Need to start new kitchen circuit wiring before 1st Jan. You all know why!
According to my (slightly old) DIY book I can use 2.5mm T&E with a 20amp MCB for a maximum floor area of 20 square meters. My CU is in the kitchen pantry so the total floor area the cable will cover is definitely less that 20 square meters. On this circuit I plan to have:
On Wed, 15 Dec 2004 10:55:03 +0000, Jim Green strung together this:
Because you get an extra 10A for an extra length of 2.5mm. 20A might sound ample but it isn't that much when you start putting the dishwasher\kettle\toaster on. It won't take much extra effort to make it a ring so I can't see any reason not to, the only place I use a radial circuit is in a low load area, such as bedroom or dining room.
The current OSG gives a maximum recommended area of 50 sq meters.
No reason at all *except* that the loading is probably getting pretty close to the 20 amps maximum on a 2.5sq mm radial. The kettle alone takes 12 amps or thereabouts.
The recommendations in the OSG etc. are just that, recommendations. For kitchens in particular the maximum load on the circuit (or circuits) may mean that you need more circuits than would at first seem reasonable.
That said I much prefer 2.5sq mm radial circuits to ring mains in many cases. They have several advantages:- No need to limit the number of spurs, the whole thing is (quite legitimately) a multi-branched spur.
No need to check whether sockets are on spurs or 'on the ring' when adding extra sockets.
Easier routing of cables as there's no necessity to make a ring.
Possibly more separation of different areas into separate circuits.
I have a separate 20 amp MCB radials for the following:-
Study, lots of computers etc.
Daughter's bedroom, was an extension so added a circuit to supply it.
Garage.
Other outdoor circuits.
If I was starting from scratch I think I'd go for all radial circuits except possibly in the kitchen where the extra capacity of a ring dedicated to the kitchen may be useful/necessary. (Though you could, I suppose, go for a radial wired with 4sq mm)
"Jim Green" wrote | >>Now my question is purely theoretical as I am going to do a ring | >>circuit instead. But given the above why should I make it a ring | >>circuit? | > Because you get an extra 10A for an extra length of 2.5mm. 20A might | > sound ample but it isn't that much when you start putting the | > dishwasher\kettle\toaster on. | So unlimited sockets doesn't actually mean unlimited sockets. It means | unlimited sockets so long as the majority are turned off!
It means unlimited sockets assuming the majority are only used for low power appliances - which is true in most situations. The modern kitchen is an exception. When the 13A socket system was designed in the 1940s, deep fryers, dishwashers, kW+ combi microwaves, etc, weren't really taken into account :-)
You might want to run a separate, non-RCD, circuit for the fridge while you're at it. And put in provision for an electric cooker at the same time. Even if you don't use it, a future owner of the house might appreciate it.
As I mentioned yesterday, the UK approach to wiring regs is based on general principles and guidance on meeting them, rather than a rigid code. The 20sqm-floor-area is an example - it's *guidance* for *typical* loading, dating from some years ago, not a substitute for thought.
So, let's do "thought" instead. The loads you'll be putting on this circuit aren't trivial, but they won't be drawing their full currents for long periods. Specifically: dishwash - 1.5kW (say) while heating water, but doesn't do it for more than 10 minutes at a time; kettle -
2kw or 2.5kw while on, doesn't stay on for more than 5 minutes at a time; microwave - a tad under 1kW while it's on; toaster - not vast, maybe 0.5kW while it's on. Cooker hood - minimal; fridge - 0.3kW or so, coming on and off under thermostatic control.
So worst-case (all appliances drawing full load at once) there's 5 or
6kW; each 1kW is 4A (close enough) so that's 24A at peak. Since the conditions under which that peak load's drawn won't last for more than a few minutes, you could "get away" with a 20A-fused 2.5mmsq radial. And hope you or the next householder doesn't add a washing-machine, rice-cooker, breadmaker, or similar.
I wouldn't, though. I'd allow for "growth"/additional appliances later, and would provide the kitchen with a dedicated 32A appliance circuit, either as a ring with 2.5mmsq or a radial with 4mmsq. Unless there was a long distance from kitchen to CU, the ring would be my default, as
2.5mmsq is very widely available (and full reels are always on "special offer" at any trade counter ;-), and easier to work with (esp. if you find it sensible to run a spur up to the FCU for the cooker hood - stuffing 3 x 4mmsq into socket terminals and neatly into the back box takes some doing). And for a 4mmsq radial with 32A protection, you should really do the calcs to show the length is consistent with tripping times...
Lastly, there's the RCD protection issue. The Regs say sockets which it's "reasonably foreseeable" will supply outdoor appliances should have RCD protection, and most interpretations say you should presume that all ground-floor sockets are in such a category. (It's only a presumption in an interpretation, mind: if, for example, the outside of the house has several dedicated outdoor sockets at convenient locations, it's reasonable to rebutt said presumption ;-) Perfectionists sometimes argue for non-RCDed supplies to fridge, freezer, and maybe fixed appliances, while providing RCD protection on sockets for the portable appliances - kettle, mixer, and the like. For me, there's never quite so much irreplaceable food in the fridge/freezer coupled with long periods away from the house to want to separate the refrigeration supplies from the others, but You May Know Different...
There is a concept called "diversity" that comes into play here. If you think about it, a 30 amp circuit could be over loaded from a little as three sockets feeding large 13A loads, however there may in fact be far more than three socket outlets installed. Hence the designer of a circuit will provide enough capacity to cope with typical and likely loads, not the theoretical maximum load.
The wiring regs say a final ring circuit can cover an area of up to 100 sq m and have as many socket outlets as you want. However you need to design what you actually install based on anticipated loading. Hence a kitchen, which often has a high concentration of power hungry devices, if often given a circuit all to itself.
The square metre suggestions (which you have the wrong figure for) are only appropriate for normal living spaces, not for kitchens. They are basically about how much power you would need to heat the house in an emergency with thermostatically controlled fan heaters. A kitchen, with many high powered heating appliances requires far more capability.
You can't have all the appliances you suggest on a 20A circuit. You just can't. It will probably trip frequently.
Also, some of the appliances should not be RCD protected, some could swing both ways, but others should be RCD protected (not a requirement of the regulations, just common sense).
For a kitchen, I would normally suggest 2 or 3 32A ring or radial circuits. One ring should be RCD protected and provide all the socket outlets for portable equipment such as kettles and non-built in microwaves. The other ring should be not RCD protected and provide all the fixed major appliances, such as laundry and refridgeration appliances. I would normally split this into 2 and have an entirely separate 16A circuit just for refridgeration. This is just to minimise the possibility of a trip on the freezer circuit ruining all your food.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.