Re: Internal wiring of USA v UK mains plug

[John Larkin]

I've heard of those, I don't recall ever actually seeing a 240V window AC
unit though. AC in general is very rare around here and if people have it,
it's normally central. Perhaps 0.1% of the houses have vertical casement
windows that an AC unit will fit in, I suppose that would explain it.

240-volt, single-phase plugin window-mount a/c units are very common
in the US south, in older homes. They are nearly essential to
survival.

John

 

[John Fields]

Good one John, but what took you so long?

 

[John Larkin]

Boy I sure have, things got really cheap in the late 70s, about half the
outlets in my 1979 house were bad, of course they also were the cheap
bargain bin home center junk. You can get a pretty good outlet that will
last a long time for about 2 bucks, or you can get a really crappy one that
will wear out for about 75 cents. Guess which goes into most cookie cutter
houses they're building these days?

I've been in this house for about 14 years with zero electrical
problems. The British stuff is no doubt more reliable, but both are
plenty good enough; the US stuff works and is a tiny overall hazard to
life compared to other things.

John

 

[John Larkin]

I can't comment on that, since I don't have reliable data, but simply asked,
what about the other plain? And it also is much easier to have a slotted pipe
type receptacle, with a steel tape spring surrounding it to guarantee,
constant, long-term contact pressure for a round, mechanically sound, 5mm pin,
which gives solid, equal contact all around its circumference.

I think it has a good reason that the later added third ground pin for the US
system isn't of flat spade shape anymore, but strangely a round one now with,
who would have thought it, 5mm like in the Schuko system as well ;-)

All three pins on the other end of an IEC power cord are flat blades.

John

 

[John Larkin]

You're not saying there is 100 year old wiring still in use?

My previous house, a Victorian built in 1892, had gas pipes leading to
all the lighting fixtures, capped off, and exposed knob-and-tube
wiring in the attic. Junctions were twisted and taped, hanging in
mid-air. I assume the original wiring was intended for lighting, and
over the years, as more loads were added, it became less suited. I had
a few joints open up, and eventually rewired it with Romex, with all
joints inside proper metal junction boxes. There's still a lot of
ancient fabric-insulated, twisted-junction knob-and-tube stuff around.

http://www.oldhouseweb.com/stories/Detailed/10327.shtml

http://www.knobandtubewiring.com/knob and tube.gif

It's common to see a fuse box, designed for 5 or 10-amp screw-in
fuses, to be full of 30's.


Around here, knob-and-tube was succeded by mandatory rigid steel
conduit and later, roughly 1960 maybe, Romex. Commercial buildings
must still use conduit, rigid metal pipe or the flexible MX stuff.
There is no requirement that old construction be upgraded, unless a
major remodel is done.


John

 

[jakdedert]

There are also outlets used for room air conditioners. I have a 120V
15/20A outlet by one window downstairs and a 240V 20A (IIRC) outlet
for the thru-the-wall AC. Stoves and clothes dryers may also have
either a three pin ungrounded or four pin grounded outlet.

In addition, there are at least a couple of different 240v outlets used
for clothes dryers. In fact that's one appliance commonly supplied
'minus' a cord...the appropriate one being fitted at time of installation.

jak

 

[jakdedert]

They are about the same as the IEC connector on the other end of most
power cords. No big deal.

Physically, perhaps, but inasmuch as the IEC connector is a temporary
connection (and user replaceable), and the Edison is supposed to be
permanent...not the same at all.

I think that the number of deaths from US-style outlets is minute.
Electrocution and electrical fires result mostly from bad/old house
wiring and faulty appliances.

Electrocution rarely if ever results from a faulty connection, although
the Edison plug design is prone to tampering and accidental shock hazard
by children. It's possible to partially insert the plug and little
fingers to get on the exposed--but energized--prongs.

Germany runs about 1 PPM annual risk of death from electrocution, with
the USA closer to 2 PPM. That's not a lot of risk. I recall reading
that the majority of electrocutions in the US are on construction
sites, things like machines and ladders hitting high-voltage lines.

Perhaps you're referring back to an earlier part of the thread, but
there is nothing in this post about electrocution. Rereading the above,
it is about the propensity of the common Edison socket to wear out and
cause intermittent connections.

FIRE hazard, not electrocution.....

Really, cars are hundreds of times more dangerous than electricity,
and cigarettes 10x again. If Europeans want to save lives, they should
discourage smoking.

Those hazards are being addressed. What does the above have to do with
the shortcomings of American Edison sockets?

jak

 

[[email protected]]

In the US, we know better than to do stupid crap like plugging in live
equipment.

Good Luck!
Rich

Are you really saying no-one ever unplugs things withoutout turning
them off first? I really doubt it.


NT

 

[Gary Tait]

[email protected] wrote in @n2g2000hse.googlegroups.com:

Are you really saying no-one ever unplugs things withoutout turning
them off first? I really doubt it.

Some equipment simply has no off switch..

 

[James Sweet]

[email protected] wrote in @n2g2000hse.googlegroups.com:


Some equipment simply has no off switch..

Who cares? I unplug and plug in items that are turned on all the time, worst
case you get a little spark, it doesn't cause any problems. It's not hot
enough to pit the plug prongs or contacts.

 

[Tam/WB2TT]

They are about the same as the IEC connector on the other end of most
power cords. No big deal.

I think that the number of deaths from US-style outlets is minute.
Electrocution and electrical fires result mostly from bad/old house
wiring and faulty appliances.

