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

 

[nicebutdim]

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.

Pete and Dave would apply rating factors and would likely have a decent amount of common sense, whereas I'm enquiring from the position of someone trying to increase their understanding.

One thing I don't get is the idea of 16A circuits being a means of future proofing - while appliances have (and will) become more efficient, it's also likely that they will continue to become more numerous in homes. Surely a better way of future proofing would be to continue to provide a 20A (or higher) supply to those sockets, but using installation methods that are compatible with the sort of insulation you envisage. Downrating the supply sounds more like keeping costs down than future proofing.

 

[davesparks]

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

Please explain how you factor common sense in to the calculations then? How to you translate common sense in to a numerical value to be used in calculations?

I am fully in support of the use of common sense where needed, and mourn its demise. But I don't see how it factors in to a calculation. Unless you mean you just arbitrarily adjust the cable size without calculation?

 

[Mike Johnson]

France and Germany do not run washing machines, dish washers, tumble dryers, water heaters off a radial circuit, but on their own dedicated supply, lots of other appliances have their own dedicated supply as well, so the potential of overloading the socket supply is reduced.

 

[LastManOnline]

Pete and Dave would apply rating factors and would likely have a decent amount of common sense, whereas I'm enquiring from the position of someone trying to increase their understanding.

One thing I don't get is the idea of 16A circuits being a means of future proofing - while appliances have (and will) become more efficient, it's also likely that they will continue to become more numerous in homes. Surely a better way of future proofing would be to continue to provide a 20A (or higher) supply to those sockets, but using installation methods that are compatible with the sort of insulation you envisage. Downrating the supply sounds more like keeping costs down than future proofing.

Pete and dave are clearly scrupulous in their application of regs etc. End of. However, regs must always be seen as a minimum standard. If possible, it's best to be ahead of the curve rather than behind it..We decided to downgrade to a 16 amp mcb for a number reasons. One, as you mentioned appliances are becoming increasingly more efficient. Seven or 8 years ago we either ran a 6mm to the utility to allow washing machine and drier etc to run simultaneously or 2 x 2.5 t& e, depending on the rating of appliances. In the most recent kitchen we did, the entire load of W. M. and Drier was 3.3 KW. That trend will almost certainly continue. General sockets circuits are no longer used for electric heating like they used to be. Down rating the supply does, nt save us any money but it dies "future proof" the installation regarding the installation of more insulation (which is the norm here).
Your point about the increase of appliances, is a valid one. The solution is also simple.As standard we always run in an extra 2.5. to utility/kitchen. Future proofing.

 

[pc1966]

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.

My comment was not directed at you, just an observation about how often the ring/radial topic comes up and how divisive it appears 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.

No, they were deliberately created together.

The UK used to have two common plugs, rated at 5A and 15A (and a further two uncommon at 2A and 30A) , each on a radial circuit. This is wasteful of wiring for a large number of plugs, and inevitably you will end up with the wrong one for your application.

So the IEE (as the IET was then) came up with a proposal post-WW2 to keep costs down, safety up, and allow a large number of sockets as they foresaw the growing need for electrical power.

Hence the idea of a "universal" plug for most applications, but with a selectable fuse rated for the appliance. Today you can get that easily in 3A, 5A and 13A but from suppliers like RS also 1A, 2A, 7A and 10A. With such a fuse you don't care (within reason) what the supplying feed is rated at, so the committee finally settled for a typical 30A fuse behind this (also ensuring total selectivity with a 13A fuse in the event of a fault).

Of course the modern 32A B-curve MCB fails on selectivity but that is a topic for another day (see many posts on garage/out-building supplies)!

The rest of the world does not need them and its very convenient that way.

It is convenient, but wasteful.

The lack of a fused plug means the appliance cable has to meet the disconnection ratings of the main supply. For a typical MCB in the 10-20A range the adiabatic limit requires 1mm cable. So even for a small power demand you are wasting copper simply to meet the supply characteristics instead of, say, 0.5mm and a 3A fuse.

And as you can't sensibly push this supply up due to the final flex issue, you might need several circuits instead of the one ring.

Yes, it works perfectly well and most EU countries, etc, are quite safe, but it is a waste of the Earth's resources in doing so!

