UK Kitchen Wiring-New Build ring vs radial

JolyBob · Jun 11, 2023

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 ;-)

pc1966 · Jun 12, 2023

DPG said:
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 · Jun 12, 2023

pc1966 said:
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 · Jun 12, 2023

pc1966 said:
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 · Jun 13, 2023

davesparks said:
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.