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@REPLYADDR Jim Wilkins <muratlanne@gmail.com>
@REPLYTO 2:5075/128 Jim Wilkins
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"Bob La Londe" wrote in message news:uf4bic$3p2la$
3@dont-email.me...
In the US residential and non-industrial is usually split phase. We
have a single phase coming in, but its got a half tap at the service
transformer for 120V nominal which is what most small to medium devices
are designed to work with. The 120V device can be wire from either leg
to the half tap or neutral. It makes for some interesting conversations
with other do-it-yourselfers. In the past there were house which only
received half phase. That is their service entrance was 120V nominal
only.
I may not have the terms exactly right, but that`s the gist of it. Like
I said, it makes wiring in extra stuff interesting.
-------------------------
I remember the single drop and 60A screw-in fusebox. My father bought and
remodeled old houses as a sideline, I think because it gave him problems he
could solve with a hammer. He became pretty good at everything except 3-way
light switches. I might have helped him more if my role hadn`t been the
nail.
I would describe the US residential service as coming from a center-tapped
transformer secondary winding with the center tap defined as neutral and
grounded, thus the two ends of the secondary are 120V at 180 degrees apart,
each is 120V to neutral and 240V to the other one. In the breaker box the
connecting tabs to the two hot "phases" are interleaved such that a double
breaker connects to both for 240V, a single breaker to one for 120V, and the
single breakers above and below it are the opposite phase so hopefully the
electrician will more or less balance the loads between them as he works his
way down.
Large loads such as the kitchen stove, water heater and clothes dryer use
double breakers for 240V, wall outlets and room overhead lighting uses
single ones for 120V, with the loads connected in series unlike the British
loop that feeds from both ends. The wall outlets and switched ceiling
lighting in each room are supposed to be on different breakers so the room
can be lit with one while the other is shut off for maintenance. Back when I
learned this the wall outlet circuits were wired for 20A and the lighting
for 15A, with thinner wire. Sometimes a wall switch controls an outlet meant
for a lamp, especially if there isn`t an overhead ceiling lamp which could
cause a leak in the insulation.
There can be variations. My house has a separate meter and breaker box for
the water heater which is billed at a lower rate. The main drop is 200A for
the baseboard electric heating that was expected to be cheap nuclear in
1970. Rooftop solar uses a different meter that records power bought and
sold by the customer separately. Determining the direction of AC is actually
easy, a phone does it with voice to send and receive on a single pair of
wires.
Another difference from British practice is the fuse isn`t in the plug,
unless it`s a built-in ground fault interrupter. It protects the house
wiring, the appliance is its designers problem. Old fuse boxes were meant to
have the center contact of the screw-in fuse hot so that once you unscrewed
the fuse part way the more accessible threaded shell was safe to
accidentally touch, which it wouldn`t be with a ring main. Holders for
cylindrical glass automotive fuses that can be used for 120V should be wired
the same way, hot at the inner end.
You can identify which breaker controls an outlet without a helper by
plugging in a vacuum cleaner that vibrates the floor and can be heard from
far away.
Although house wiring is sometimes considered two phase, that term is
formally reserved for separate circuits 90 degrees apart which was Tesla`s
original sine and cosine supply that created a smoothly rotating magnetic
field to eliminate DC motor brushes. It required four distribution wires
while 3 phases at 120 degrees apart could be done more cheaply with three
and so replaced it.
Industrial schematics label the phases and the wires themselves L1, L2 and
L3 (L=Line) ,and each succeeding wire connection takes an increasing
numerical prefix, so that the wires coming from the 3 phase breaker may be
1L1, 1L2, 1L3, then 2L1, 2L2, 2L3 from a contactor to a motor, etc. The
parallel lines that look like a capacitor are normally open relay contacts
that should have their associated Control Relay (CR) indicated with a circle
for the coil. The N-like variant is a normally closed contact, normally
meaning powered off. This is called a ladder diagram because the power lines
are usually vertical and the relay contacts and coils etc drawn horizontally
between them.
-jsw
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