 

[LastManOnline]

Please explain how you factor common sense in to the calculations then? How to you translate common sense in to a numerical value to be used in calculations?

I am fully in support of the use of common sense where needed, and mourn its demise. But I don't see how it factors in to a calculation. Unless you mean you just arbitrarily adjust the cable size without calculation?

That's is a question I would love to have an answer for but I don't. It's a great idea.. a numerical value for common sense. My last post to "nicebutdim" is perhaps an example of the application of common sense. I cannot supply a numerical value, but perhaps a definition "factoring in the likely direction of the society we live in". In mine the focus on improved insulation in the home is very clear. The implication for electrical circuits is thus also very clear. So what is the wisest course of action..... Hence the 16amp.socket circuit.
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France and Germany do not run washing machines, dish washers, tumble dryers, water heaters off a radial circuit, but on their own dedicated supply, lots of other appliances have their own dedicated supply as well, so the potential of overloading the socket supply is reduced.

Correct, strictly speaking it's recommended that any circuit over 1500 watt should be on its own circuit

 

[davesparks]

r. The implication for electrical circuits is thus also very clear. So what is the wisest course of action..... Hence the 16amp.socket circuit.

How is that the wisest course of action? Limiting socket circuits to 16A does not seem like a sensible plan.
If you had said you calculate cable size as if there was more insulation than there actually is I could understand it. But to make an arbitrary decision to put all socket circuits on 16A OCPDs seems daft to me.

What size cable do you use for the 16A socket circuits usually?

Do you make the circuits smaller and run more of them to compensate for the reduction in available current?

 

[LastManOnline]

My comment was not directed at you, just an observation about how often the ring/radial topic comes up and how divisive it appears to be.


No, they were deliberately created together.

The UK used to have two common plugs, rated at 5A and 15A (and a further two uncommon at 2A and 30A) , each on a radial circuit. This is wasteful of wiring for a large number of plugs, and inevitably you will end up with the wrong one for your application.

So the IEE (as the IET was then) came up with a proposal post-WW2 to keep costs down, safety up, and allow a large number of sockets as they foresaw the growing need for electrical power.

Hence the idea of a "universal" plug for most applications, but with a selectable fuse rated for the appliance. Today you can get that easily in 3A, 5A and 13A but from suppliers like RS also 1A, 2A, 7A and 10A. With such a fuse you don't care (within reason) what the supplying feed is rated at, so the committee finally settled for a typical 30A fuse behind this (also ensuring total selectivity with a 13A fuse in the event of a fault).

Of course the modern 32A B-curve MCB fails on selectivity but that is a topic for another day (see many posts on garage/out-building supplies)!


It is convenient, but wasteful.

The lack of a fused plug means the appliance cable has to meet the disconnection ratings of the main supply. For a typical MCB in the 10-20A range the adiabatic limit requires 1mm cable. So even for a small power demand you are wasting copper simply to meet the supply characteristics instead of, say, 0.5mm and a 3A fuse.

And as you can't sensibly push this supply up due to the final flex issue, you might need several circuits instead of the one ring.

Yes, it works perfectly well and most EU countries, etc, are quite safe, but it is a waste of the Earth's resources in doing so!

Yes, they were created together. But they belong together as they are interdependent.

 

[davesparks]

Your point about the increase of appliances, is a valid one. The solution is also simple.As standard we always run in an extra 2.5. to utility/kitchen. Future proofing.

What do you do with the extra 2.5?
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Yes, they were created together. But they belong together as they are interdependent.

They are not interdependent, the fused plug is not dependant on a ring circuit.

 

[LastManOnline]

My comment was not directed at you, just an observation about how often the ring/radial topic comes up and how divisive it appears to be.


No, they were deliberately created together.

The UK used to have two common plugs, rated at 5A and 15A (and a further two uncommon at 2A and 30A) , each on a radial circuit. This is wasteful of wiring for a large number of plugs, and inevitably you will end up with the wrong one for your application.

So the IEE (as the IET was then) came up with a proposal post-WW2 to keep costs down, safety up, and allow a large number of sockets as they foresaw the growing need for electrical power.

Hence the idea of a "universal" plug for most applications, but with a selectable fuse rated for the appliance. Today you can get that easily in 3A, 5A and 13A but from suppliers like RS also 1A, 2A, 7A and 10A. With such a fuse you don't care (within reason) what the supplying feed is rated at, so the committee finally settled for a typical 30A fuse behind this (also ensuring total selectivity with a 13A fuse in the event of a fault).

