Not just another 'Shed Thread'.
- Thread starter conny
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OK start and end of ring final is at the consumer unit.
I would consider a kitchen ring final to be dedicated to kitchen appliances so would not be included in the appendix 2 kW suggestion.
If we consider the ring final of having a resistance of say 1.92Ω then at the centre of the ring the load on both legs will be even with an impedance of 0.96Ω. However for the first 10 meters or so if there are sockets available then if the full 32A is drawn then over the permitted 21A will be drawn from one leg. It is up to the kitchen designer to ensure heavy usage appliances are not grouped to one end of the ring final, the person responsible for the design has to ensure where a ring final is used for kitchen appliances the load is reasonably even distributed. Since we have dedicated bays and dedicated sockets in the kitchen this is possible, as to if every electrician actually does consider this is something else, but they have signed that they have by signing the installation certificate.
Where the problem arises is where the house holder decides they don't like the kitchen lay out and want to alter the design. To be frank I can't see where food and dirty washing should be mixed? Why we put a washing machine and a tumble drier in a kitchen I don't really know.
And clearly others have the same idea. Walk up and down my street you will see washing machines and tumble driers in many of the garages very few actually have cars in them, many also converted into extra rooms. Now this is where we start having a problem. Lucky my house has the cables where it is hard to access them in the garage so sockets for washing machine, tumble drier or electric car charging points have to come direct from the consumer unit.
Since a tumble drier is only 3kW and the same with washing machine it would take washing machine, tumble drier, oven, and dish washer all on the end/start of a ring final to cause an overload likely to damage cables which would be rare. Other than a fault I have never had my MCB trip on the ring finals 32A well more like 40A to cause a MCB to trip is quite a heavy load. For the normal house there are only two items which can be run off a 13A supply which will draw over 2kW for any length of time these are the immersion heater and the tumble drier the latter also includes washer/drier of course.
There is little difference between the immersion heater and the tumble drier load wise, and so either we don't need a dedicated supply for the immersion heater or we do need one for the tumble drier.
The oven often has a dedicated supply but this is more because some exceed the 3kW we can draw from a 13A plug than a 3kW or less overloading the ring final. From switch on within 10 minutes the oven with start to cycle on and off, the same with washing machine, and dish washer. Same applies to kettle of course.
Problem with tumble drier we don't really know how long it will draw heavy current for? Mine is set for 1 kW and runs for longer as a result, but no option on my mothers washer/drier to limit the power and really not a clue if it cycles the heater on and off or if it's on all the time? So as the person responsible for design we must allow for the tumble drier drawing max amps for 2 hours even if the actual model fitted does not draw that power for that long.
As to kitchen fitter being responsible for his design! This is always a problem get a house with 4 down stairs rooms and wire up sockets and often the other hard ware is not installed. So we use a supplied plan, then the new owner decides they don't like the layout and ask the builder can I swap x for x likely he says yes without even telling the electrician. I know I have come to second fix houses and needed to phone up to try and work out what has happened. It is rare for the cistern to move it seems the plumbers have more say than electricians and swapping position of an immersion heater supply is rare. But today it is common to go into a house and even if the socket is not marked washer or drier pipe work and grid switch labels do show what each bay was designed for. My parents house had just two fixed items in the kitchen. The sink and the cooker. There were no work tops or cupboards dad had to make them. He had 5 sockets on the ring final, plus a 15A socket for the immersion heater, and lights, plus a spare fuse for later use. Cooker ran on coke. So even in 1954 the immersion had a dedicated supply.
I would consider a kitchen ring final to be dedicated to kitchen appliances so would not be included in the appendix 2 kW suggestion.
If we consider the ring final of having a resistance of say 1.92Ω then at the centre of the ring the load on both legs will be even with an impedance of 0.96Ω. However for the first 10 meters or so if there are sockets available then if the full 32A is drawn then over the permitted 21A will be drawn from one leg. It is up to the kitchen designer to ensure heavy usage appliances are not grouped to one end of the ring final, the person responsible for the design has to ensure where a ring final is used for kitchen appliances the load is reasonably even distributed. Since we have dedicated bays and dedicated sockets in the kitchen this is possible, as to if every electrician actually does consider this is something else, but they have signed that they have by signing the installation certificate.
Where the problem arises is where the house holder decides they don't like the kitchen lay out and want to alter the design. To be frank I can't see where food and dirty washing should be mixed? Why we put a washing machine and a tumble drier in a kitchen I don't really know.
And clearly others have the same idea. Walk up and down my street you will see washing machines and tumble driers in many of the garages very few actually have cars in them, many also converted into extra rooms. Now this is where we start having a problem. Lucky my house has the cables where it is hard to access them in the garage so sockets for washing machine, tumble drier or electric car charging points have to come direct from the consumer unit.
