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3 Way Switch Circuits
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WHILE EXTREME CARE HAS BEEN IMPLEMENTED IN THE PREPARATION OF THIS
SELF-HELP DOCUMENT, THE AWHILE EXTREME CARE HAS BEEN IMPLEMENTED IN THE
PREPARATION OF THIS SELF-HELP DOCUMENT, THE AUTHOR AND/OR PROVIDERS OF
THIS DOCUMENT ASSUMES NO RESPONSIBILITY FOR ERRORS OR OMISSIONS, NOR IS
ANY LIABILITY ASSUMED FROM THE USE OF THE INFORMATION, CONTAINED IN THIS
DOCUMENT, BY THE AUTHOR and / OR PROVIDER.
You will need...
1. A 4 wire cable that is routed between switch box 1 and switch
box 2 - these wire cables comes with a black / red / blue (or
white striped) / white wire plus the bare equipment grounding
wire.
2. A 2 wire cable that is routed between switch box 1 and the
fixture box - this wire cable comes with a black / white wire
plus the bare equipment grounding wire.
3. A circuit power supply source wire cable that is feed to the
switch 1 box.
4. Insulated wire nuts to connect / join wire together, variety
of sizes out there so make sure you obtain the correct size.
5. Wire staples, to affix the wire cables to wall studs as
needed. Wire cable must be secured within 6 inches of entering
the electrical box.
6. Wire cable / wire strippers.
7. Screwdrivers as required.
Holes drilled to feed wires through studs must be 1 1/4" from
edge of stud, in instances where the wire cable is closer then
the edge of stud must have a 1/16-in. thick protective metal
plate over the area where the cable is being feed through (may
want to notch the stud so that that the protective plate does
not create a bump on the drywall). Also read the article called
' Wire
Routing Basics'
Wire cables entering the electrical box - secure the cable clamp
at the box snug enough that the cable cannot come out but not
too tight as to pinch the cable and break through the insulated
cover of the cable.
You must have at least 6 inch length of wire inside the
electrical box, it can be a bit more but not less, it can fail
an inspection if the length of each wire is less than 6 inches.
Also read the article called
'Box Fill Calculations' as there is a
limit on how many wires are allowed for a certain size
electrical box.
STEP 1 - Make
certain that the power supply cable is dead - turn off the
electrical breaker at the service panel. Make certain that
everyone in the house is aware of what you are doing so that
they do not get the notion to reset the breaker when another
light in the home is not working.
STEP 2 - Make
the box openings (if a existing home)
STEP 3 - Feed / Route the wire cables.
STEP 4 -Mount
/ Install the Electrical Boxes (make sure the electrical boxes
are secured as some fixtures are heavy and may require
additional support) [The electrical box should not extend beyond
the edge of the finished wall or ceiling so that the fixture can
mount flush to the ceiling and the wall switch cover will mount
flush - but it also should not be recessed too far into the wall
or ceiling]; then feed the wire cables into the electrical
boxes. Sometimes because of tight openings in existing homes,
the wire cable may to be feed into the electrical box then the
box put in position and secured.
STEP 5 -
Connect the wires...
Connections
Instructions:
(as depicted in the diagrams above)
At the Fixture box...
One cable entering this box coming from switch 1.
* a) connect the white wire coming switch 1 to the grounded
conductor (neutral) of fixture - if screw type connections then
connect to the silver color screw
* c) connect the black wire coming from switch 1 to the switched
ungrounded conductor (hot) of fixture - if screw type connections
then connect to the brass color screw.
* d) please see under important notes in regards to the equipment
grounding conductor (bare wire).
At switch 1 box...
Three cables entering this box, one is coming from the fixture, one
cable coming from switch 2, and the 'circuit power supply cable'.
* a) using an insulated wire nut connect / join the white wire
coming from fixture + the white wire coming from switch 2 + the
white wire coming from 'circuit power supply cable'.
* b) connect the black wire coming from fixture to the common screw
of switch 1.
* c) using an insulated wire nut connect / join the black wire
coming from switch 2 + the black wire from 'circuit power supply
cable'.
* d) connect the red wire coming from switch 2 to the one of the
remaining main screws of switch 1.
* e) connect the blue wire coming from switch 2 to the last
remaining main screw of switch 1.