Of course the modern 32A B-curve MCB fails on selectivity but that is a topic for another day (see many posts on garage/out-building supplies)!


It is convenient, but wasteful.

The lack of a fused plug means the appliance cable has to meet the disconnection ratings of the main supply. For a typical MCB in the 10-20A range the adiabatic limit requires 1mm cable. So even for a small power demand you are wasting copper simply to meet the supply characteristics instead of, say, 0.5mm and a 3A fuse.

And as you can't sensibly push this supply up due to the final flex issue, you might need several circuits instead of the one ring.

Yes, it works perfectly well and most EU countries, etc, are quite safe, but it is a waste of the Earth's resources in doing so!

Pc1966. If you were to stand in a room of (for arguments sake) Dutch electricians and present your argument as you have to me they would listen to you, realised you knew exactly what you were talking about, respected your point of view re. waiting earth's resources etc but would not be "converted" to the ring circuit. They don't have fused outlets or fused plugtops and it really is more convenient that way. They are happy to pay a little more (as, you see it) for that convenience. If you worked in their system for a little while you would feel the same.
On the other hand if a Dutch spark came to the UK he would quickly realise that polarity at sockets is a "great idea". And the sockets switches etc are much more robust than he is used to. Swings and roundabouts
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What do you do with the extra 2.5?
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They are not interdependent, the fused plug is not dependant on a ring circuit.

The extra 2.5 we run in for, as "nicebutdim" said the likely possibility of increasing appliances in the future.

Interdependent was the wrong choice of word. I meant to imply that a fused plugtops was inevitable if you have a 32 amp breaker/fuse

 

[davesparks]

The extra 2.5 we run in for, as "nicebutdim" said the likely possibility of increasing appliances in the future.

But what do you actually do with it? Do you leave it unteeminated somewhere or what?

 

[pc1966]

@Edmond Noonan The UK's post-WW2 situation was unusual as so much reconstruction was needed and not that many places actually had electricity outside of major conurbations, and so changing systems in use was practical and advantageous at that point. No one now is going to change the plug/socket type in use due to the massive headache it would cause! (I remember it was still common to see the round-pin outlets in to the 70s)

So really the ring/radial debate is limited to the UK and countries with a shared electrical background where both types are possible.

I remember many years ago there was some discussion about the goal of an common EU-wide electrical socket. Which as you can see got nowhere. What was the most promising choice was the IEC "kettle" style of connector as it is polarised, in widespread use already, and available at 10A (but often only 5A!) so probably enough for the majority of applications.

But then you get in to the details of local fuse/switch or not, and even the issue of shutters. The IEE was not willing to have open sockets and other standard bodies were not bothered as they never had shutters to keep kids from poking stuff in, etc.

 

[nicebutdim]

Pete and dave are clearly scrupulous in their application of regs etc. End of. However, regs must always be seen as a minimum standard. If possible, it's best to be ahead of the curve rather than behind it..We decided to downgrade to a 16 amp mcb for a number reasons. One, as you mentioned appliances are becoming increasingly more efficient. Seven or 8 years ago we either ran a 6mm to the utility to allow washing machine and drier etc to run simultaneously or 2 x 2.5 t& e, depending on the rating of appliances. In the most recent kitchen we did, the entire load of W. M. and Drier was 3.3 KW. That trend will almost certainly continue. General sockets circuits are no longer used for electric heating like they used to be. Down rating the supply does, nt save us any money but it dies "future proof" the installation regarding the installation of more insulation (which is the norm here).
Your point about the increase of appliances, is a valid one. The solution is also simple.As standard we always run in an extra 2.5. to utility/kitchen. Future proofing.

I get your thinking, but remain unconvinced that derating from 20A to 16A in this way is a great means of future proofing. If I was building a new home I'd much rather have more current available at outlets than less - while it may not ever be required, it would surely be advantageous to have it readily available.

