Ring main.

[davesparks]

4MM2 MATE, ,

That is the minimum size allowed but is still subject to calculation.
In a modern house where every void possible is stuffed full of insulation it is likely to affect the calculations and result in 6mm being required.

 

[nicebutdim]

4MM2 MATE, ,

That's what I'd always understood to be the case for a 32A radial, but checked the OSG while typing that previous post and it shows that 4mm would only be suitable when clipped direct - of course I may be reading this incorrectly or failing to take other factors into account...

I'm here to learn from better minds than mine and usually try to find answers from old threads, but sometimes a question arises that I can not reconcile on my own.
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That is the minimum size allowed but is still subject to calculation.
In a modern house where every void possible is stuffed full of insulation it is likely to affect the calculations and result in 6mm being required.

Thanks for this clarification. I've been navigating my way through regulations for a while, but installation methods sometimes cause me to pause and this was one of those instances. The circuit I envisaged was buried an a wall where it dropped to outlets, but clipped direct in the ceiling void - in such instances does the lower rating count or the most prevalent installation method?

 

[davesparks]

Thanks for this clarification. I've been navigating my way through regulations for a while, but installation methods sometimes cause me to pause and this was one of those instances. The circuit I envisaged was buried an a wall where it dropped to outlets, but clipped direct in the ceiling void - in such instances does the lower rating count or the most prevalent installation method?

The most onerous set of conditions that the cable is exposed to is used for the calculations.

Don't forget you can't just read the current rating from the tables, they are intended to be used in conjunction with the rating factors.
Also note that the rating factors can increase as well as decrease the tabulated current carrying capacity.

 

[nicebutdim]

The most onerous set of conditions that the cable is exposed to is used for the calculations.

Don't forget you can't just read the current rating from the tables, they are intended to be used in conjunction with the rating factors.
Also note that the rating factors can increase as well as decrease the tabulated current carrying capacity.

That last sentence is something to bear in mind as I tend to look for limiting factors, rather than those which may improve a situation.

Really need to get started with C&G 2365 as I'm continually setting, and trying to answer, questions that I don't have sufficient understanding to properly resolve - often inspired by real world experiences posted on this forum.

 

[LastManOnline]

I know little of the practices employed in other countries - in fact I have limited knowledge of UK practices and hoover up information where it is available - but had read threads that mentioned some fairly complex radial circuits. These may have been in very old properties and not the sort of circuit conventially installed, but the subject of easier inspection and testing was raised and I thought it a reasonable question to ask.

The radial/ring debate is something of a fascination for me and my untrained mind can see benefits and drawbacks to both. In general I tend to prefer the idea of radial circuits, but can also see instances where a ring seems the more practical option - one example would be a kitchen or utility room that houses multiple power hungry appliances. Even with the application of diversity there is a good chance of washer, dryer, dishwasher and kettle being used at once and potentially overloading a 20A radial, which I guess is why those rooms tend to be fed from a 32A breaker. Unless my understanding of BS 7671:2018 is flawed, a 32A radial, which is buried in plaster (or conduit in plaster) would need to be run in 6mm and not particularly convenient from the perspective of installation?

The"radial /ring debate" is one you will only find discussed in the British Isles in my experience. The rest of the world appears to have drawn its own conclusions. My previous posts have made my own views clear. Seeing the advantages that each wiring method offers is really the way forward.

 

[davesparks]

That last sentence is something to bear in mind as I tend to look for limiting factors, rather than those which may improve a situation.

It's never made clear at college either, they always refer to the rating factors as de-rating factors when in fact they can go either way.

The CCC tables are for ambient temperature of 30C, usually ambient temperature is a bit less in the UK so the rating factor increases the tabulated value.

Further confusion can be had from the way a calculation is normally done, rating factors are usually applied to the nominal current rather than to the tabulated CCCs. This way when a de-rating factor is applied the nominal current is increased.

 

[LastManOnline]

That's what I'd always understood to be the case for a 32A radial, but checked the OSG while typing that previous post and it shows that 4mm would only be suitable when clipped direct - of course I may be reading this incorrectly or failing to take other factors into account...

I'm here to learn from better minds than mine and usually try to find answers from old threads, but sometimes a question arises that I can not reconcile on my own.
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Thanks for this clarification. I've been navigating my way through regulations for a while, but installation methods sometimes cause me to pause and this was one of those instances. The circuit I envisaged was buried an a wall where it dropped to outlets, but clipped direct in the ceiling void - in such instances does the lower rating count or the most prevalent installation method?