* f) please see under important notes in regards to the equipment
grounding conductor (bare wire).
At switch 2 box...
One cables entering this box coming from switch 1.
* a) connect the black wire coming from switch 1 to the common screw
of switch 2.
* b) connect the blue wire coming from switch1 to one of the
remaining main screws of switch 2.
* c) connect the red wire coming from switch 1 to one of the
last remaining main screws of switch 2.
* d) using an insulated wire nut cap off the white wire coming from
switch 1.
* e) please see under important notes in regards to the equipment
grounding conductor (bare wire).
Important Notes:
By electrical codes you MUST have at least 6 inches of wire in the
electrical box itself, and also the wire must be able to reach at
least 3 inches outside the box, it can fail an electrical inspection
if the required min. wire length is not met. You may have the wires
a bit longer (within reason) but they cannot be shorter. Also see
the note on box fill further down in this article.
If the fixture has screw type connectors, the switched ungrounded
conductor (hot) is connected to the brass color screw, and the
grounded conductor (neutral) is connected to the silver color screw.
If it has black and white wires coming from fixture, then just
connect black to black and white to white. Use wire nuts of the
correct size to join wires together.
The wire cable running between switch 1 and switch 2 has 4 wires in
it - black / red / blue / white (plus the bare equipment grounding
wire)
What is not shown in the drawings to avoid confusion, is that each
wire cable also has a bare equipment grounding wire included. This
wire is connected to a equipment grounding screw in each electrical
box (if the box is metal), joined either through the equipment
grounding screws in the box itself or via a wire nut to the bare
wire of the next cable entering / exiting the box, it is also
connected to any equipment grounding screw (if there is one) on the
switch itself, as well as any equipment grounding screw at the
fixture (green wires that attach to the fixture are grounds). Now if
using a plastic box, it is made of a material that is non
conductive, however some plastic boxes have a metal strip inside
that can still be used to connect equipment grounding wires, in the
event that it does not then use wire nuts to join the bare equipment
grounding wires together. The equipment grounding wire (bare in most
cables) must be electrical conductively joined throughout the
circuit. Green wires are also equipment grounding conductors.
At the switch itself there are 3 main electrical screws, one of
these 3 screws is distinctly different in color (perhaps darker)
than the other 2. This screw connection is called the common screw.
It is very important that in order for the 2 switches to work as
they are intended to that the correct wire is attached to the common
screw. Basically as depicted in the drawings one switch has the
ungrounded conductor (hot) from the 'circuit power supply' cable
attached to the common screw, where the other switch had the
switched ungrounded conductor (hot) feed to the light fixture
itself.
Please also note that there are a variety of manufactures out there
that make 3 way switches so it is possible that the switch you buy
may have the common screw located in a different spot or side of the
switch then depicted in the drawings in this article, just make sure
that the wire depicted to go to the common screw of each of the
switches is actually connected to the common screw of the 3 way
switch you bought. The other 2 wires going between the remaining
screws of one switch to the other switch does not matter as long as
one wire of the 2 remaining wires go on each of the remaining 2
screws of the screw.
If there is an equipment grounding screw on the 3 way switch it may
be green in color and be separated away from the main connections of
the switch and likely part of the metal frame that is also part of
the mounting structure of the switch.
Extensions to this Switch
circuit...
Be Aware that there is a limit by code on how many wires can be in a
given size electrical box, when adding more wires to the same box
you may have to install a larger and / or deeper box to allow space
for more wires coming and out of the box.
Here is an article / explanation in regards to box fill calculations
' Box
Fill Calculation'
The instructions here are based on the fact that the circuit has
already been wired to the configuration shown in this article and we
are now making the wiring changes for onward power
From the switch locations.....
Switch 1 options...
Option 1: Onward Always On
Circuit Power...
(showing bellow the switch 1 portion of the circuit)
Not shown in the diagram but the onward cable
also has a bare wire (equipment grounding conductor) that also must
be connected to all the other bare wires at the switch electrical
box.
Connection Instructions for
onward cable (always on state)
* a) Using an insulated wire nut, attach / join - the white wire of
onward cable + the white wire coming from the 'circuit power supply
cable' + the white wire coming from switch 2 + the white wire coming
from fixture.
