Jim Green wrote:
My first post so please be kind!
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:
Fridge
Dishwasher
Kettle
Microwave
Toaster
Cooker Hood
The book says unlimited sockets.
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?
Jim
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...
HTH - Stefek
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