How do you get uninterrupted power out of a three way light switch to power another light when the power is coming into the light box?

Answer 1

to wire a 3-way like this you first need to run 14/3 romex wire from the light box to each of the 2 switch locations. at each switch connect wires as follows: white wire to common screw(usually black or brass) connect red and black wire to silver colored screws, does not matter which way. in the light box you need to identify you incoming power, once you have identified that wire connect one of the white wires from the new 14/3 romex to it,secure with wire nut.the red and black in each 14/3 romex are connected red to red, black to black. this should leave you with one white wire frm a 14/3 romex, this connects to the black wire of your light fixture, the white of your light fixture connects to the white of the incoming power wire.

Answer 2

If the two three-way switches are wired correctly, only one is likely to have an uninterrupted Hot wire (Black). Sometimes a switch box may have other circuits, but you may be out of luck. Get a voltmeter and check voltage on all possible connections with the four possible switch positions. Both Up, switch A Up and Switch B Down. Switch A Down and Switch B Up. Both switches up.

Answer 3

Answer for USA, Canada and countries running a 60 Hz supply service.

You have to run a 12/3 with ground, assuming you are using cable, to the other 3-way switch. 2 conductors are your travelers from one switch to the other and the 3rd conductor is the switch leg that ties to the wire going to the fixture.

This is the sequence: The hot from the panel connects to the common terminal, often a black screw, of the first 3-way switch. 2 travelers connect to the other terminals, often brass in color, and run to the similar terminals on the other switch. From the common terminal of that switch a conductor runs back to the other box and connects to the black or colored conductor going to the fixture. The neutral conductor from the fixture, which should be white, connects to the neutral going back to the panel.

In this installation you are using the white of the 12/3 as a hot wire. That's ok. It is common practice to mark this conductor with black tape, but I know of no code requirement to do so.

As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.

Before you do any work yourself,

on electrical circuits, equipment or appliances

always use a test meter to ensure the circuit is, in fact, de-energized.

IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB

SAFELY AND COMPETENTLY

REFER THIS WORK TO QUALIFIED PROFESSIONALS.