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3-Way Switches

Posted by EdF on June 19th, 2000 03:56 PM
In reply to three way light switch installation by J Goode on June 19th, 2000 04:53 AM [Go to top of thread]

1 of 1 people found this post helpful

The following, is copied from:

* For exactly two locations (say at the bottom and top of basement stairs), you
will need a pair of what are known as 3-way switches.

These are actually SPDT (Single Pole Double Throw) switches which look like
ordinary wall switches but have 3 screws instead of 2. Two of these screws
will be the same color (usually brass) while the third will be different
(darker copper or brown). They may be marked as well.

Note that a socket for a 3-way bulb for a lamp is not related to this - only
the name is similar.

Typical wiring for controlling a fixture or outlet from exactly two locations
is as follows:

Location 1 Location 2
3-way SW A 3-way SW +---------+
/o----------------o | Fixture |
Hot o-----/ o-----------| or |--------o Neutral
o----------------o Center | Outlet | Shell
B (brass) +---------+ (silver)

/o---o o---o
A 3-way switch connects either up o---/ or down o---o .
o---o o---o

As usual, the brass screw on the fixture or outlet should be connected to
the Hot side of the wiring and the silver screw to the Neutral side.

Another common variation is shown below:

Location 1 Location 2
3-way SW Rd : 3-way SW
: Bk /o------------------o
Hot o-------------------------------/ Wh : o---+
: o------------------o |
+---------+ : : |
| Fixture | : Wh Splice Bk : |
Neutral o-------| or |---------------X---------------------------+
| Outlet | : (Wirenut) :
+---------+ 14-2 14-3

Details may differ for your particular installation (like to which sides the
Hot and Neutral are connected and/or particular wire colors used).

* For more than two locations (say at 3 doors to your dining room), you will
need a combination of 3-way switches and 4-way switches. Two of the 3-way
type will be needed at the ends of the circuit (below) with 1 or more 4-way
type in between. Thus for 'n' switch locations, n-2 of the 4-way switches
will be needed.

4-way switches have 4 terminals arranged as two pairs. In one position pair
1 is connected to pair 2 straight through. In the other position, the
connections are interchanged.

Typical wiring for controlling a fixture or outlet from 3 or more locations
is as follows:

Location 1 Location 2 Location 3
3-way SW A 4-way SW A 3-way SW +---------+
/o------------o /o-----------o | Fixture |
Hot o---/ / o---------| or |---o Neutral
o------------o/ o-----------o Center | Outlet | Shell
B B (brass) +---------+ (silver)

o---o o /o
A 4-way switch connects either straight or exchange / .
o---o o/ o

This can be extended to an arbitrary number of positions.

As usual, the brass screw on the fixture or outlet should be connected to
the Hot side of the wiring and the silver screw to the Neutral side.

Note that a 4-way switch can be constructed from a DPDT (Double Pole Double
Throw) type (e.g., toggle switch) as follows:

| |
A(in) o---------------+ |
| | |
+----o o/ o-------+------o A(out)
: | |
+----o o/ o---+----------o B(out)
| | DPDT |
B(in) o---------------+ toggle |
| switch |

For low voltage (non-house wiring) or panel mount applications, this may be
easier than using actual 4-way switches (which are probably not available in
small sizes).

The 3-way switches (at least the basic white, ivory, or brown toggle type)
can be found nearly anyplace that sells common electrical devices including
hardware stores and home centers. You may have to look a little harder for
4-way switches as well as styles or colors to match your decor as these are
not as widely available. However, a decent electrical supply house should
have all of these.

The wires marked A and B (sometimes called 'travelers') may be in a single
(sheathed electrical cable) cable and should be on the screws that are both the same color.

If you do use sheathed electrical cable with a black and white wire, put black tape on the
insulation at the ends of the white wire (or paint the ends black) to
indicate that this is a Hot wire and not a Neutral. This is required by
Code but allows the use of this type of wire.

These diagrams represent one wiring arrangement. Sometimes, there are other
slight variations. For example, you might find the switches in the Neutral
instead of Hot portion of the wiring - however, this is not recommended.


Here's another link that has a good description...

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