Post by Tony PolsonOh my God! And we think MRSA is serious ...
;-)
In America you could buy cables with a plug on each end. I have an old
Speed Graphic press camera with a Graflite flashgun, the sort that
takes lightbulb sized flashbulbs (which I've still got a large stock
of. There are five connection on the battery case, shutter, battery,
remote, solenoid and extension, and all are standard 2 pin (Nema 1-15)
mains type sockets, so to connect up multiple flashes you need a cable
with a mains plug on each end; Graflex used to see these.
You can get various other electrical horrors over there; their mains
is a 240V centre-tapped three wire system, like the 110V we use on
building sites, but twice the Voltage. Normal small appliences are
connected between neutral which is white, and hot (live) which is
black. Ground (earth) is green. Half of the 120V sockets in a house
will be connected to one side of the supply, and half to the other.
Large things like Cookers are connected across the two lives to give
the full 240V, with the second live being red, though sometimes a
neutral is used as well, so small loads like oven timers can run off
120V. The normal 120V 3 pin plug is a Nema 5-15, which has the hot and
neutral pins vertical, but there is a 240V one, the Nema 6-20, which is
similar, but which has the pins horizontal. I've seen a cable on sale
with a 240V plug on one end, and a 120V socket on the other.
These sockets are rated at 15 Amps, but there are 20A versions, the
Nema 5-20 and 6-20, which have one horizontal and one vertical pin, I
think it's the live pin which is the opposite way round to it would be
in a 15A version. In the USA 20A sockets have a 'T' shaped slit, so
they can accept both 15A and 20A plugs, but in Canada this is not
allowed, so a 15A plug cannot be used in a 20A socket. Then there are
the 30 an 50 Amp versions, with all sorts of odd pin arrangements.
Unless you can remember the dozens of slightly different Nema
configurations it's not obvious what a socket is; if it's got three
pins it could be single phase hot, neutral and ground or two hots and a
ground or three phase ungrounded. Four pins could be two hots, neutral
and ground or three phase plus ground. To confuse things even more
what we call the earth they call the *grounding* conductor, and what we
call the neutral they often call the *grounded* conductor. No
opportunity for confusion there, obviously. Sometimes a single
conductor us use to serve both purposes, though this is now uncommon,
and I believe is being completely phased out.
There are some other wonderful things you can buy over there, like
adaters to plug three pin plugs into two pin sockets, they usually have
a thin metal tab with a hole in which you are supposed to earth by
putting it under one of the screws in the socket, but they never seem
to be in the right place to be able to do this. Adapters to fit plugs
into light bulb sockets, long banned here, are readily available there.
One really good example I saw I wish I had bought a sample of to
bring home. You unscrew your light bulb, and you can then screw in the
adapter. The bottom of the adapter has a standard Edison screw socket,
so you can screw the light bulb back in there. In both the left and
right sides of the adapter there is a standard 15A 120V mains socket.
Of course, since this thing screws into a light bulb socket here's no
earth. That's fine for two pin appliences, but what if you need to
plug in something with a three pin plug? No problem, there's a hole
moulded into the plastic to give the ground pin somewhere to go! The
quality of this thing was so bad that it actually distorted in my hand
as I picked it up to look at.
Then thre's American three phase; where can we start with this? Well,
it can be Wye (star) or delta; or something called open delta, I
haven't managed to work out what that is yet. 240V delta systems are
quite common, often with one of the windings centre-tapped to ground to
supply the usual 120-0-120 single phase arrangement. Since it is the
centre of one side of the delta which is grounded, the opposite point
will be at 208V. This tends to be known as the 'high leg' or
'stinger', so in a distribution board, one third of the wires will be
at a higher Voltage from ground than the others. These tend to be
identified by marking them with orange tape. Then there are corner
crounded delta systems, and ungrounded ones, and something like a dozen
different odd Voltages, 277V, for example. That's emough, I can't take
any more of this!