On the subject of running in additional circuits; I'm not generally in favour of the idea, unless they are intended for a specific requirement that is to be commissioned in the near future. In my parent's house, the only non-bodged electrical work since the initial introduction of electricity also included the installation of two additional rings and one lighting radial. That was 30 years ago and I wouldn't want to use any of it after three decades of being coiled up in a floor space, with intermittent rodent activity. I mention these additional circuits as I happened upon them a couple of years back - two were cut out and one was left in situ as it could be useful for pulling new cables in the future. In short, those additional circuits weren't a particularly great use of money or cable.

 

[LastManOnline]

But what do you actually do with it? Do you leave it unteeminated somewhere or what?

Yes. Unterminated and taped off in a JB, but obviously accessible. The utility is the location of choice.

 

[nicebutdim]

I remember many years ago there was some discussion about the goal of an common EU-wide electrical socket. Which as you can see got nowhere. What was the most promising choice was the IEC "kettle" style of connector as it is polarised, in widespread use already, and available at 10A (but often only 5A!) so probably enough for the majority of applications.

I wonder if they planned on naming it "The Esperanto"?

 

[LastManOnline]

I get your thinking, but remain unconvinced that dropping derating from 20A to 16A in this way is a great means of future proofing. If I was building a new home I'd much rather have more current available at outlets than less - while it may not ever be required, it would surely be advantageous to have it readily available.

On the subject of running in additional circuits; I'm not generally in favour of the idea, unless they are intended for a specific requirement that is to be commissioned in the near future. In my parent's house, the only non-bodged electrical work since the initial introduction of electricity also included the installation of two additional rings and one lighting radial. That was 30 years ago and I wouldn't want to use any of it after three decades of being coiled up in a floor space, with intermittent rodent activity. I mention these additional circuits as I happened upon them a couple of years back - two were cut out and one was left in situ as it could be useful for pulling new cables in the future. In short, those additional circuits weren't a particularly great use of money or cable.

Planning for the future is not an exact science. You may for instance never put in garden lights but running an SWA to the garden while the house is been built is much cheaper, more convenient and ascetically far more pleasing than doing it at a later stage. But these are all personal decisions where the homeowner is given the option. If they like gfine, if not, fine. We provide a, service at the end of the day.

Regarding the 2 5 t&e, its continuous current rating when covered in insulation drops to 19.5 amps. If installed in wavin it drops to 18.5 amps

I get your thinking, but remain unconvinced that derating from 20A to 16A in this way is a great means of future proofing. If I was building a new home I'd much rather have more current available at outlets than less - while it may not ever be required, it would surely be advantageous to have it readily available.

On the subject of running in additional circuits; I'm not generally in favour of the idea, unless they are intended for a specific requirement that is to be commissioned in the near future. In my parent's house, the only non-bodged electrical work since the initial introduction of electricity also included the installation of two additional rings and one lighting radial. That was 30 years ago and I wouldn't want to use any of it after three decades of being coiled up in a floor space, with intermittent rodent activity. I mention these additional circuits as I happened upon them a couple of years back - two were cut out and one was left in situ as it could be useful for pulling new cables in the future. In short, those additional circuits weren't a particularly great use of money or cable.

Planning for future needs is not an exact science of course. Sometimes it running in an extra, cable can be good insurance but as you state it can also be wasted. It's a choice at the end of the day.

Regarding from 20 to 16amp circuits. You will see from the table that their is a significant difference in current carrying capacity between a surface clipped 2.5 and one embedded in insulation. Approx 8 amps. In fact the rating of a 2.5 t&e in insulation is 19.5 amps, thus under 20amps.Though marginal, this figure may still require other derating factors (like wavin pipe, 18.5 amps) and bunching (derating factor is 0.80), which is often inevitable in an attic.You can see why we feel much more comfortable with a 16amp mcb in installations likely to be insulated
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Planning for the future is not an exact science. You may for instance never put in garden lights but running an SWA to the garden while the house is been built is much cheaper, more convenient and ascetically far more pleasing than doing it at a later stage. But these are all personal decisions where the homeowner is given the option. If they like gfine, if not, fine. We provide a, service at the end of the day.

Regarding the 2 5 t&e, its continuous current rating when covered in insulation drops to 19.5 amps. If installed in wavin it drops to 18.5 amps

Planning for future needs is not an exact science of course. Sometimes it running in an extra, cable can be good insurance but as you state it can also be wasted. It's a choice at the end of the day.