Germany runs about 1 PPM annual risk of death from electrocution, with
the USA closer to 2 PPM. That's not a lot of risk. I recall reading
that the majority of electrocutions in the US are on construction
sites, things like machines and ladders hitting high-voltage lines.

I really can't recall reading about anybody being electrocuted inside a
house. I do recall a case involving a swimming pool. Typically, someone
manages to get across a 2.4 KV line; there one of three things that will
happens: 1 - you get bad burns and live, 2 - you fall off the ladder and die
of the fall, 3 - you die of the electrocution. Probably the worst case is
somebody holding on to an aluminum ladder with both hands that comes in
contact with an electric wire. Your chances of being electrocuted due to
casual contact with a 120 line are pretty much nil.

Tam

 

[John Larkin]

Physically, perhaps, but inasmuch as the IEC connector is a temporary
connection (and user replaceable), and the Edison is supposed to be
permanent...not the same at all.

Electrocution rarely if ever results from a faulty connection, although
the Edison plug design is prone to tampering and accidental shock hazard
by children. It's possible to partially insert the plug and little
fingers to get on the exposed--but energized--prongs.

That might generate a tickle. The geometry is very unlikely to be
lethal. Chewing on cords, especially by pets, is a more serious
hazard, and 240 is a lot worse than 120 there.

Perhaps you're referring back to an earlier part of the thread, but
there is nothing in this post about electrocution. Rereading the above,
it is about the propensity of the common Edison socket to wear out and
cause intermittent connections.

FIRE hazard, not electrocution.....

Those hazards are being addressed. What does the above have to do with
the shortcomings of American Edison sockets?

I don't have access to the statistics, but I really doubt that the
American plug/socket combo is a significant source of fires.


John

 

[Robert Latest]

["Followup-To:" header set to sci.electronics.design.]

If Europeans want to save lives, they should
discourage smoking.

All European countries want to, with the quite influential exception of
Germany. I seem to remember having read that Germany was the world's biggest
cigarette exporter. That and some EUR 14b annual tobacco tax income say
progress is going to be slow, but there is some.

robert

 

[b]

Who cares? I unplug and plug in items that are turned on all the time, worst
case you get a little spark, it doesn't cause any problems. It's not hot
enough to pit the plug prongs or contacts.

may not seem so at first, but this will damage the contacts and lead
to the formation of carbonised areas. And more noticeable stateside
what with the limited 'actual' contact area between the US plugs and
sockets - I would avoid plugging in or removing plugs of live
equipment for reliability reasons.

-B

 

[[email protected]]

Who cares? I unplug and plug in items that are turned on all the time, worst
case you get a little spark, it doesn't cause any problems. It's not hot
enough to pit the plug prongs or contacts.

Its well known that repeated small sparks make a total mess of the
contact surface. This was one of the problems of our olf round pin
system half a century ago.


NT

 

[[email protected]]

lethal. Chewing on cords, especially by pets, is a more serious
hazard, and 240 is a lot worse than 120 there.

Dont think I've ever seen pet chewed cords here, maybe different
checmicals get used in the plastic or something.

120 0r 240 would kill either way.

I don't have access to the statistics, but I really doubt that the
American plug/socket combo is a significant source of fires.

John

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=148498


NT

 

[John Larkin]

Dont think I've ever seen pet chewed cords here, maybe different
checmicals get used in the plastic or something.

My cats love our Apple products, which have soft vinyl cords. They
won't touch my Intel-based systems. Smart cats, no?

120 0r 240 would kill either way.

240 is much more likely to kill.

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=148498

It's not clear that the paper is relevant, and I'm not going to buy it
to find out. Having designed equipment with, likely, a few million
1-amp-and-up connections, and no meltdowns much less fires so far, I'm
skeptical. And a US electrical plug is hardly "a current-carrying
loose copper wire connection."


John

 

[Dave Plowman (News)]

Its well known that repeated small sparks make a total mess of the
contact surface. This was one of the problems of our olf round pin
system half a century ago.

You'd have to explain that. Most of the old round pin sockets were
switched - unswitched was a short lived fashion with 13 amp stuff. At
least in my experience.

The old round pin sockets were far more likely to be overloaded, though.

 

[jakdedert]

If an earth ground is not available, a GFI outlet should be installed at
the beginning of the run and 3 prong outlets along the rest of the run.

The GFI will trip if a ground fault is present.

The outlets should be marked to indicate that a GFI is installed and that
no earth ground is present.

I believe that this is much safer than using 2 prong outlets and meets
code.

Yes it is, and I'm perfectly aware of the fact. OTOH, replacing with
original equipment is far more responsible than doing what most people
do: replacing with a three prong outlet and either leaving the ground to
float...or worse yet, bonding ground to neutral.

Eventually, all those two-blade outlets will be rewired properly, with
new circuits added. I've done about 25% of the house so far, but it's
slow going....

jak

jak

 

[Spurious Response]

Its well known that repeated small sparks make a total mess of the
contact surface. This was one of the problems of our olf round pin
system half a century ago.

It is also well known that the properly designed flat blade has a nose
which has sharp enough corners to be the spark point for any arcs. That
means they will all begin or end along those edges, and along the "lead
in" faces of the receptacle. This means that the swept surfaces that
make up the "contact area" of the blades and socket terminals during use
will always be in fine shape.

Our plugs are designed to handle tens of thousands of "hot insertions"
like this. It has to handle some specific number at full rated current
as well. It is part of the design spec for the outlet. This is also why
the ground pin on 3 wire setups is slightly longer. It "makes" contact
before the other "pins" (blades).