I’m trying to add a 3 way switch to my basement stairs on a basement remodel and trying to confirm what size box I would need for the connections.
In a junction box currently I have which I believe is 14/2 power in and 14/2 to the existing top of the stairs switch. And then I have 12/2 going to the first recessed light in succession. I want to change the first switch and add an existing for 3 way.
I was planning on pulling the old switch and wire out and running 12/3 to it and then 12/3 to the new switch.
So if I’m understanding correctly…
14/2 – 4 in
12/2 – 4.5 in
2- 12/3 – 14 in
Ground – 2.25
24.75 in box minimum.
I used 12/2 to the light because that’s what I had lying around. The breaker that is attached to this circuit is 15 amps also has other lights and outlets throughout the house, but could I potentially use 14/3 for the new switches instead of 12/3?
Unless the original feed is 12/2 then I guess it would be 25.25 cubic in.
was planning on just getting a bigger metal box than I currently have attached to the joist.
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14/3 would be fine.
You can also run the line to the new switch from the first switch box, if that works, instead of running both runs to your junction box.
In fact the only new wire you would need to run is 14/3 from the first switch box to the second switch box. (if there is room in the first switch box.)
Everything is pretty much open and accessible at this point except the initial light switch at the top of the steps.
However the new switch I want to install is almost directly below about 8-10ft below. So how would I wire it up if I just ran 14/3 from from switch A at the top of the stairs to new to install switch B.
Would save me some wire as oppose to having both A and B ran to the junction box where then light and power feed come in.
If the current wire has a single run of 14/2 to the switch, (and it works)
that box will have a black and white wire each hooked to the switch.
In this case the black has feed of power to the switch, and white takes the switched power back for distribution.
Remove this switch and run new 14/3 between the boxes.
In the old box, hook the 14/2 black to the different color screw on the first three way switch. hook the white wire from the 14/2 to the white in the 14/3, and hook the red and black from the 14/3 to the same color screws on the first switch. These will be travelers to the second switch.
In the second (new) switch box hook the black and red from the 14/3 to the same color screws, and hook the white wire to the different color screw on the switch.
power will go from your distribution box to the first switch, down one of the travelers, and if both switches are set to the same traveler wire, then pass from the second switch back to the junction in the first box, and back to your junction box where it feeds the lighting circuit. (if the switches do not match positions, the light is off.)
Keep in mind all these wires will be hot at some point, and the white wires should at a minimum be wrapped with some black tape or marked to remind you and future observers that it is not neutral.
Also, keep in mind that this is not really up to current code, which now wants you to only use white wires as neutral, and run extra wires around. You need to run the neutral anyway if the switch will need some power and neutral to operate, like one with a light, or a smart switch you can command from the internet.
I mainly used the 12/2 wire to the lights because I wasn’t 100% certain the original wiring was 14/2 and didn’t want to use something less. I know it’s a 15 amp circuit but is there an easy way to tell the gauge. House was built in 68’ and the wiring has a shiny silver almost cloth feel to the outer jacket. But i don’t see any markings on iT
You can measure the conductor, or compare a small length of wire you know (like the end of one of the wires inside the12/2 you have.)
They sell wire gauge checkers, but a micrometer or caliper would do as well for your purposes.
12 gauge is 2.053 mm or 0.0971 in diameter (a little over 3/32 in)
14 gauge is 1.628 mm or 0.0633 in diameter (a little over 1/16 in)
So upon further review it appears that the existing wire is indeed 12 gauge. It matches up too a piece of new 12/2 Romex I had.
Also the white wire coming to the existing switch at the top of the stairs appears to be hot and wasn’t marked. (Switched loop?) I’m guessing??
I also noticed a little charring on the casing of the wire heading to that switch. It was pulled around a hot water pipe that runs to my baseboard heat.
Should I just replace that hole section of 12/2 from the switch to the junction with the power feed and lights connection with the 12/3? If that makes sense. Which in turn I would def need a bigger junction box and run the new switch wire from that location to.
If the circuit has a 15 amp breaker, and you have some reasonable loads on the lights, you can still use 14 Ga wire.
really is up to you.
if there are only the two wires to that old switch, they both should be hot when the circuit is on, and only one hot when the circuit is off.
Neither one would be neutral.
hopefully you are turning off the breaker when undoing the wires...
Excellent, great explanation and thank you for saving me some wire haha!!
Or you could just change the existing switch to a Lutron Casetas switch and use the Lutron Pico remote switch which you can mount anywhere you want with no wiring issues
Just install a deep 4 square metal box with a single gang plaster ring. That will give you lots of room.