3 way switch

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Old 12-28-05, 02:33 PM
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3 way switch

im going to be installing a light going down my basement stairs...i want to have a 3 way switch on top and bottom of stairs...what is the best way to run it,should i bring the power to the switch and then to the ceiling light...i have been reading up on the set up in wiring simplified and hd wiring 123 book....i understand i need to run 12/2 to one switch ,then 12/3 to the second switch,and then 12/2 back to the light itself....

now im going to just rough everything in,then i will be asking for help with the final wiring of the switches,cause what i am understanding is the 12/3 white<neutral> with have to be marked black cause it will become a hot...

this will be tapped into my attic fan (3.2amps) 20 amp line,i will get power from junction box ,12/2 to switch,12/3 to second switch,and 12/2 back to ceiling light...unless yous guys suggest running power to ceiling light then run to the switches...and im in new york and use ac cable(bx)...thanks once again for all the help and safe advice yous give me....
 
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Old 12-28-05, 02:52 PM
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Electrically it does not matter where you bring power into the circuit. You can bring power into the light, or power into either switch. Further, you can run the wires in whatever way makes sense. All that is important is that you have enough conductors.

It is easier for most people to understand if they run power to one of the switches, then to the second switch, then to the light, but do whatever makes sense for your layout. It might help to draw a picture first.
 
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Old 12-28-05, 08:15 PM
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3 way switch

Just remember on a three way switch, there is one screw that is standing alone at the "bottom", and it is usually andonized (black), but not always. If you pick up a three way switch by pinching it with your fingers on screws, the remaining screw is the one I am talking about. This screw becomes "line" on one switch and "load" on the other one. Your remaining two wires, red and white, become runners and it doesn't matter how you hook them up to the switch. One goes on one of the two "top" screws, and the other one on the last screw. Same with the other switch. Hook your power up to one of the andonized screws on one switch and the light to the other switch andonized screw. All your neutrals are tied together.
Unlike a regular single pole single throw switch which only "makes" or "breaks" a connection, the three way switch toggles between the red and white wires, making one hot when switched in one position and "not" in the other.

Did I muddy up the water too much. good luck with your hook up.

Larry
 
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Old 12-28-05, 11:08 PM
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Chandler explained it well, but I would like to add two thumb rules:
-you should always have three conductors between the switches.
(The power, using two conductors, can run to either switch box or to the load being switched. Finally, you will need another two conductor cable to go from one of the switches to the load.)
-The "common" screw of one switch must be connected to the "line" or power to the circuit. The "common" screw of the other switch must be connected to the "load".
With these two rules, you should be able to figure out how the wires run. Read chandler's last post for wiring, except I believe it is more common to use red and black as the travelers, especially since we often use the white as a neutral. Sometimes the neutral is used as a "switch leg" (to carry the line or load to the other box) and is marked with black or red electrical tape at each end.
 
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Old 12-29-05, 05:50 PM
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3 way switch

I usually use the white and red as runners because it will leave a black wire going to the load and reduce confusion at the applicance in case the hot lead was not taped (when using white as load).

Larry
 
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