Jim Michaels wrote:
Hi,

I will assume that your post is not bait and is serious

You make some good points, but there are a few I'll pick up on:


On Wed, 1 Jun 2005 10:31:18 +0100, "Christian McArdle"
wrote:

The US electrical system is simply unsafe compared to the rest of the world.

true, at least compared to UK. Maybe not the world, US seems the model
of good practice compared to African practices, and that of many other
countries.


Current, of course). Edison's first great central station, supplying
power for three thousand lamps, was erected at Holborn Viaduct,
London, in 1882. Does anyone know the voltage that was used? In any
case the U.S. Voltage is due to historical factors. I am sure the
British voltage was not selected much more recently.

but this doesnt change the fact that 110 is inherently more dangerous
than 240. With 240v we treat it with respect, with 110v people relax
since it wont electrocute them, and hurts waaay less if they get bit.
They worry less about cord grips etc. The result is fires, which are
the prime killer, not electrocution.


The basic issue is that
very few people die of electrocution, whilst loads of people die from
electrical fires. The electrical fires largely stem from high currents. If
you halve the voltage, you double the current.
NOT TRUE.
You are making multiple invalid assumptions.
1. That U.S. wiring has the same number of circuits for the same load.

still cant figure out what you mean there. For a given load you do have
higher i with lower v, and each load is on 1 circuit as far as i can
see.

2. That U.S. circuits are not designed for their load.

I dont think that was the assumption: the problem is simply theyre
designed to have a higher incidence of faults. The practice of push-in
connection on mains sockets is something considered unthinkable here,
for good reason. Use of single insulated mains flex has been illegal
for decades, etc etc.


3. That electrical fires occur in properly designed circuits simply
due to higher currents.

we know its due to many factors.


4. You claim lower voltage equals higher current, then you say...
The high voltage has other safety benefits, too. For example, during an
earth fault, the higher voltage leads to much higher current flow. An
overcurrent safety device is, thus, much more effective, leading to much
more rapid disconnect of the circuit.

It seems you contradict yourself.

no contradiction there that i see, just an example of how higher v
gives a safety benefit.


If the breaker requires 5x current to trip
immediately, this requires an earth impedence of 0.73 ohm right back to the
substation.


Note: Our circuit breakers magnetic trip are similar to your type D

should give less nuisance trips, ours sometimes trip on bulb failures.


The
required earth impedence is now 3.8 ohms. This is extremely easy to achieve,
unlike the 0.73 ohm, which might even be impossible.

Again, in the U.S. a 3kW circuit would be 240V 15amp and the same
benefits would apply.

In US IIUC it would be called 240v, but in fact be 120-0-120, so the
voltage from earth is 120 ac, not 240. In which case the fault
clearance benefit of genuinely 240v would sometimes apply and sometimes
not. Some faults that smoulder at 120 can arc over and trip at 240.


Another effect of the low voltage is that "respect" for electricity is
lower. The lower voltage leads to lower quality insulation on fittings,
cheaper parts and a blase attitude of users to electrocution. The result of
this is that the US actually has a higher electrocution death rate per
capita than the UK, despite the lower voltage! When you compare the
incidence of electrical fires, the differences become much more scary.

Please quote sources for statistics.


2. Use of wirenuts.
Why Not?

they were banned here long ago because they cause connection failures
and fires. They dont provide anywhere near the clamping pressures of
our screw connections.


3. Combination of neutral to earth (i.e. effectively TN-C earthing) leading
to electrocution in the event of polarisation swap, or some open circuit
conditions.

snip

In the past it was permitted for the neutral to be used to ground the
frames of ranges and dryers.
This came about as Interim Amendment No. 53 put into effect on July
10, 1942. This was to allow the neutral to ground the frames by means
of a bonding jumper from the frame to the neutral. The reason for the
amendment was to save raw materials like rubber and copper for the
effort of WWII.

that much is fair enough, but...

This special amendment however was not removed from the NEC until the
1996 code cycle.

remarkable. At least not something normally permitted here. But we do
have a permited 2 conductor wiring system, I forget the details, ISTR
maybe it uses MICC? I'm not sure, but I'm pretty positive there still
is one here, but it is not AFAIK permitted in domestic premises.


Don't ever accuse us of not making sacrifices ;)

I think the general complaint was that America makes more sacrifices,
unnecessary human ones unfortunately.

FWIW we had 110 dc here as well in the 50s, but this has universally
disappeared now.


NT