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When
you shop for devices like switches and outlets, there are several different types
to wade through. Make sure to get the device that works properly with the circuit. The type of switch you install is determined by the circuit's wiring scheme. Outlets are pretty standard, but GFCIs are required in some rooms and box size is another thing to consider.
Sizing Junction Boxes
Installing
an undersized box is probably the most common wiring mistake for do-it-yourselfers.
When in doubt, it's usually best to use a larger box. If
you're not sure about box size requirements, remember to ask your electrical inspector
when submitting diagrams. Here's one way to calculate minimum box size: The result is the minimum allowable volume the box should be. Volumes are usually stamped into the back of the box on the inside.
These
buttons allow you to check the GFCI monthly to see if it's still working properly.
Push in the black "Test" button to kill power to that circuit. Restore
power by pushing the red "Reset" button. A
GFCI also monitors the current being used by anything plugged into it. Normally,
a balance of current passes through the GFCI. If a misdirection of current, called a "fault to ground," the GFCI senses it and shuts down almost instantly -- which can prevent potentially hazardous shocks.
The
bottom brass and silver set -- marked "Line" -- is for incoming wires.
The top set -- marked "Load" -- is for wires going to other protected outlets.
The
GFCI also has a green "ground" screw on the bottom. That's where the bare copper
ground wire connects and provides a path for dangerous current to be safely diverted.
The
neutral wires tie together separately and the ground wires tie together separately
in the box. Many
new switches include a ground screw; others may not have one. If you have the
choice, get a switch with a ground screw terminal. That's where the bare copper
or green wire connects. When a switch is at the end of a circuit (one incoming cable), the neutral also becomes a hot lead and connects to a terminal. This type of wiring scheme is often called a switch loop.
A
three-way switch has three screws. One screw is colored darker than the other
two. It's called the "Common" terminal. The other two screws are called
"Traveler" terminals. You
can wire two three-way switches and a light in a few different ways. It all depends
where the light is located: before, between or after the switches. What
we describe is not how all three-way switches are wired. But the following will
give you an idea of how they're connected. For
simplicity, let's say the light is after both switches. The first box has
two cables: one 14-2 incoming from a power source, and one 14-3 outbound to the
second box. The
second box has that incoming 14-3 cable and an outbound 14-2 cable to the light.
In
each box, twist all the ground wires together (add a pigtail in each metal box).
Screw on a wire connector (and fasten the pigtail to the back of the metal box). Connect the two neutral leads in each box with wire connectors.
In
the second box, hook up the incoming (14-3) hot leads to the switch's travelers
screws. Finally, hook up the outbound (14-2) hot lead going to the light to the "Common" screw. That completes wiring the switches. Complete the circuit by hooking up the light to the neutral, hot and ground leads. | |||
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More How-To Information: | |||
Most switches and outlets are installed after mechanical rough-ins, drywall and paint are completed. 
All switches and outlets (receptacles) need a properly-sized junction (electrical)
box. For example, a 2" x 3" box with 3 wires (14 gauge) should be 2 1/2" deep.
The same box with 5 wires must be 3 1/2" deep. 
1. Count the number of wires for the box. Don't count outlet/switch
pigtails and count all ground wires as one.
A GFCI (Ground Fault Circuit Interrupter, also GFI) is an outlet designed to prevent
electrical shock. It's a little bigger than a normal outlet and has two buttons
on the front. 
On
the back side of a standard GFCI are four (two sets) terminal screws -- two brass
"hot" screws and two silver "neutral" screws. 
A single-pole switch has two brass screw terminals. Both are hot leads for one
incoming and one outgoing line. Those are all the wires that connect to the switch.
Three-way switches can control one light from two different places. Like switches
that operate a light from both the top and bottom of a staircase. 
In
the first box, connect the incoming (14-2) hot lead to the switch's "Common"
terminal. Connect the outbound (14-3) leads to the two "Traveler" screws.
In this case, the traveler leads can be hooked to either terminal.