4mm radial circuit

[marshr02]

Yeah, why didn't I think of that, read replies that had not yet been written :dizzy2:

You should be a politician, answering one question with one of your own. LOL

I really want to believe that there is no method B for T/E - hence if not insulation then it's method C. BUT the OSG references it - page 52 Table 7.2.

 

[Richard Burns]

The standard circuit A2 in the OSG does mention that the csa of the cables has to be assessed for CCC based on the installation method and the "informative" radial final circuit in the appendix of BS7671 also says that over current protection is not considered.

Because this is such a common circuit, it may well be installed incorrectly fairly often, but one can consider that domestic circuits almost never trip on overload and the likely current being carried will be far less than 30A so there is no significant danger, although as you say it will not meet the requirements of the regulations in many cases.

(copied my reply from the reference method explained thread)

 

[marshr02]

The standard circuit A2 in the OSG does mention that the csa of the cables has to be assessed for CCC based on the installation method and the "informative" radial final circuit in the appendix of BS7671 also says that over current protection is not considered.

Because this is such a common circuit, it may well be installed incorrectly fairly often, but one can consider that domestic circuits almost never trip on overload and the likely current being carried will be far less than 30A so there is no significant danger, although as you say it will not meet the requirements of the regulations in many cases.

(copied my reply from the reference method explained thread)

Thanks for the reply. Yes, your info is what I've read - I guess I really want the BS7671 & OSG to 'make sense'. In this case there seems to be a hole. Ref B, I understand includes cables under the floor (in a building void, BS7671). So even if you remove ALL conduit, almost ALL domestic installations will involve cables under the floor - ref B. Hence the OSG A2 cct recommended for domestic installations must implicitly assume ref B (@30A) is JUST okay. The frustrating thing is the regs don't come out and say this - which is the sort of leadership I hoped the IET would provide.

 

[Richard Burns]

The frustrating thing is the regs don't come out and say this - which is the sort of leadership I hoped the IET would provide.

This is a vain hope indeed!!!:nonod:
With all the verbiage coming from the IET you would expect clarity but it is never there, always grey.

 

[Tuttle]

Why don't you just use 6mm if you are concerned about it (that's what I'd do)?

 

[marshr02]

Why don't you just use 6mm if you are concerned about it (that's what I'd do)?

Because I'm not discussing what to do about a ONE off job. I'm discussing a flaw with a prescribed cct that is being installed by thousands of electricians across the country for years

 

[marshr02]

I'm coming to the conclusion that if the layout of a house suits radial ccts then 20A, with 2.5mm is more flexible, just likely to be running one more cct. With 32A radial used sparingly, say for the kitchen. (Obviously if the layout suits ring then I would use ring)

 

[kingeri]

I'm coming to the conclusion that if the layout of a house suits radial ccts then 20A, with 2.5mm is more flexible, just likely to be running one more cct. With 32A radial used sparingly, say for the kitchen. (Obviously if the layout suits ring then I would use ring)

Which is exactly what many sparks do these days. 20A radials for bedrooms, living room etc. and (personally) a 32A 2.5mm ring for kitchens, usually installed 'staggered'. I'd much rather work with 2.5mm anyway, much easier to terminate into socket outlets. 32A radials pretty easily fall below 32A CCC depending on installation method, and also because 4mm only has a 1.5mm CPC the circuit length is quite limited by Zs.

 

[marshr02]

Which is exactly what many sparks do these days. 20A radials for bedrooms, living room etc. and (personally) a 32A ring for kitchens, usually installed 'staggered'. I'd much rather work with 2.5mm anyway, much easier to terminate. 32A radials pretty easily fall below 32A CCC depending on installation method, and also because 4mm only has a 1.5mm CPC the circuit length is quite limited by Zs.

Thanks for reply. Just out of interest, would you be happy, putting 4mm in oval conduit into a plastered wall, and clipping to joists, and then running on a 32A CB?

 

[Tuttle]

I'm coming to the conclusion that if the layout of a house suits radial ccts then 20A, with 2.5mm is more flexible, just likely to be running one more cct. With 32A radial used sparingly, say for the kitchen. (Obviously if the layout suits ring then I would use ring)

I thought about using a 4mm 32A radial once and came to the same conclusion as you. It only seems to be good for ref method C and I think there could be a problem fitting three 4mm conductors into accessories if you need to branch off at any point or modify the circuit at a later date, so I used a 2.5mm ring instead.

 

[Sparkytlec]

I usually use 4mm radials for socket but put them on a 20A o/c device and 2.5mm on a 16A. I haven't had a report of them tripping on overload either. It's very unusual for me to use a ring circuit these days to.

