Gerald Brazil wrote:
>
> I would appreciate a simple explanation of typical wiring....
OK, I'll try.
> A basic 110v circuit consists of a hot wire (black), a common wire (white)
> and a ground wire (green)
That is the 3wire 110 (or 120) volt circut. Juice in on
the black hot leg, out on the white return (neutral) leg
and a green ground sepearated from both to keep
everyhing safe.
>
> A 220 v circuit consists or two hot 110v wires (one black and one red) and a
> ground wire (green).
This is the 2wire 220v no neutral with ground setup.
There are also 3wire 220v neutral and ground circut. The
neutral is used as a return or any 110 volt circuts, but
is not needed for 220 only loads.
>
> Why doesn't a 220v circuit need a common? How is the circuit completed?
>From one leg to the other leg. The current flows from
Black to Red AND from Red to Black. It's more magic
than radio. (:-) This is AC or Alternating Current.
These numbers are relative to Ground potential.
When dealing with AC electicity, one of the hardest
ideas for people to accept is the diffence between
power, neutral, and ground. Especially neutral and
ground.
++++++++++++++++++++++++++++++++++++++++++++++++++++
Caution: Long winded explanation to follow:
++++++++++++++++++++++++++++++++++++++++++++++++++++
This is for North American utilities in general and the
US in specific. See the National Elecrtic Code (NEC) for
a lot more.
Your basic household 240volt 3wire service enterance is
composed of 2 hot legs and a return. It is a
misconception to think the return leg is not a current
carrying line. The electrons flow in and the electrons
flow out, or you do not have a complete circut. Neutral
is the return and a reference point. The A phase and the
B phase are the two "hot" legs. They are 120 volts above
the return reference and 240 volts apart from each
other. They are (ususally) 180 degrees out of phase with
each other and alternating at 60 time per second. Hence
the 120/240 60cycle designator on most equipment.
_______________________ A phase 120vac to neutral 240
volts to B phase
----------------------- Neutral (Return) 0 volts to
ground
_______________________ B phase 120vac to neutral 240
volts to A phase
Don't think of the A and B as higher and lower than
neutral the way you think of +5 volts and -5 volts DC.
The analogy works just fine, but it more like A snd B
are over and under, or left asnd right of neutral. You
just can't look at one and say "This is the positive and
that is the negative".
They are 240 volts apart and they have a reference point
120 volts or midway between them. This reference is at 0
volts potential, so it makes a good point to refernce
the ground, which is the ultimate return path. What that
all means is that the return is at 0 volts, or neutral
in electrical potential. That's where the name, neutral,
comes from. This is tied to the ground at your service
panel to keep the neutral at 0 volts potential. That
bare aluminum wire coming into your house from the
utility is not a ground. It is the return line to the
utility supply transformer. The ground is supplied from
a seperate grounded conductor in your panel. The
grounded conductor is burried in the earth (ground)
outside somewhere. If you ever tour a power generating
facility ask to see thier electron sink. That's the big
honkin' ground circut. For some real fun reading, take a
look at the section of the NEC dealing with grounding
rods. Or, for that matter, on grounding in general. The
ground is not the neutral and the neutral is not the
ground. Since the Neutral IS at 0 or ground potential,
some people think there is no current flowing in it.
There is none flowing when the circut is off. But there
most certainly is current in the neutral when the circut
is on. Neutral and Ground are at the same potential only
and should never meet in a circut. They are joined in
the service panel as a reference and or safety. DO NOT
tie the neutral to ground downstream from the panel.
*************** Big time exception
*****************
In years gone by the NEC allowed ranges and dryers to
use the ground as neutral. So you had three conductor
cables for those appliances. The ground was tied to the
neutral at the j-block where the cable was connected.
Mobile home and a few local districts required a
seperate ground. 4 wire range and dryer cables became
known as "mobile home connectors". This Exception is no
longer allowed by the NEC. All range and dryer circuts
must now conform to the 4 wire standard.
********************************************
To sum it up: Loads can use a single supply leg and
neutral return. In on the supply and out on the
return.Or they can use 2 opposite supply legs with a
neutral to get 120 volts from either or both legs. In on
A or B and out on neutral. Or they can use 2 opposite
supply legs to burn 240 volts. In on A-out on B AND in
on B-out on A. All have a Ground for safety.
This is not a complete electrical explanation, but it
covers most US residental applications.
Three phase, two phase, four phase, wye vs delta, AC vs
DC. 110, 115, 120, 208, 230, 240. There are all kinds of
different systems in use here. The English use some kind
of power supply system involving toads and wizards. The
Japanese use left hand magnets so their electricity
won't work on things built in the US. In Russia they use
Imaginary Tesla Field current. Very strange stuff. This
has gone on too long but I hope it answers more question
than not.
Matt in Vancouver WA
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