type of device is, it has to be 20A. The less onerous requirements of MCBs vs 3036s means that you can use 2.5mm² cable with MCBs when you might not with fuses due to installation method.

It's no different from any circuit where you need a given Iz - if your device is a 3036 fuse then sometimes you'll need a larger cable than you would if it were an MCB.

It's all very well laying out the requirements but then to negate them by having to add "Subject to it meeting the minimum csa requirement as well" would appear to render the requirements pointless.

Don't shoot the messenger. 433.1.204 imposes a minimum csa. It just does. I understand why just as much as I understand Table 52.3, which equally "renders pointless" Ib ≤ In ≤ Iz requirements.

Aren't you confusing two separate things?

No, because I have no evidence that it is anything more than coincidence.

The 20A is 66.7% of the 30A (3036) rating

It's ⅔ of any 30A device, irrespective of any device characteristics which affect cable ratings.

and the need for 2.5mm² (with 27A CCC) is because of the 3036 0.725 derating.

Yes, if that factor applies. And the need for 2.5mm² (with 27A CCC) is because of the derating which has to be applied for Reference Method A if that applies.

It does, though, mean a 40A MCB would be satisfactory on a ring.

It wouldn't, because BS 1363 accessories are not rated to have 27A in the cable they are connected to,

As above. 66.7% of 30A.

20A is ⅔ of 30A. But 20A was not chosen because it is.

Exactly. So I am correct.

I point out that you need an Iz of ≥ 20A, and that that involves considering installation method and all the other applicable rating factors (of which Cf is only one), and you say that.

I'm not sure what you think I've shown you to be correct about, but it certainly isn't your basic premise that 433.1.204 is still written for 3036 fuses.

It isn't, it's written for ring final circuits wired using cables with an Iz of ≥ 20A, i.e. cables with a CCC that takes into account installation method and Ca, Cc, Cd, Cf, Cg, Ci, & Cs.

Yes.

Exhibit B: Table 52.3. Sometimes the regulations impose a minimum csa.

Although for 32A MCBs shouldn't it be a CCC of (32*66.7%) 21.33A?

No, it should be 20A, because that is what has been required for the last 16 years.

I think I have - logic.

 

[EFLImpudence]

I am finding it difficult to debate matters with you.

As with the thread yesterday, you seem to reject every point I make and support that rejection with an explanation which confirms what I am proposing.

 

[ban-all-sheds]

Your proposition is "regulation 433.1.204 is still written for 3036 fuses".

I've repeatedly said that it is not, and I have written nothing which confirms that it is.

It's written for ring circuits where Iz < In. The minimum Iz of 20A may be the Iz for a combination of Method C and a 3036 (just), but it also allows for Method A, 100# and 102# on MCBs.

A ring allows a circuit with a larger In than the Iz of the cable would normally support. Whatever the protective device, Iz must be ≥ 20A. It really doesn't matter what the factors are that reduce a cable's CCC - they are what they are, and if they bring Iz down to < 20A you may not use that cable, and if they don't, you may.

Whatever factors apply to given cable installation, you're either going to be above 20A, or below. It so happens that 2.5mm² Method C is OK if you're using 3036s, but Method A would not be. Method A is OK if you're using an MCB. If you want a ring using a 3036 device, and the cable is Method 103# then you'll have to use 10mm².

It lists all acceptable OPDs.

It makes as much sense to say that therefore 433.1.204 is still written for 3036 fuses than it does to say it is still written for any other type of device.

(Cf) applies to all circuits because of the nature of 3036s, not because of the circuit topology.

Iz has to be 20A. It doesn't matter what the type of device is, it has to be 20A. The less onerous requirements of MCBs vs 3036s means that you can use 2.5mm² cable with MCBs when you might not with fuses due to installation method.

It's no different from any circuit where you need a given Iz - if your device is a 3036 fuse then sometimes you'll need a larger cable than you would if it were an MCB.

I point out that you need an Iz of ≥ 20A, and that that involves considering installation method and all the other applicable rating factors (of which Cf is only one), and you say that.

I'm not sure what you think I've shown you to be correct about, but it certainly isn't your basic premise that 433.1.204 is still written for 3036 fuses.

It isn't, it's written for ring final circuits wired using cables with an Iz of ≥ 20A, i.e. cables with a CCC that takes into account installation method and Ca, Cc, Cd, Cf, Cg, Ci, & Cs.

433.1.204 is not "written for 3036 fuses". It is written for protective devices complying with BS 88 series, BS 3036, BS EN 60898, BS EN 60947-2 or BS EN 61009-1.