Using a volt meter, how can I determine which romex wire is carrying the 110 VAC to a light fixture ?.?

Question

I have 3 romex wires coming out of the fixture, junction off to other rooms. I cannott tell which one is the hot, how can I determine this to wire 3 way switches on to this light ?

Answer 1

best way is to turn on the light at the switch, and then:

1. Find the circuit breaker or fuse that feed this fixture and turn off the power.

2. Undue the wire nut on the hot fire ( black or green) and untwist the wires. Make sure to keep them well separated.

3. Turn the power back on.

4. Use your meter to carefully check for power on each one of the hot wires.

Answer 2

1- Set your meter to AC Scale & 600 VAC, Black lead to common and red to the AC Volts (not Amps).
2- Touch the Black lead of the meter to the metal box or the bare copper wire. With the red lead touch each of the 2 remaining wires in turn.
3- The insulated wire that gives you a reading is the hot wire and it should be black or red in color.
4- 3-way switches usually have a wiring diagram on the box or package it came in.
5- A 3-way switch has three screws. 1 on one side and 2 on the other. (usually the odd screw is a different color).
6- Wiring is easiest to remember is that the two screws on the same side of one switch go directly to the same 2 screws on the other switch AND NO PLACE ELSE !
7- The odd wire brings power into one switch and that single odd screw on the other switch goes to the black wire on the light or lights.
Problems are that the power is already in the fixture box and has to go to the switch, then to the other switch (3-way) the second switch takes the power back to the fixture.
Good Luck if you have to run 2 wires between the switches before getting back to your light and need to install another electrical box and wiring.

Answer 3

If the original was wired by a real electrician. Black will be your hot or line, White will be neutral (same potential as Ground, the green or bare wire) and Red will be what is referred to as the traveler. The traveler goes between both switches.

There should be a diagram that came with the switch that tells you where to hook the traveler and the other two wires.

Shut off the breaker before you start to replace the switch.

Answer 4

If it is (as it usually is) 2 wire romex (means 2 insulated and one uninsulated ground (gnd) wires), the norm is to run from the source (black to black, white to white, gnd to gnd. Note: The black is considered hot and the white as common. In AC, both wires are considered as hot to gnd. Gnd is a wire or anything grounded. The oddity about lights is the switch wire. The norm is to, between the source and the light, the black wire is cut. A romex wire black or white is attached to the source end and the other wire attached to the black wire going to the light, the gnd is attached to the gnd. The added wires are then run to a switch and attached with no specific color scheme. That is the switch run in the black wire and that is all that is needed. For a 3way, with this knowledge follow the directions on the box.
In reference to the voltmeter you should show 110v from the black and the white to any gnd. Its just the standard to use the black as hot and cut it for switches.

Answer 5

One very handy (and safe) item is a "glow stick" voltage tester. It will light up when held next to the hot line and it works right through the insulation (non-contact) It looks like a fat pen and has a pocket clip. They can be purchased at all the big box DIY stores (Home Depot, Lowe's etc) They are great. Mine is a FLUKE brand but GREENLEE makes them and lots of others do too

Answer 6

The hot wire will register 116-121ish when tested against the other two (common and ground). The common and ground together will obviously register 0. The process of elimination will narrow it down to the hot.