Interesting post this because ....
1) Pete 999 is correct
2)you are correct, and
3)Davesparks is correct.

In reality, the rating factors as Davesparks says may go up or down. Then we need to factor in something not mentioned often enough in the regs (for my liking), "common sense". In reality the likely hood is that insulation in houses will become more used as time goes by. We have this year started to use 16 amp mcb, s as standard for general socket circuits to "future proof" current installation work.

 

[pc1966]

The"radial /ring debate" is one you will only find discussed in the British Isles in my experience. The rest of the world appears to have drawn its own conclusions.

But (most of) the rest of the world does not use fused plugs. Hence the advantage of the ring in terms of high number of sockets and loading diversity from many appliances and a supply MCB well above what would safe for the appliance wiring alone don't really apply.

Testing is another long drawn debate as well. The ring final has its own peculiar test strategy as you have both ends to play with (and to verify), but doing so it often a more through test than easily done with a radial set. Also if the radial test is half the time (as Mike suggested) but you have 3 times the number of final circuits you don't gain much!

Both circuits have their places so I don't really get the anti-ring/radial intensity of feelings as usually it comes from not seeing where each is best used.
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In reality, the rating factors as Davesparks says may go up or down.

Just like investments. Usually down!

Obvious one that appears from time to time are 16mm tails on a 100A supply fuse - plenty good enough as they are well ventilated and not bunched in a common sheath so getting the heat out is not like most folk remember for 16mm SWA, etc.

 

[davesparks]

Interesting post this because ....
1) Pete 999 is correct
2)you are correct, and
3)Davesparks is correct.

In reality, the rating factors as Davesparks says may go up or down. Then we need to factor in something not mentioned often enough in the regs (for my liking), "common sense". In reality the likely hood is that insulation in houses will become more used as time goes by. We have this year started to use 16 amp mcb, s as standard for general socket circuits to "future proof" current installation work.

There is no requirement to factor in 'common sense' in cable calculations.
Carry out the calculations correctly and you will get the correct size cable.
You can factor in known future changes, but you cannot factor in unknowns.

You cannot be 'future proof' as the future is unknown, you can only guess at what the future might be.

As for installing only 16A socket circuits, we'll, I suspect my opinion of that idea would get me banned.

 

[LastManOnline]

But (most of) the rest of the world does not use fused plugs. Hence the advantage of the ring in terms of high number of sockets and loading diversity from many appliances and a supply MCB well above what would safe for the appliance wiring alone don't really apply.

Testing is another long drawn debate as well. The ring final has its own peculiar test strategy as you have both ends to play with (and to verify), but doing so it often a more through test than easily done with a radial set. Also if the radial test is half the time (as Mike suggested) but you have 3 times the number of final circuits you don't gain much!

Both circuits have their places so I don't really get the anti-ring/radial intensity of feelings as usually it comes from not seeing where each is best used.
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Just like investments. Usually down!

Obvious one that appears from time to time are 16mm tails on a 100A supply fuse - plenty good enough as they are well ventilated and not bunched in a common sheath so getting the heat out is not like most folk remember for 16mm SWA, etc.

Firstly the "feelings of intensity" I personally don't have. And I hope by some of my language I have, nt inspired them. I actually joined this forum because of the quality of the posts. I noticed the tendency to back arguments up with hard facts and that is where I like to be.
One point I would like to make. The fused plugs are a direct consequence of the ring circuit with its 32 amp OCPD. The rest of the world does not need them and its very convenient that way.

Your comment on the 16mm tails is spot on. I agree comeplelty. I dare not use the phrase "common sense" again as davesparks won't get a wink of sleep?
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There is no requirement to factor in 'common sense' in cable calculations.
Carry out the calculations correctly and you will get the correct size cable.
You can factor in known future changes, but you cannot factor in unknowns.

You cannot be 'future proof' as the future is unknown, you can only guess at what the future might be.

As for installing only 16A socket circuits, we'll, I suspect my opinion of that idea would get me banned.

Regarding the statement, there is "no requirement to factor in common sense". Perhaps not in your world, but there certainly is in mine. You are entitled to your own opinion here dave but as, has oft been said, you not entitled to your own facts. New regulations and requirements tend to appear as individuals use common sense and insight rather than just "follow the regs". You have contributed some significant and educational posts on a number of topics, but the above is not one of your finest