Regarding from 20 to 16amp circuits. You will see from the table that their is a significant difference in current carrying capacity between a surface clipped 2.5 and one embedded in insulation. Approx 8 amps. In fact the rating of a 2.5 t&e in insulation is 19.5 amps, thus under 20amps.Though marginal, this figure may still require other derating factors (like wavin pipe, 18.5 amps) and bunching (derating factor is 0.80), which is often inevitable in an attic.You can see why we feel much more comfortable with a 16amp mcb in installations likely to be insulated

Sorry for confusion. Thought I lost my first post, then it reappeared
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@Edmond Noonan The UK's post-WW2 situation was unusual as so much reconstruction was needed and not that many places actually had electricity outside of major conurbations, and so changing systems in use was practical and advantageous at that point. No one now is going to change the plug/socket type in use due to the massive headache it would cause! (I remember it was still common to see the round-pin outlets in to the 70s)

So really the ring/radial debate is limited to the UK and countries with a shared electrical background where both types are possible.

I remember many years ago there was some discussion about the goal of an common EU-wide electrical socket. Which as you can see got nowhere. What was the most promising choice was the IEC "kettle" style of connector as it is polarised, in widespread use already, and available at 10A (but often only 5A!) so probably enough for the majority of applications.

But then you get in to the details of local fuse/switch or not, and even the issue of shutters. The IEE was not willing to have open sockets and other standard bodies were not bothered as they never had shutters to keep kids from poking stuff in, etc.

Yes. Its often just history, is, nt it. Anyway if debating pro, s and con, s of rings /radials is our biggest problem, we must be in a good place.
Onwards and upwards

 

[nicebutdim]

Sorry, I'd taken your earlier post to mean you ran in additional circuits as standard and not at the customer's request.

I'm in a 3 year old house with all socket circuits wired as rings. I'd have been happy enough with 20A radials upstairs and also downstairs, with the exception of kitchen and utility, but that discussion never took place. If the option had been put to me and those radials were to have been 16A, I'd have requested 32A rings or 20A radials run in 4mm at a relatively small additional cost. Chances are that 16A would be sufficient for our needs (outside of kitchen and utility), but I'd rather know that additional capacity was available.

A few years ago our eldest bought himself a 2kW fan heater for his bedroom, because he's special and needs to look after himself better than the rest of us I've no idea how long he had that heater, but can tell you that he didn't have it for long after I discovered it. Now I've no idea of the power factor of such heaters, nor that of most domestic appliances, but even in the best scenario that heater and a vacuum cleaner running on the same circuit must get close to tripping a 16A breaker.

 

[Risteard]

That's fine Risteard. Do you also still "support and endorse" the installation of a 4ft earth rod (as we are both required to install under Irish regs) but as has been demonstrated here on this forum by multiple sparks in multiple posts is actually less than useless?

Yes I do, and as you rightly state essentially I have no choice. I myself have pointed out how a very low impedance would be required in many circumstances (depending on the load) to limit the touch voltage to a safe level. However I still believe that an Earth electrode is better than no Earth electrode. I honestly feel that the IEE Wiring Regulations are at odds with the rest of the world on this, and there is a reasonable probability that they will change in due course.

But yes - we should ideally be striving for a much lower impedance connection, although this could mean substantially more work to achieve this.

 

[pc1966]

Yes. Its often just history, isnt it. Anyway if debating pro, s and con, s of rings /radials is our biggest problem, we must be in a good place.
Onwards and upwards

As they say "First world problem"

 

[LastManOnline]

Yes I do, and as you rightly state essentially I have no choice. I myself have pointed out how a very low impedance would be required in many circumstances (depending on the load) to limit the touch voltage to a safe level. However I still believe that an Earth electrode is better than no Earth electrode. I honestly feel that the IEE Wiring Regulations are at odds with the rest of the world on this, and there is a reasonable probability that they will change in due course.

But yes - we should ideally be striving for a much lower impedance connection, although this could mean substantially more work to achieve this.

