UK Kitchen Wiring-New Build ring vs radial

[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.

 

[pc1966]

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

Assuming you use the fridge often enough. Probably OK in my case as cups of tea needing milk are common, but for a freezer-only that you check once or twice a week more of a concern.

I presume you get loss of power alarms for this sort of thing, but never looked/found that yet.

 

[DPG]

Assuming you use the fridge often enough. Probably OK in my case as cups of tea needing milk are common, but for a freezer-only that you check once or twice a week more of a concern.

I presume you get loss of power alarms for this sort of thing, but never looked/found that yet.

Yeah freezer only is a problem

 

[davesparks]

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.

Do power surges actually trip RCDs? And wouldn't the wonderful mandatory SPD sort that out now?


Domestic fridges should hold their temperature for at least 12 hours so it should be discovered in normal use before all is lost.


Just to be pedantic I think thawing would be the problem, de-thawing would imply it is getting colder

 

[pc1966]

Do power surges actually trip RCDs? And wouldn't the wonderful mandatory SPD sort that out now?

Some models seem to be sensitive to dV/dt surges more than others. SPD ought to keep some of that down if due to a lightning spike (at least limiting 'V' so dV is a bit less).

I guess the real world risk is small, but that is the sort of thing we fixate on here as designing for fault handling is an essential aspect of safety. But flip side of that is risk of socket circuit tripping and not being noticed (or happening when on holiday, etc) is also pretty low.

Just to be pedantic I think thawing would be the problem, de-thawing would imply it is getting colder

True! I had never really thought about that expression before