Since a tumble drier is only 3kW and the same with washing machine it would take washing machine, tumble drier, oven, and dish washer all on the end/start of a ring final to cause an overload likely to damage cables which would be rare. Other than a fault I have never had my MCB trip on the ring finals 32A well more like 40A to cause a MCB to trip is quite a heavy load. For the normal house there are only two items which can be run off a 13A supply which will draw over 2kW for any length of time these are the immersion heater and the tumble drier the latter also includes washer/drier of course.
There is little difference between the immersion heater and the tumble drier load wise, and so either we don't need a dedicated supply for the immersion heater or we do need one for the tumble drier.
The oven often has a dedicated supply but this is more because some exceed the 3kW we can draw from a 13A plug than a 3kW or less overloading the ring final. From switch on within 10 minutes the oven with start to cycle on and off, the same with washing machine, and dish washer. Same applies to kettle of course.
Problem with tumble drier we don't really know how long it will draw heavy current for? Mine is set for 1 kW and runs for longer as a result, but no option on my mothers washer/drier to limit the power and really not a clue if it cycles the heater on and off or if it's on all the time? So as the person responsible for design we must allow for the tumble drier drawing max amps for 2 hours even if the actual model fitted does not draw that power for that long.
As to kitchen fitter being responsible for his design! This is always a problem get a house with 4 down stairs rooms and wire up sockets and often the other hard ware is not installed. So we use a supplied plan, then the new owner decides they don't like the layout and ask the builder can I swap x for x likely he says yes without even telling the electrician. I know I have come to second fix houses and needed to phone up to try and work out what has happened. It is rare for the cistern to move it seems the plumbers have more say than electricians and swapping position of an immersion heater supply is rare. But today it is common to go into a house and even if the socket is not marked washer or drier pipe work and grid switch labels do show what each bay was designed for. My parents house had just two fixed items in the kitchen. The sink and the cooker. There were no work tops or cupboards dad had to make them. He had 5 sockets on the ring final, plus a 15A socket for the immersion heater, and lights, plus a spare fuse for later use. Cooker ran on coke. So even in 1954 the immersion had a dedicated supply.
I've long felt that the best circuit for kitchen appliances is a radial.
Because most people have nowhere else to put them.
Because many people find that the rooms in their house are just too small, and/or that there simply isn't enough storage space. Many houses built these days don't even have enough storage space for there to be anywhere to put a vacuum cleaner. And the garage is probably not big enough to put a car in anyway, not if you want to be able to get in and out of the car except via the sunroof once you've driven in.
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Your right specially about size of garage. First house had a car port which was a far better idea for the car. Wind dried the car and enough room for every one to get in before we started. And kick the car out and better than any tumble drier and cheaper to run.
As to radials yes I have talked a lot about the idea with my son. Makes a lot of sense all around the house after the 1/3 rule came in for drilling beams. I remember a housing estate where the builder started using the joists with knock outs for cables and pipes really easy to wire with. So electrical firm designed the installation then (before Part P) put semi skilled labour to wire up. Using one guy who would travel from site to site inspecting and testing.
All was going well until the builder swapped to using standard wooden beams. Two houses were wired before the inspecting guy realised the loop impedance was too high due to extra cable used and a re-design was required. The house was then split side to side rather than up / down for the two rings and all was then OK. But point is how much cable is used going 1/3 of way into room and back again. With the move from single ring to two and 1/3 rule I am not convinced using the ring final system still saves cable?
However a friend moved into a house wired with 16A radials and found welding set would no longer work. Not sure if that's good or bad!
The whole point is of course we need to design an installation. Be it supply to shed or the ring final the idea of just sticking in some wires and hoping for best is not good enough. For the professional also can prove expensive, the do it again and do it properly, costs money. We all cut corners, we know we did a house that size last year and it was no where near the limit, or it only just made it, so we sometimes don't bother working it out first.
But when we make a mistake correcting is not easy. I found an office with a 4mm² radial. Some one had broke into the radial and extended with 2.5mm² around a room, clearly thinking it was a ring not a radial. On finding I swapped the 32A MCB for a 20A MCB but the fan heaters were tripping the 20A MCB. Before I had time to do anything a fan heater went on fire so they were banned removing the problem.
With errors like above I wonder how far back one can go getting remedial work? Would it even matter if done 20 years ago it is a design error and I suppose you could call back the electrical firm to correct. In the case of a housing estate this could be a lot of money.