Yes. You made the valid point about the need for a very low impedence in a previous point. Agreed. That's, essential. But before we would recommend to other countries (UK for example) that they should install a 4ft rod can we explain clearly to them why? Its, been clearly established mathematically (here on this forum) that a 4ft rod is of no use as a, return path in the event of a broken neutral. Secondly, its been argued (mathematically) that the rod does, nt bring down the touch voltage during fault conditions. I would go one step further and argue (mathematically) that a 4ft rod will actually be a potential safety hazard under fault conditions. I would be happy (even reassured) to be proved wrong in that assumption

 

[Mike Johnson]

Hmm my French house has a TT supply and a 3M rod, resistance value is 56Ω should I panic now?

 

[LastManOnline]

Hmm my French house has a TT supply and a 3M rod, resistance value is 56Ω should I panic now?

No absolutely not. The issue is actually with TNC-S and the widespread (but erroneous belief) that the rod plays the same role in this supply system as it dies in a TT system. By the way a res of 56 ohms?? That's a dream come true over here
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No absolutely not. The issue is actually with TNC-S and the widespread (but erroneous belief) that the rod plays the same role in this supply system as it dies in a TT system. By the way a res of 56 ohms?? That's a dream come true over here☺

Did you test that rod isolated from other earth's?

 

[davesparks]

Yes. Unterminated and taped off in a JB, but obviously accessible. The utility is the location of choice.

So in the future, if it is needed as the customer has bought a new appliance and overloaded the 16A circuit you installed, they have to call you back to connect this other cable and make more current available?

That sounds like a terrible installation design to me, and I'm sure the customers will agree

 

[Mike Johnson]

Did you test that rod isolated from other earth's?

This is on the outside of most rural properties in France for exactly that purpose.

 

[LastManOnline]

So in the future, if it is needed as the customer has bought a new appliance and overloaded the 16A circuit you installed, they have to call you back to connect this other cable and make more current available?

That sounds like a terrible installation design to me, and I'm sure the customers will agree

How is that the wisest course of action? Limiting socket circuits to 16A does not seem like a sensible plan.
If you had said you calculate cable size as if there was more insulation than there actually is I could understand it. But to make an arbitrary decision to put all socket circuits on 16A OCPDs seems daft to me.

What size cable do you use for the 16A socket circuits usually?

Do you make the circuits smaller and run more of them to compensate for the reduction in available current?

Yes. Simple run in more circuits. Not complicated. You will find most continental countries have their socket Circuits at 16 amps. Appliances generally have their own curcuits.

DAVE SPARKS "if you had said you calculate cable size as if there is more insulation..". That's exactly what I said. The decision was, spe ifically made in relation increasing insulation. Reread my post.
I use 2.5 t&e for socket circuits.

Now, an exercise. Check the tables for current carrying capacity of a 2.5 t&e in insulation. Use the appropriate derating factors and see if you are still comfortable using a 20amp mcb?

By the way how many appliances, in your home will trip a 16 amp mcb.

Lastly, no decisions are set in stone. We play what's in front of, but always erring on the side of caution.

 

[davesparks]

Now, an exercise. Check the tables for current carrying capacity of a 2.5 t&e in insulation. Use the appropriate derating factors and see if you are still comfortable using a 20amp mcb?

By the way how many appliances, in your home will trip a 16 amp mcb.

That is a ridiculous exercise as it does not follow the rules for calculating cable size.
You apply rating factors to the nominal current and then select a cable size based on that calculation.

Your 'exercise' suggests starting with a cable size and working backwards to a nominal current, this is incorrect.

I am well aware that a 20A circuit wired in T&E through insulation will require a minimum of 4.0mm, but that is irrelevant to the point.

On their own i don't think any appliance with a plug will trip a 16A MCB unless faulty. However a combination of 2 or more on the same circuit will trip a 16A MCB quite easily.

 

[Mike Johnson]

Yes. Simple run in more circuits. Not complicated. You will find most continental countries have their socket Circuits at 16 amps. Appliances generally have their own circuits.

Ah ha Edmond you have been listening.

 

[davesparks]

Yes. Simple run in more circuits. Not complicated. You will find most continental countries have their socket Circuits at 16 amps. Appliances generally have their own curcuits.

I use 2.5 t&e for socket circuits.

I am aware that most continental European countries have their socket circuits on 16A MCB's, and they run more circuits than we normally would. That is largely irrelevant as they are following their regulations and standard practices, we follow our regulations.
Most continental countries drive in the other side of the road and use Km instead of miles, that does not mean we need to change to match them.

Surely you use the cable size selected as a result of the standard calculations, stating that you use 2.5 for socket circuits is daft.

