Denny,

(I know this is a late reply - I was born a fortnight late, and I've never =
managed to catch up... )

On Wed, 18 Oct 2006 23:56:17 -0400, Denny Esterline wrote:

> I read the history of British electrical systems once and as I recall, th=
e loop system was implemented to save metal. Since any plug is actually fed =

from both sides of the loop the wire only needs to be rated for ~1/2 the to=
tal current. =


Yes, although there is quite a bit of headroom on the "half" - the most com=
mon ring final will have a 32A Miniature Circuit Breaker (MCB) and will be =

wired in 2.5mm=B2 Cross-Sectional Area (CSA) "Twin & Earth" cable, which lo=
oks like this: =

http://www.tlc-direct.co.uk/Images/Products/size_3/CA2.5GH.JPG  As you can =
see, the Earth core is uninsulated, but it will be covered with a =

green/yellow sleeve within the backboxes of any socket, switch, etc.  It ha=
s a free air rating of 27A (if my memory serves), although this is reduced =

in most real-world installations to 23A, as you can see there is plenty of =
headroom.

> Ours is a single ended daisy chain, so the wire must be rated for the ful=
l current. But we only have a fuse/breaker at the service panel, so the sum =

current of the entire string can't exceed the rated current. In practice ha=
ndheld appliances seem to rated less than 1500W (hair dryers, electric fry =

pans, tea kettles etc) =


We call this a "Radial" circuit, and they are used for lighting (which is a=
lways separate from power circuits), and for single-appliance circuits such=
 as =

electric cookers.  They can be used for strings of sockets, but because you=
 have to use thicker cable (typically 4mm=B2) it's unusual - a 2.5mm=B2 rin=
g is =

much easier to work with.

> > If you're doing something industrial that needs more than 3kW you can e=
ither hard-wire, or use industrial plugs which handle 16 or 32A, but you'd =

> > never normally see those in a house or garage, even a garage-workshop.
> > =

> =

> Most commonly circuits are 14ga wire and rated for 15 amps. Some specific=
 circuits are rated for 20 amps and use 12ga wire (I believe it's 2 in the =

kitchen by local code) and usually in the utility area (garage, basement, o=
utdoor...) =


Interesting!  There are calculations to determine the wire CSA to use, ther=
e are no hard and fast rules as above.  Here's a web site that calculates i=
t =

for you:  http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

We have no regulations here about how many circuits are provided, or where =
- my own house has two power rings, upstairs and down (32A each), =

and had a single lighing circuit for the whole house, but I split this into=
 two when I installed a new Consumer Unit (I think you call this a distribu=
tion =

board?) back in 2004 when it was still allowed to do this without Building =
Control approval.  Then there's a radial for the immersion heater and =

another one for the fridge/freezer (16A each, the latter so that a trip cau=
sed by a fault elsewhere while I'm away won't mean all my food goes bad!).  =

Then there's the shed...

> But just to make things complicated they fit the same plug. (there are di=
fferences between 15 and 20 amp rated sockets, but the consumer can't =

tell the difference by looking) It's still safe though, because a 15 amp so=
cket is protected by a 15 amp breaker. But it can certainly be annoying.

I was a bit amazed at my girlfriend's house in New York to discover that a =
single 15A breaker powers the ground floor lights, all of the kitchen excep=
t =

the fridge/freezer, the dining room and the living room sockets.  I discove=
red this when I tried to use the microwave and the toaster at the same time=
, =

and it all went dark and quiet!  :-)  At home if I use my microwave (1kW) a=
nd electic kettle (2.2kW) together it doesn't even come half way to the =

downstairs ring's current rating - it would never occur to me to be careful=
 how much I use at once!

Having read some of your NEC, it strikes me that it's focus is almost all o=
n prevention of overheating and fire - over here prevention of electric sho=
ck =

has at least the same emphasis, if not more.  And it seems to rely on activ=
e safety devices like GFCIs (which we call RCDs), rather than the design =

and installation being naturally safe - for example sockets aren't allowed =
in a bathroom (to the annoyance of my girlfriend because she can't use a =

hairdryer in there :-) except special 1-Amp-fused 2-pin sockets supplied fr=
om an integral isolating transformer, for electric shavers and toothbrush =

chargers, such as this one: http://www.tlc-direct.co.uk/Images/Products/siz=
e_3/MKK701.JPG.  Interestingly it's dual-voltage, so visiting Americans can =

charge their toothbrushes!  :-)  This is the only place you'll find 115V in=
 a UK house.

>...
> Another interesting quirk is the voltage. It's common to talk about 110/2=
20, but some people say 120/240. The plug next to me actually measures =

117V. Some other places I've lived were closer to 110V and I worked in one =
place that measured 124V. And even though the USA is "standardized" on =

60 Hz, I believe there are a couple small islands up near Maine that use 50=
Hz and last I knew there was a generator plant at Niagara Falls that =

produces 25Hz for a few industrial customers.

124V on a nominal 110V sounds a bit out of spec!  Is there a published allo=
wable range?

Ours is all 50Hz, and as has been discussed it's *nominally* 230V, but mine=
 is currently at 244V, which isn't unusual.

Cheers,

Howard



-- =

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