UK Kitchen Wiring-New Build ring vs radial

[JolyBob]

HI All,
I am building a new house (self build) and have my part P so am running the cabling. My reading of the regs says that any appliance of over 2KW should not be supplied by a ring main and should have a 4mm radial. (BS 1363)

My questions are really around this- - It seems all of my appliances exceed 2KW- So I have allocated each circuit to not exceed 30A. This gives three radial’s.

Radial 1- 2 Cookers (3KW and 3.5KW)
Radial 2 – 2 cookers (3KW and 3.5KW)
And Radial 3 - Fridge freezer 10A, 2 x dishawashers @10A each,
The Quooker (that says its only 10W?!) and drinks fridge I am suggesting to be on switched fused spurs from the ring main.

I also have washing machines and dryers going into the utility- do these also need their own dedicated radial? as once again they exceed 2KW Or have i misread the regs?
See attached all feedback welcome ;-)

 

[Dustydazzler]

In a brand new build I would just run in lots of 4mm radials to all the various positions. You can have a bank of 20amp circuits on Rcbos each identified what they serve at the consumer unit.
almost exactly how they do their wiring in pretty much every country in the world

 

[pc1966]

The 2kW limit is really intended for the likes of immersion heaters that can draw that sort of power for hours at a time. Obviously for socket-outlet circuits in the UK the limit is 3kW = 13A per appliance.

Anything that takes over 3kW should be on a dedicated circuit, that could be using 4mm to 16mm cable depending on the circumstances. Quickest route is to check the on-site guide for combinations that are acceptable for your appliance load/OCPD, cable length and installation method.

As far has multiple radials versus RFC for socket/FCU-fed appliances it gets a bit religious. The comment about "almost exactly how they do their wiring in pretty much every country in the world" forgets that most of the rest of the world does not have fused plugs and so they are forced in to 20A or less OCPD and thus the diversity benefit of 32A to share over multiple variable loads, and cost savings of 2.5mm RFC in doing so, are simply not an option there.

If you want to see the debate then go here rather than starting anew:

Ring Final Circuit (RFC) versus Radial. Yes, again. - in - Electrical Engineering Chat

, Ring Final Circuit (RFC) versus Radial. Yes, again., Electrical Engineering Chat, ElectriciansForums.net Est.2006 | Free Electrical Advice Forum and page_number.

www.electriciansforums.net

 

[pc1966]

In terms of kitchen design though a far more important detail is to have accessible means of isolation for all white goods (as well obviously for hard-wired stuff like cookers). That is now part of the Scottish building regulations but I don't know if England & Wales has anything similar.

So put 20A isolator switches above the worktop and then a 13A unswitched socket behind each fridge/dishwasher/washing machine or similar.

 

[Simon47]

Do those regs say where the isolators have to be ?
If the CU is accessible then you have a means of isolation.

 

[DPG]

Do those regs say where the isolators have to be ?
If the CU is accessible then you have a means of isolation.

Local isolation is preferred to avoid knocking a whole circuit off.

 

[pc1966]

Do those regs say where the isolators have to be ?
If the CU is accessible then you have a means of isolation.

The intention is an "ordinary person" is able to switch anything off if there is a problem, or just for extra safety when doing any maintenance and without having to move a 50kg washing machine loaded with water, etc. Using the CU is fine for a sparky or competent DIY'er but not want most folks would think of under panic conditions.

I expect they would have to be accessible to a wheelchair user under building regs for any part of UK, so that limits height range and not being in cupboards, too close to corners, etc, that are unreachable from a chair.

Also you should think about what a visitor might need to do, or a future owner, not what you as the installer knows about the setup. My own preference would simply be above the appliance as then it is fairly obvious what it might do.

Some folks like the look of grid switch arrangements but others say they lack the reliability of typical stand alone isolator switches. If grid switch (also some stand-alone 20A isolator switches) you can buy switches engraved with functions like "fridge" and so to to make it clearer.