 

[nicebutdim]

Now, an exercise. Check the tables for current carrying capacity of a 2.5 t&e in insulation. Use the appropriate derating factors and see if you are still comfortable using a 20amp mcb?

Do you, like most of continental Europe, run dedicated circuits for fixed appliances or are such appliances running on a single 16A circuit? Your earlier washer/dryer comment led me to believe those appliance are not on dedicated circuits, but on the same 16A circuit as other appliances.

While I like the idea of an electrician wiring homes to take future additional insulation into account, I can't help thinking that I'd prefer that to take the form of more robust infrastructure, rather than less available current.

What way do you run kitchen sockets? I'm inclined to think that these may be 20A radials in 4mm as 6mm would be a bit impractical for installation, but kitchens attract all manner of gadgets, several of which could be running at the same time.

 

[LastManOnline]

That is a ridiculous exercise as it does not follow the rules for calculating cable size.
You apply rating factors to the nominal current and then select a cable size based on that calculation.

Your 'exercise' suggests starting with a cable size and working backwards to a nominal current, this is incorrect.

I am well aware that a 20A circuit wired in T&E through insulation will require a minimum of 4.0mm, but that is irrelevant to the point.

On their own i don't think any appliance with a plug will trip a 16A MCB unless faulty. However a combination of 2 or more on the same circuit will trip a 16A MCB quite easily.

If I had chosen to wire the socket circuits in this particular install in 4mm to SUIT 20 amp MCB's I would be guilty of poor design and wastefulness and cause unneeded expense for the home owner. His 2 heaviest appliances are 1800 and 1500 watts. He has access to 4 separate circuits in his kitchen. I can confidently predict he will enjoy years of hassle free cooking, hoovering etc.

 

[nicebutdim]

Most continental countries drive in the other side of the road and use Km instead of miles, that does not mean we need to change to match them.

ROI did change to KM several years back.

What I'm trying to grasp is whether these installations are going down the route of multiple circuits, where the UK might use one, and the use of much larger CUs to accomodate many extra ways. If that's the case then I can understand lower rated circuits.

 

[davesparks]

If I had chosen to wire the socket circuits in this particular install in 4mm to SUIT 20 amp MCB's I would be guilty of poor design and wastefulness and cause unneeded expense for the home owner. His 2 heaviest appliances are 1800 and 1500 watts. He has access to 4 separate circuits in his kitchen. I can confidently predict he will enjoy years of hassle free cooking, hoovering etc.

4 circuits for the kitchen is wasteful and unneeded expense. It uses more cable and 4x RCBO instead of 1.
One ring circuit is normally adequate for the ground floor of the average house.

With your 16A radial approach how big do your CUs and DBs end up being?

 

[LastManOnline]

I am aware that most continental European countries have their socket circuits on 16A MCB's, and they run more circuits than we normally would. That is largely irrelevant as they are following their regulations and standard practices, we follow our regulations.
Most continental countries drive in the other side of the road and use Km instead of miles, that does not mean we need to change to match them.

Surely you use the cable size selected as a result of the standard calculations, stating that you use 2.5 for socket circuits is daft.

My "" stating that I use 2.5 for socket circuits is daft"" is, pardon me, daft. Worldwide 2.5 is used for socket circuits. For general socket circuits, we don't need to make "standard calculation", we need to ensure that the cable is protected properly under whatever conditions it's been installed.Simple as. That is in my experience how socket cir uits are wired worldwide. Now when it comes to fixed appiances etc, we naturally begin with the load first and work back.

As, regards "this is what the Europeans do and this is what we do" is a mantra I don't support. I much prefer, let's see what "they do" (whoever they may be) and what we can learn from them. They and you (UK) do a number of things we (Eire) can learn from. I As, you have probably gathered I am all for change (positive change that is). I see it as "win, win"
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Do you, like most of continental Europe, run dedicated circuits for fixed appliances or are such appliances running on a single 16A circuit? Your earlier washer/dryer comment led me to believe those appliance are not on dedicated circuits, but on the same 16A circuit as other appliances.

While I like the idea of an electrician wiring homes to take future additional insulation into account, I can't help thinking that I'd prefer that to take the form of more robust infrastructure, rather than less available current.