* b) Using an insulated wire nut, attach / join - the black wire of
onward cable + black wire of 'circuit power supply cable' + black
wire coming from switch 2.
Identification of wires in onward
cable....
Black - Ungrounded conductor (hot - always on)
White - Grounded conductor (neutral)
*************
Option 2: Onward switched
power...
(example more than one light fixture controlled by the same 3 way
switches)
(showing bellow the switch portion of the circuit)
Not shown in the diagram but the onward cable
also has a bare wire (equipment grounding conductor) that also must
be connected to all the other bare wires at the switch electrical
box.
Connection Instructions for
onward cable (switched)
* a) Using an insulated wire nut, attach / join - the white wire of
onward cable + the white wire coming from switch 2 + the white wire
coming from 'circuit power supply cable' + the white wire coming
from fixture.
* b) Using an insulated wire nut, attach / join - the black wire of
onward cable + the black wire connected to common screw of switch 1
+ the black wire coming from fixture.
Identification of wires in onward
cable....
Black - Switched Ungrounded conductor (hot - switched)
White - Grounded conductor (neutral)
****************
Option 3: Onward 'always on' &
switched power...
(showing bellow the switch portion of the circuit)
Not shown in the diagram but the onward cable
also has a bare wire (equipment grounding conductor) that also must
be connected to all the other bare wires at the switch electrical
box.
Connection Instructions for
onward cable ('always on' & switched)
* a) Using an insulated wire nut, attach / join - the white wire of
onward cable + the white wire from 'circuit power supply cable' +
the white wire coming from switch 2 + the white wire coming from
fixture.
* b) Using an insulated wire nut, attach / join - the black wire of
onward cable + the black wire connected to common screw of switch 1
+ the black wire coming from fixture.
* c) Using an insulated wire nut, attach / join - the red wire of
onward cable + the black wire coming from the 'circuit power supply
cable' + the black wire coming from switch 2.
Identification of wires in onward
cable....
Black - Switched Ungrounded conductor (hot - switched)
Red - Ungrounded conductor (hot - always on)
White - Grounded conductor (neutral)
***************
Switch 2 Onward Options...
(only onward 'always on' power is available from the switch 2
location)
Not shown in the diagram but the onward cable
also has a bare wire (equipment grounding conductor) that also must
be connected to all the other bare wires at the switch electrical
box.
Connection Instructions for
onward cable (always on)
* a) Using an insulated wire nut, attach / join - the white wire of
onward cable + the white wire coming from switch 1.
* b) Using an insulated wire nut, attach / join - the black wire of
onward cable + the black wire connected to common screw of switch 2
+ the black wire coming switch 1.
Identification of wires in onward
cable....
Black - Ungrounded conductor (hot - always on)
White - Grounded conductor (neutral)
****************
From the fixture location...
At the fixture location only switched onward power is available.
(showing bellow the fixture portion of the circuit)
Not shown in the diagram but the onward cable
also has a bare wire (equipment grounding conductor) that also must
be connected to all the other bare wires at the fixture electrical
box.
Connection Instructions for
onward cable (switched)
* a) Using an insulated wire nut, attach / join - the white wire of
onward cable + the white wire coming from switch 1 + the white wire
connected to the grounded conductor (neutral) of fixture - if screw
type connections then connect to silver color screw.
* b) Using an insulated wire nut, attach / join - the black wire of
onward cable + the black wire coming from switch 1 + the black wire
connected to the switched ungrounded conductor of fixture (shown as
black in diagram) - if screw type connections then connect to brass
color screw.
Identification of wires in onward
cable....
Black - Switched Ungrounded conductor (hot - switched)
White - Grounded conductor (neutral)
Foreign Users:
The colors of the wires depicted are based on the standards and code
requirements / configuration in the United States and Canada. If you
are viewing this site from a foreign country, your wiring standards
and color of wires may be different but the principal and sequence
of wiring will still remain the same. Therefore the information in
this article may still be of use to you regardless of what country
you may be in. Just translate the colors used here to the color of
wires used in your country in regards to ungrounded (hot) conductors
/ grounded conductors (neutral) and equipment grounding conductors
as well know applicable code requirements in your country.
By: Donald Kerr
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