Not sure when a house is sold. Can the new owners claim off builders or electricians for a design fault. And more to point can they claim of DIY'ers? In 1979 when my house was built installation certificates were rare, so it was near impossible to work out 20 years down the line who had done what work. However today the installation certificate does protect and incriminate. It shows original wiring and readings so easy to show additions.
However I know the problem working out what was permitted in any one year. What year was earths used for lighting, I know around 1964 but not sure exactly which year. And it's the year designed not the year completed which matters. Plus the wiring regulations are not law. So wire a house today with no earth to lights and trying to show in a court of law that the electrician should re-do the work free of charge is hard. The Part P says BS7671 or similar and the 1963 wiring regulations were similar to today's.
So where I worked where every contract stated all wiring to comply with BS7671:2008 unless written consent is given I could take contractor to court. But without that it would be very hard. Only when some one dies is there a court case, very rare for a court case to be brought against an electrician for domestic without a death being involved, except where they claim to be scheme members and are not.
As to radials yes I have talked a lot about the idea with my son. Makes a lot of sense all around the house after the 1/3 rule came in for drilling beams. I remember a housing estate where the builder started using the joists with knock outs for cables and pipes really easy to wire with. So electrical firm designed the installation then (before Part P) put semi skilled labour to wire up. Using one guy who would travel from site to site inspecting and testing.
All was going well until the builder swapped to using standard wooden beams. Two houses were wired before the inspecting guy realised the loop impedance was too high due to extra cable used and a re-design was required. The house was then split side to side rather than up / down for the two rings and all was then OK. But point is how much cable is used going 1/3 of way into room and back again. With the move from single ring to two and 1/3 rule I am not convinced using the ring final system still saves cable?
However a friend moved into a house wired with 16A radials and found welding set would no longer work. Not sure if that's good or bad!
The whole point is of course we need to design an installation. Be it supply to shed or the ring final the idea of just sticking in some wires and hoping for best is not good enough. For the professional also can prove expensive, the do it again and do it properly, costs money. We all cut corners, we know we did a house that size last year and it was no where near the limit, or it only just made it, so we sometimes don't bother working it out first.
But when we make a mistake correcting is not easy. I found an office with a 4mm² radial. Some one had broke into the radial and extended with 2.5mm² around a room, clearly thinking it was a ring not a radial. On finding I swapped the 32A MCB for a 20A MCB but the fan heaters were tripping the 20A MCB. Before I had time to do anything a fan heater went on fire so they were banned removing the problem.
With errors like above I wonder how far back one can go getting remedial work? Would it even matter if done 20 years ago it is a design error and I suppose you could call back the electrical firm to correct. In the case of a housing estate this could be a lot of money.
Not sure when a house is sold. Can the new owners claim off builders or electricians for a design fault. And more to point can they claim of DIY'ers? In 1979 when my house was built installation certificates were rare, so it was near impossible to work out 20 years down the line who had done what work. However today the installation certificate does protect and incriminate. It shows original wiring and readings so easy to show additions.
However I know the problem working out what was permitted in any one year. What year was earths used for lighting, I know around 1964 but not sure exactly which year. And it's the year designed not the year completed which matters. Plus the wiring regulations are not law. So wire a house today with no earth to lights and trying to show in a court of law that the electrician should re-do the work free of charge is hard. The Part P says BS7671 or similar and the 1963 wiring regulations were similar to today's.
So where I worked where every contract stated all wiring to comply with BS7671:2008 unless written consent is given I could take contractor to court. But without that it would be very hard. Only when some one dies is there a court case, very rare for a court case to be brought against an electrician for domestic without a death being involved, except where they claim to be scheme members and are not.
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I've never been keen on ring final circuits at all, for some of the reasons already outlined (possibility of excess load near to one "end" of the ring etc.). And I much prefer the approach taken here to major appliances, where it's pretty much the norm for each such appliance to have its own dedicated branch circuit. That includes the washer, even though the majority of American machines do not have integral heating elements. I also prefer the idea of a separate utlity room or area for laundry, which has been the norm here for decades.
People here prefer it too.
Most can't afford it.
Most can't afford it.
Indeed. In terms of ideal location, if a separate utility area isn't available I often felt that nearer to the bathroom would make more sense than the kitchen, as preferred in some European countries. Of course, the typical British bathroom probably has even less room than the typical British kitchen for that idea to be popular!
In the common situation of a cable with a (undoubtedly 'conservative') CCC of 27A protected by a 32A OPD, if you do the calculations you will find that you would have to have the entire 32A load very close to one end of the ring to even 'technically' overload any of the cable.
There clearly are pros and cons of ring finals (hence passionate views in both directions), probably the greatest of the 'pros' being the CPC redundancy.
Kind Regards, John
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