3 Way Switch Wiring
Power Source at Fixture
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You will need...
1. A 3 wire cable that is routed between switch box 1 and switch box
2 - these wire cables comes with a black / red / 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
fixture 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 at least 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 (on our sister website 'Wiring Done
Right' - will open in new window / tab) 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 (on our sister website 'Wiring Done Right' - will open in new
window / tab) '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...
Connection Instructions:
At the Fixture box...
Two cables entering this box, one is the circuit power supply cable, the
other cable (wire cable # 1) coming from switch 1.
*
a) using an insulated wire nut connect / join the black wire from the 'circuit power supply cable'
+ white wire of the cable coming from switch 1.
*
b) connect the white wire from 'circuit power supply' cable to the grounded
conductor (neutral) of fixture - if screw connections at fixture connect
to the silver color screw.
* c) connect the black wire coming from switch 1 to the switched
ungrounded conductor (hot) of the fixture - if screw connections at
fixture 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...
Two cables entering this box, one is coming from the fixture (wire cable
# 1), the other cable coming from switch 2.
* a) using an insulated wire nut connect / join the white
wire coming from fixture + the black
wire of cable coming from switch 2.
* b) connect the black wire coming
from fixture to the common screw of switch 1.
* c) connect the white
wire coming from switch 2 to one of the remaining main screws of switch
1.
* d) connect the red wire coming from switch 2 to the last remaining main
screw of switch 1.
* e) 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 white wire coming
from switch 1 to one of the remaining main screws of switch 2.
* c) connect the red wire coming from switch 1 to the last remaining main screws of switch
2.
* d) please see under important notes in regards to the equipment
grounding conductor (bare wire).
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.
You are allowed to re-designate a white wire to be used as a hot
(ungrounded conductor) in switch circuits but in those cases where a
white wire is used in this manner, you must wrap a piece of black
electrical tape around that white wire inside the box to signify
that is being used as an ungrounded (hot) conductor.
You cannot re-designate a white wire that is actually
connected to the light fixture itself. At the fixture itself, the white
wire must be the grounded conductor (neutral) coming from the 'circuit
power supply cable'.
In the 3 way configuration depicted on this page, the
white wire going from the fixture to switch 1 and the white wire going
from switch 1 to switch 2 have been used to carry a switched ungrounded
conductor (hot) part of the circuit and therefore as stated should have a
piece of black electrical tape wrapped around that wire in the box. The
white wire from the power supply cable that goes to the fixture itself at
the fixture box location is a grounded conductor (neutral) and therefore
is left as white with NO black tape on it.
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 3 wires in it -
black / red / 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 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 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 use wire nuts to join the
bare 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 has 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.
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
(on our sister website 'Wiring Done Right' - will open in new window /
tab) '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....
No onward connections are possible from either of the switch locations
because a grounded conductor (neutral) does not exist with this
configuration at these locations.
From the fixture location...
Onward 'always on circuit power' and 'switched power' is possible from
the fixture location.
Onward Always On Circuit Power... (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 (always on state)
* a) Using an insulated wire nut, attach / join - the
white wire of onward cable + the white wire from the 'circuit power
supply cable' + white wire connected to the grounded conductor (neutral) connection
at fixture.
* b) Using an insulated wire nut, attach / join - the black wire of
onward cable + black wire of 'circuit power supply cable' + white wire
coming from switch 1 (wire cable # 1).
Identification of wires in onward
cable....
Black - Ungrounded conductor (hot)
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 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 from the 'circuit power
supply cable' + white wire connected to the grounded conductor (neutral) connection
at fixture.
* b) Using an insulated wire nut, attach / join the black wire of
onward cable + the black wire coming from switch 1 (wire cable # 1) + black
wire connected to the switched ungrounded conductor (hot) of 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 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 (always
on & switched)
* a) Using an insulated wire nut, attach / join the white
wire of onward cable + the white wire from the 'circuit power supply cable' + the
white wire connected to the grounded conductor (neutral) of fixture.
* b) Using an insulated wire nut, attach / join the red wire of
onward cable + the black wire coming from switch 1 (wire cable # 1) +
the black
wire connected to the switched ungrounded conductor (hot) of fixture.
* c) Using an insulated wire nut, attach / join - the black wire of
onward cable + the black wire of the 'circuit power supply cable' + white wire
coming from switch 1 (wire cable # 1).
Identification of wires in onward
cable....
Black - Ungrounded conductor (hot - always on)
Red - 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.
Written: Nov. 29, 2011
Revised: June 10, 2013 Proof Read / Released: July 7, 2013 Diagrams
redrawn with Transparency: Sept. 2, 2013
By: Donald Kerr
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