On 30/05/2015 14:19, dennis@home wrote:
On 30/05/2015 01:03, John Rumm wrote:
On 29/05/2015 19:02, dennis@home wrote:
On 29/05/2015 11:20, John Rumm wrote:
All that is required is a bit of common sense from the designer of the
circuit, and a user can do as they please.
So three 3kW heaters on the end of a ring then?
Which part about the designer using common sense did you not get?
If you have a kitchen layout like mine, all the sockets are in the
middle of the ring since there is a 20m of cable run just to get there.
If you have a CU in the kitchen then you use a bit of common sense like
if you have a pair of adjacent utility spaces close to one end of the
ring, you make sure you wire the sockets on alternate ends and not
adjacent to each other.
So you want to make it worse as the user now has no idea where the
"close to one end" sockets are?
Den, I know this is a personal crusade of yours to convince the world
there is a problem where it is blatantly obvious that one does not
exist, but at least try and put the effort in - rather than taking the
lazy route of simply being obtuse...
I will say it again for you:
The user has no need to know what socket it where in the cable run. They
plug stuff in, it works.
Now a designer ought to think about it a bit more deeply. They need to
think about what the typical loads are going to be, what the circuit
layout will be, and what type of circuits to provision. For general
purpose socket circuits this is often a ring, but it does not have to be.
Lets say you (the designer) have decided that the kitchen is the place
where most of the high power devices are likely to be installed. The
kitchen layout has three 600mm wide under counter spaces right up
against the end wall - next to the cupboard with the CU in it. Its a
reasonable bet that a user might want to equip the space with DW, WM,
and TD - most of which will be in the 2 to 2.5kW range. So you could
potentially have 6 to 7.5kW of short term load, and say 4kW of medium
term load - close to the origin of the circuit.
So you look at the layout and decide that a ring will suite the space
well. You decide that 7.2kW total long term capacity should be adequate.
Hence you select one ring final circuit. The only thing against this
choice is that you will could end up with much of the load concentrated
at one end if you wired it without thinking it through first.
So being a sensible designer, you think "Ah, both ends of the ring will
need to pass this space", so I will equip three unswitched single
sockets under the worktop, with separate 20A plate switches above the
worktop. The first I will one I will feed at one end of the ring, and
the last pair from the other end of the ring. Thus spacing the loads
out. If you were really worried about an imbalanced load, then you might
even go so far as to place one of them on a spur taken from the origin
of the circuit.
Alternatively you might look at the kitchen and decide this is a galley
style layout - all the stuff on one wall. A more suitable topology would
be a 32A radial backbone running down the length in 4mm^2, with unfused
spurs in 2.5mm^2 cable dropping to each socket.
Why not face it' you just can't cope with idiot users.
And yet all the evidence and practical experience shows that the system
copes with users (idiot and otherwise) remarkably well.
How about adding in the combi microwave at 2kW for a hour while you
cook
some chicken?
So what's that going to average out at? The equivalent of 500W
continuous load?
That depends on which one and what you are cooking, they tend not to be
as well insulated as proper ovens so they use more electricity to do the
same job.
Thus reducing the duty cycle on the fan heaters...
--
Cheers,
John.
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