At the home, the three wires from
the pole/green box transformer are connected through a wattmeter and then enter
a main service panel that is grounded to a long copper rod driven into the
ground or to the steel in a home's foundation. The A-phase and B-phase wires
that enter the main panel are connected through a main disconnect breaker,
while the neutral wire is connected to a terminal referred to as the neutral
bar or neutral bus. A ground bar also may be present within the main service
panel. The ground bar is connected to the grounding rod or to the foundation's
steel supports. Within main service panels, the neutral bar and the ground bar
are connected together (they act as one).
However, within subpanels (service
panels that get their power from the main service panel but which are located
some distance from the main service panel), the neutral and ground bars are not
joined together. Instead, the subpanel's ground bar receives a ground wire from
the main service panel. Often the metal conduit that is used to transport the
wires from the main service panel to the subpanel is used as the "ground
wire." However, for certain critical applications (e.g., computer and
life-support systems), the ground wire probably will be included within the
conduit. Also, if a subpanel is not located in the same building as the main
panel, a new ground rod typically is used to ground the subpanel. Note that
different regions within the United States may use different wiring protocols.
Within the main service panel, there
are typically two bus bars into which circuit breaker modules are inserted. One
of these bus bars is connected to the A-phase wire; the other bus bar is
connected to the B-phase wire. To power a group of 120-V loads (e.g., upstairs
lights and 120-V outlets), you throw the main breaker to the off position and
then insert a single-pole breaker into one of the bus bars. (You can choose
either the A-phase bus bar or the B-phase bus bar. The choice of which bus bar
you use only becomes important when it comes to balancing the overall load-more
on that in a second.) Next, you take a 120-V three-wire cable and connect the
cable's black (hot) wire to the breaker, connect the cable's white (neutral)
wire to the neutral bar, and connect the cable's ground wire (green or bare) to
the ground bar. You then run the cable to where the 120-V loads are located,
connect the hot and neutral wires across the load, and fasten the ground wire
to the case of the load (typically a ground screw is supplied on an outlet
mounting or light figure for this purpose).
To power other 120-V loads that use
their own breakers, you basically do the same thing you did in the last setup.
However, to maximize the capacity of the main panel (or subpanel) to supply as
much current as possible without overloading the main circuit breaker in the
process, it is important to balance the number of loads connected to the
A-phase breakers with the number of loads connected to the B-phase breakers.
This is referred to as balancing the
load. Now, if you want to supply power to 240-V appliances (e.g., ovens,
washers, etc.), you insert a double-pole breaker between the A-phase and
B-phase bus bars in the main panel (or subpanel). Next, you take a 240-V
three-wire cable and attach one of its hot wires to the A-phase terminal of the
breaker and attach its other hot wire to the B-phase terminal of the breaker.
The ground wire (green or bare) is connected to the ground bar. You then run
the cable to where the 240-V loads are located and attach the wires to the
corresponding terminals of the load (typically within a 240-V outlet). Also,
120-V/240-V appliances are wired in a similar manner, except you use a four
wire cable that contains an additional neutral (white) wire that is joined at
the neutral bar within the main panel (or subpanel). (As a practical note, you
could use a four wire 120-V/240-V cable instead of a 240-V three-wire cable for
240-V applications- you would just leave the neutral wire alone in this case.)
As a note of caution, do not attempt
home wiring unless you are sure of your abilities. If you feel that you are
capable, just make sure to flip the main breaker off before you start work
within the main service panel. When working on light fixtures, switches, and
outlets that are connected to an individual breaker, tag that breaker with tape
so that you do not mistakenly flip the wrong breaker when you go back to test
your connections.
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At
the home, the three wires from the pole/green box transformer are
connected through a wattmeter and then enter a main service panel that
is grounded to a long copper rod driven into the ground or to the steel
in a home's foundation. The A-phase and B-phase wires that enter the
main panel are connected through a main disconnect breaker, while the
neutral wire is connected to a terminal referred to as the neutral bar
or neutral bus. A ground bar also may be present within the main service
panel. The ground bar is connected to the grounding rod or to the
foundation's steel supports. Within main service panels, the neutral bar
and the ground bar are connected together (they act as one).
However,
within subpanels (service panels that get their power from the main
service panel but which are located some distance from the main service
panel), the neutral and ground bars are not joined together. Instead,
the subpanel's ground bar receives a ground wire from the main service
panel. Often the metal conduit that is used to transport the wires from
the main service panel to the subpanel is used as the "ground wire."
However, for certain critical applications (e.g., computer and
life-support systems), the ground wire probably will be included within
the conduit. Also, if a subpanel is not located in the same building as
the main panel, a new ground rod typically is used to ground the
subpanel. Note that different regions within the United States may use
different wiring protocols.
Within the main service panel, there
are typically two bus bars into which circuit breaker modules are
inserted. One of these bus bars is connected to the A-phase wire; the
other bus bar is connected to the B-phase wire. To power a group of
120-V loads (e.g., upstairs lights and 120-V outlets), you throw the
main breaker to the off position and then insert a single-pole breaker
into one of the bus bars. (You can choose either the A-phase bus bar or
the B-phase bus bar. The choice of which bus bar you use only becomes
important when it comes to balancing the overall load-more on that in a
second.) Next, you take a 120-V three-wire cable and connect the cable's
black (hot) wire to the breaker, connect the cable's white (neutral)
wire to the neutral bar, and connect the cable's ground wire (green or
bare) to the ground bar. You then run the cable to where the 120-V loads
are located, connect the hot and neutral wires across the load, and
fasten the ground wire to the case of the load (typically a ground screw
is supplied on an outlet mounting or light figure for this purpose).
To
power other 120-V loads that use their own breakers, you basically do
the same thing you did in the last setup. However, to maximize the
capacity of the main panel (or subpanel) to supply as much current as
possible without overloading the main circuit breaker in the process, it
is important to balance the number of loads connected to the A-phase
breakers with the number of loads connected to the B-phase breakers.
This
is referred to as balancing the load. Now, if you want to supply power
to 240-V appliances (e.g., ovens, washers, etc.), you insert a
double-pole breaker between the A-phase and B-phase bus bars in the main
panel (or subpanel). Next, you take a 240-V three-wire cable and attach
one of its hot wires to the A-phase terminal of the breaker and attach
its other hot wire to the B-phase terminal of the breaker. The ground
wire (green or bare) is connected to the ground bar. You then run the
cable to where the 240-V loads are located and attach the wires to the
corresponding terminals of the load (typically within a 240-V outlet).
Also, 120-V/240-V appliances are wired in a similar manner, except you
use a four wire cable that contains an additional neutral (white) wire
that is joined at the neutral bar within the main panel (or subpanel).
(As a practical note, you could use a four wire 120-V/240-V cable
instead of a 240-V three-wire cable for 240-V applications- you would
just leave the neutral wire alone in this case.)
As a note of
caution, do not attempt home wiring unless you are sure of your
abilities. If you feel that you are capable, just make sure to flip the
main breaker off before you start work within the main service panel.
When working on light fixtures, switches, and outlets that are connected
to an individual breaker, tag that breaker with tape so that you do not
mistakenly flip the wrong breaker when you go back to test your
connections.
Article Source:
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Article Source: http://EzineArticles.com/9767196
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