What way do you run kitchen sockets? I'm inclined to think that these may be 20A radials in 4mm as 6mm would be a bit impractical for installation, but kitchens attract all manner of gadgets, several of which could be running at the same time.

Yes. Any load above 1500 watts is recommended to have its own circuit.

 

[nicebutdim]

Yes. Any load above 1500 watts is recommended to have its own circuit.

What about kitchen sockets?

 

[LastManOnline]

What about kitchen sockets?

It's a minimum of 2 circuits. But the key reminder we have gotten here for many years is"the regs are a MINIMUM""requirement.

 

[nicebutdim]

It's a minimum of 2 circuits. But the key reminder we have gotten here for many years is"the regs are a MINIMUM""requirement.

2x20A or 2x 16A?

It's this room, where a plethora of gadgets that draw significant current can usually be found. Would be difficult to guess where a homeowner might plug their kettle and toaster in, when deciding which circuit to power a built in microwave from.

I don't dislike your thinking, but I'm not quite over the line in sharing it. As a homeowner (not an electrician) I'd much rather see a 32A supply for kitchen sockets, regardless of whether that takes the form of a ring or radial. For 364 days of the year I think your ideas would be fine for our household, but I wouldn't want to guide the other half and kids toward specific sockets for that other 1 or 2 days each year when they go mad with baking or whatever else that range of gadgets are used for.

Looking around our modest sized kitchen I see 3 circuits: Oven/hob, fridge freezer and general sockets, of which there are 10 (5x 2g). Splitting those sockets over two circuits would be difficult as there can be appliances that draw considerable current plugged into any of them, although most loads are admittedly very light.

 

[Mike Johnson]

A typical three phase Domestic circuit board in the EU, in fact France, but could be Germany, Norway........................

 

[nicebutdim]

A typical three phase Domestic circuit board in the EU, in fact France, but could be Germany, Norway........................

That's what I was driving at in a previous post - whether this sort of board is being used in Ireland if circuits are run in greater numbers at lower ratings.

 

[LastManOnline]

2x20A or 2x 16A?

It's this room, where a plethora of gadgets that draw significant current can usually be found. Would be difficult to guess where a homeowner might plug their kettle and toaster in, when deciding which circuit to power a built in microwave from.

I don't dislike your thinking, but I'm not quite over the line in sharing it. As a homeowner (not an electrician) I'd much rather see a 32A supply for kitchen sockets, regardless of whether that takes the form of a ring or radial. For 364 days of the year I think your ideas would be fine for our household, but I wouldn't want to guide the other half and kids toward specific sockets for that other 1 or 2 days each year when they go mad with baking or whatever else that range of gadgets are used for.

Looking around our modest sized kitchen I see 3 circuits: Oven/hob, fridge freezer and general sockets, of which there are 10 (5x 2g). Splitting those sockets over two circuits would be difficult as there can be appliances that draw considerable current plugged into any of them, although most loads are admittedly very light.

2 x 20 amps would be the norm. Installing 16 amp mcb, s is not the norm here. Remember I stated this is my first time applying this measure. But I think it will become more common in the future.
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That's what I was driving at in a previous post - whether this sort of board is being used in Ireland if circuits are run in greater numbers at lower ratings.

Very unlikely 3 phase boards will be used here.
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A typical three phase Domestic circuit board in the EU, in fact France, but could be Germany, Norway........................View attachment 59939

Yes. You can add Sweden to that list. 3 phase in domestic situations is in my view a positive developement

 

[nicebutdim]

Very unlikely 3 phase boards will be used here.

I was going to edit that post, but figured you get that I was referring to the use of boards with significant capacity and not 3 phase installations.
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2 x 20 amps would be the norm. Installing 16 amp mcb, s is not the norm here. Remember I stated this is my first time applying this measure. But I think it will become more common in the future.

I'm very much in favour of breaking with convention, when doing so fulfills a need or improves upon convention - whether that be a one off circumstance or in a more widespread manner.

What I struggle with here are the potential limitations placed upon homeowners as that house could have new occupants 2 or 3 years from now, with very different requirements to the current occupant. It may be that you have got this installation bang on the money for the style of property, but I can only consider the issue from my own perspective and limited experiences. Your ideas may not meet with universal approval, but I like that they challenge convention and give me something to think about.