 

[marshr02]

I usually use 4mm radials for socket but put them on a 20A o/c device and 2.5mm on a 16A. I haven't had a report of them tripping on overload either. It's very unusual for me to use a ring circuit these days to.

Thanks for reply. Out of interest if you are using a 20A o/c device, why do you run 4.0mm. Is it due to volt drop or sim - as obviously 2.5mm carries 20A on most installation methods...? Cheers

 

[marshr02]

I thought about using a 4mm 32A radial once and came to the same conclusion as you. It only seems to be good for ref method C and I think there could be a problem fitting three 4mm conductors into accessories if you need to branch off at any point or modify the circuit at a later date, so I used a 2.5mm ring instead.

Thanks for reply. I suspect that it would be useful for the IET or similar to perform tests with T/E in installation method B, rather than using the multicore values in BS7671. I suspect the cable is JUST OKAY for 32A - although because it's on the limit I would use it sparingly when layout makes radial more suited in the kitchen. We really could do with one of the professional bodies carrying out the test and issuing a judgement - rather than loads of us wasting time/sleep wondering if we should downrate the CB. Cheers.

 

[Sparkytlec]

Volt drop is one reason in larger cable runs. But I do it that way as it gives me the option to use the o/c to follow the letter of the regs if required, but for my own piece of mind I drop to 20A

 

[Engineer54]

Thanks for reply. I suspect that it would be useful for the IET or similar to perform tests with T/E in installation method B, rather than using the multicore values in BS7671. I suspect the cable is JUST OKAY for 32A - although because it's on the limit I would use it sparingly when layout makes radial more suited in the kitchen. We really could do with one of the professional bodies carrying out the test and issuing a judgement - rather than loads of us wasting time/sleep wondering if we should downrate the CB. Cheers.

Perhaps if you disregarded BS 7671 when it comes to CCC of cables, and use the manufacturers data, you may find that your worries are totally unfounded!!

Why do you and it seems many others, need every situation documented in BS7671 (or by other bodies), it's never going to happen!! BS7671 is basically only a guide at the end of the day, your still expected to make your own educated decisions based on your electrical knowledge etc!!

 

[marshr02]

Perhaps if you disregarded BS 7671 when it comes to CCC of cables, and use the manufacturers data, you may find that your worries are totally unfounded!!

Why do you and it seems many others, need every situation documented in BS7671 (or by other bodies), it's never going to happen!! BS7671 is basically only a guide at the end of the day, your still expected to make your own educated decisions based on your electrical knowledge etc!!

Alright - easy boy.... Thanks for the reply. Purchase my T&E cables over the trade counter - no idea the manufacturer - but will look for any clue - of course I still may have a mix of manufacturers? I will look do some digging for manufacturers info on T&E though - looks interesting - thanks for prodding me in a different direction. Regarding looking to fall back on BS7671 - well the BS regs are a standard - and so if a cable is to say BS6004 then you should expect a certain minimum performance. Any Professional Engineer will tell you that you avoid designing to bespoke products IF possible - a generalised design giving more options at procurement. In this case what I NEED from BS7671 is accurate data on cable performance - to be able to make an informed decision.

 

[Heisenberg]

Perhaps if you disregarded BS 7671 when it comes to CCC of cables, and use the manufacturers data, you may find that your worries are totally unfounded!!

That's a nice try, but aside from the fact that most times data is not available for the cheaper end of the market, even a company like Prysmian only gives CCC based on 2 reference methods. Of which 'B' ain't one of 'em.

And just maybe, people are afraid to step too far from the confines and protection of BS7671 because they know that these days people are quick to sue when things go south. Not everyone has decades of experience to fall back on, so whilst what you said might apply to some, to expect it to be applicable to everyone is unrealistic.

Cheers

 

[Geoffsd]

This is all assuming that 'under the floorboards' is method B.

What does 1.5De ≤ V < 50De mean?

where De is diameter of cable and V is height of space.

I can understand one side or the other but together it doesn't seem to make sense.

 

[Guest55]

Yeah, why didn't I think of that, read replies that had not yet been written :dizzy2:

You should be a politician, answering one question with one of your own. LOL

they were written by the time you read my reply so what difference does it make ?
i should have been a lawyer with my expert arse covering posts.

 

[telectrix]

from troll to lawyer requires at least a 6 day short course. day 1. learning to lie. day 2. learning legal gobbledegook. day 3. learning to lie convincingly. day 4. learning how to backstab. day 5. review of lying abilities. day 6. award of liars (lawyers certificate).