On Mar 10, 10:15*pm, "Lieutenant Scott" wrote:
On Sat, 10 Mar 2012 21:40:14 -0000, John Rumm wrote:
On 10/03/2012 20:30, Lieutenant Scott wrote:
On Sat, 10 Mar 2012 20:10:38 -0000, NT wrote:
On Mar 10, 7:54 am, "ARWadsworth"
wrote:
Lieutenant Scott wrote:
I see. Why are lighting circuits never rings, and why does the
lighting wire sold in DIY stores always seem to be rated at 16 amps
ish, while I've never seen a lighting circuit have a fuse/breaker of
anything other than 5/6A.
The point of the ring is to allow 20A cable to form a circuit that
safely
uses a 32A MCB.
There would be no point in doing that is you were using 16A cable
with a 6A
MCB
10A is probably the largest size MCB you will see in a house for the
lights.
You might see 16A used in factories etc. BTW it's not 16A lighting
cable,
look at
http://wiki.diyfaq.org.uk/index.php?...es#Cable_Sizes
If one went with 6A lighting rings, using lets say 3.5A cable, it
could be:
only when not buried in insulation: 0.33mm2
buried: 0.44 mm2
For the cfl/led only user, we could reduce a 10 room lighting ring
down to... say 50w per room allowance = 500w = 2A and use 1.3A cable,
0.16mm2 would work even if buried in insulation.
I'm using 26 watts (four 75W equivalent spots) in this room and it's lit
very brightly.
Many rooms will use less than 50w of CFLs, leaving a higher budget for
the larger rooms. One could budget 20w max for small rooms like loo &
bathroom.
And the use of RCDs would enable the earth conductor to shrink to a
similar size. Shock voltage would go up, but the RCD would limit it to
such brevity as to be safe.
Voltage goes up? How?
If you are getting a shock from something due to a fault (i.e. touching
something made live by a fault, or "indirect contact" as it used to be
known). Then you can assume that the earthing will ensure the fault is
cleared quickly, and that limits the shock duration.
However you also get fortuitous equipotential bonding effect brought
about by the earth connection that will tend to lower the touch voltage
(if you imagine two lengths of wire of equal CSA - one connected to
earth (0V) and one to mains, you would expect the the arrangement to act
like a potentiometer wire, and the voltage with respect to earth would
be half mains at the fault). If you start making the resistance of the
earth larger (i.e. by making it thinner), then the touch voltage at the
fault will rise.
Not if the live is also thinner.
True. With very thin wire its cheap to have equally thick earth wire,
which would make shock voltage lower than today's T&E circuits. As
long as the shock didn't come from a 30A circuit, in which case the
lighting earth would probably vapourise. But the RCDs should protect
it and clear it at some point.
One could go even further: with an RCD there's very little theoretical
need for double insulation or earthing, one could simply use very thin
speaker wire.
It's the fire hazard that would concern me more. Speaker wire could get
snagged easily.
a tad over 2A is unlikely to do it much harm...
A minor short could easily occur if it's flimsy wire, which can cause a fire.
Either don't make the insulation flimsy, or do and have a little
consideration for where the wire goes. Bell wire isnt damaged by
normal use and abuse - but then its far from 0.16mm2.
Conductors can easily be reinforced by simply including string in the
cable. Another approach I'm a lot less sure about is to use copper
clad steel to increase conductor strength.
Anyway, if you're not earthing, then brass lighting fixtures wouldn't be
protected against loose live wires,
The RCD does that. Or one can mandate only plastic and double
insulated metal fittings on such circuits.
plus that annoying guy that checks
your house when you sell it would put a red X on a few parts of his report.
Not if such a scheme were accepted. Here I'd be quite happy in
principle for lighting to go on a 3 core 2A bell wire ring, for CFL
users its perfectly effective and safe, as long as its installed
correctly. For 2nd world applications one could dispense with the
earth conductor, relying on RCD and fitting insulation. For 3rd world
one could reduce conductor size to 0.16mm2 and reduce insulation to
speaker wire proportions.
That is what the RCD was designed to mitigate.
RCD won't pick up you touching live and neutral. *With the earth it's more likely you touch earth instead/aswell, which will trip it.
There's no safety scheme in use that I know of, at least in domestic
properties, that offers any L-N shock protection beyond insulation. L-
N shocks are excepional.
Anyway, if you are blue
sky thinking, you can do away with the surveyor! (not that they ever do
much other than say of you want the electrics checked, get a specialist)
Just how do you do away with a surveyor commissioned by the buyer of your house?
I dont see any point in installing such things unlawfully. Its only
useful when widespread and accepted. Call it an eco-circuit for
acceptance. FWIW surveyors dont check electrical installs. If you
wired your house up with iron wire in hosepipe they'd say the same
thing as always, get the electrics checked.
Current practice is to supply just an 8A feed per flat in at least
some of the eastern bloc,
For the entire flat or just the lighting?
Entire flat I would expect. 8A for lighting would hardly be exceptional....
Yes, the whole flat. I've seen it in aluminium, it looked like fatter
bellwire.
I'd find it very difficult to keep to 8A. *So that's no cooking then?
A medium performance ring can run on 1kW. A microwave sized fan oven
does fine on 1kW. 1kW consumption microwaves with about 400w cooking
power exist in Britain, they work adequately.
I've cooked on 500w rings too, 3rd world type equipment with bare live
elements. Its way too low to be practical, a pan of water takes 20
minutes.
No electric kettles?
8A is 2kW, no problem with kettles.
I saw an eastern bloc kettle with a speaker wire type lead (a few
minutes doesn't need much copper) and no element. Instead there were
just 2 bits of metal at the bottom connected to L&N, it was an
electrode kettle. I'd prefer a real 1kW kettle though.
A kettle that was 5 or 600w was ok for a cup or 2, but too slow when
full.
*Even a hoover is using most of that allowance.
typical hoover from the 70s uses about 500w. You can get modern
effective ones that use under 200w (Oreck). Or just use a powerful 1kW
machine.
*I wonder how many nails get put in the master fuse holders.....
(having said that, DNOs often design their distribution systems on the
assumption that the diverse load of each house is something around 8 to 10A)
In this country?
Its actually easy to live on 2kW max, or less. Its just a matter of
choosing your appliances with a clue or two, and adopting a policy to
avoid overload. It only takes a little thought to massively trim down
our luxury consumption levels. Even washing machines work well enough
with a 1kW element - they don't spin and heat at the same time.
NT