 

[pc1966]

Scottish regs are here:

Building standards technical handbook 2022: domestic

Scottish Government building standards technical handbook for domestic buildings, 2022.

www.gov.scot

Section mentioning this aspect is final section:

Electrical fixtures - outlets and controls of electrical fixtures and systems should be positioned at least 350mm from any internal corner, projecting wall or similar obstruction and, unless the need for a higher location can be demonstrated, not more than 1.2m above floor level. This would include fixtures such as sockets, switches, fire alarm call points and timer controls or programmers. Within this height range:

• light switches should be positioned at a height of between 900mm and 1.1m above floor level
• standard switched or unswitched socket outlets and outlets for other services such as telephone or television should be positioned at least 400mm above floor level. Above an obstruction, such as a worktop, fixtures should be at least 150mm above the projecting surface

Where sockets are concealed, such as to the rear of white goods in a kitchen, separate switching should be provided in an accessible position, to allow appliances to be isolated.

 

[pc1966]

So they don't say exactly where, but again I would apply the principle of least astonishment to it.

 

[JolyBob]

Isolations switches goes without saying- It really is about what i can have as spurs of my ring main - and what I need radials for. This is a BC question. I don't want to run in all my cables just for some BC inspector to say "well you cant do that you muppet"

 

[pc1966]

Isolations switches goes without saying- It really is about what i can have as spurs of my ring main - and what I need radials for. This is a BC question. I don't want to run in all my cables just for some BC inspector to say "well you cant do that you muppet"

Having an isolator switch then socket off an RFC is no different from the usual spur so you can have those at any point on the RFC. I.e. if you were putting in 4 white good points, each with an isolator switch, you would run the RFC to each switch's input (as if a socket) then have a single 13A socket off the switch output.

If you have an RFC just for the kitchen, for example, then all appliances are roughly half-way so balance is always very good. Some prefer a radial in 4mm (method permitting) to also have 32A for cases when the total load that could well exceed 20A. Swings and roundabouts really, 2.5mm is easier to wrangle at back boxes and allows a few more "installation methods", but you then have the final run back to the CU to do. Or if thinking ahead, run both legs from CU to kitchen and then close round there, etc.

The don't-do of RFC is to spur off more than a double socket. Better still, don't spur off anything without a very good reason (like isolator switch, etc) as you lose some of the advantages of better fault coverage when testing.

 

[mattg4321]

Either way, I’d be running a ring for general use sockets and small loads like extractor/gas hob ignition etc and 16A 2.5mm2 radials to appliances (unless over 16A of course)

 

[davesparks]

My reading of the regs says that any appliance of over 2KW should not be supplied by a ring main and should have a 4mm radial.

No, there is a recommendation for certain types of appliance over 2kW to have their own circuits, there is no requirement for those circuits to be 4mm radials.

.
Radial 1- 2 Cookers (3KW and 3.5KW)
Radial 2 – 2 cookers (3KW and 3.5KW)
And Radial 3 - Fridge freezer 10A, 2 x dishawashers @10A each,

Splitting 4 cookers across 2 circuits seems reasonably sensible.

I would put the fridge freezer on its own circuit to reduce the risk of it going off when a fault occurs in another appliance.

 

[pc1966]

I would put the fridge freezer on its own circuit to reduce the risk of it going off when a fault occurs in another appliance.

That aspect is kind of swings and roundabouts now that RCD is pretty mandated for all domestic circuits.

• Advantage of separate radial - fridge stays on if something else trips the RFC, etc.
• Disadvantage of separate radial - if fridge circuit is tripped (e.g. from power surge, etc) you don't notice until you go to said fridge and find it de-thawing.

 

[DPG]

Just to confirm, ylu

That aspect is kind of swings and roundabouts now that RCD is pretty mandated for all domestic circuits.

• Advantage of separate radial - fridge stays on if something else trips the RFC, etc.
• Disadvantage of separate radial - if fridge circuit is tripped (e.g. from power surge, etc) you don't notice until you go to said fridge and find it de-thawing.

You'd tend to notice that the light in the fridge part didn't come on though.