First we will identify the wire colors that might be encountered in 120v/240v single phase AC residential power systems. A phase is always signified by the color black and is known as a HOT wire 120v and the B phase is the red wire also a HOT wire 120v but 180 degrees out of phase with the black wire which means that these two phases A and B are opposite of each other. As the voltage (v) of the black wire increases toward maximum voltage the red wire decreases toward a maximum negative voltage with respect to the neutral (White wire) also known as the grounded conductor and not confused with the green grounding conductor (Tied directly to an 8′ ft ground rod driven into the earth.)
There are basically three ways that a fixture can be wired:
1.) The first way is if the light was wired by bringing the power to the switch first and then running a wire up to the light. wire to the switch is 14-2 w/G romex that will have black white and green or bare copper wires in a heavily insulated jacket. The same type of wire is used to run from the switch to the light fixture. Therefore whites tie together and the greens tie together and to the green screw in the switch box the blacks tie to the top and bottom of the switch. ONE of the blacks is your power wire feeding the switch HOT and the other black wire that runs to your light is called the switch leg. When the switch is turned on the power feeds thru the switch to the switch leg and to the light box. Now with this wiring configuration hook up of your light is simply following the colors black to black white to white and green to green and the green screw in the box.
2.) A 14-3 w/G is sometimes used if the electrician wants to bring the black HOT wire up through the light box and feed other fixtures or power outlets in different rooms. The 14-3 w/G will contain colored wires black red white and green or bare. When using this wire from the light box to the fixture the hook up remains basically the same except that you would use the red wire to go up to the light as a switch leg and the black wire will tie to the black in the switch and go up to the light fixture at which point another romex cable can be added to the fixture box so that it may provide power for another room. In the fixture box all colors still tie together except the red wire from the switch ties to the black wire of the fixture the black from the switch ties to the black that’s continuing on to another room the whites tie together with the white from the fixture and all greens tie together. Use a clock wise twist when mating wires together and then apply a yellow or red wire nut tightly to ensure a good tight connection then roll the wire up into the box.
3.) The third way a light can be wired is by feeding the power wire directly to the fixture box. Now you have to drop a switch leg and power wire down to the switch so that the switch can control the light fixture. Using 14-2 w/G from the fixture box to the switch box we will use black tape to mark the white wire in the fixture box to a length of at lest 8" inches and we will do the same thing at the switch box. Now tie the marked white wire to one side of the switch and hook the black wire to the other side of the switch tie the greens together and to the box. At the fixture box we will use the marked white wire to power out switch so we will connect it to the incoming black HOT wire the black wire from our switch is our switch leg that will feed power to the light when the switch is turned on. connect the black wire from the switch to the fixtures black wire connect the white wire coming in with the power to the white on the fixture as well as any other white wires that may be leaving the fixtures box to supply power to other rooms.
If your light is capable of being turned on and off from two or more switch locations such as seen in large living rooms then that means that the switches that are controlling the light are 3 way or 4 way switching control circuits. If this is the case the best thing you can do is call an Electrician because most novices end up connecting the wrong wires together and never get it to work correctly. By leaving the wiring alone a qualified Electrician can fix it in no time. But when people mess with the wires then we have to use a meter to find the HOT wires and the travelers to make it work again.
Also while the Electrician is there have them balance your panel it will pay for the service call by saving wasted power that returns on the neutral straight in to the ground. I had 5amps on my neutral because two computers were connected to the same phase and after I balanced my panel I dropped the neutral current to less than 1/2 amp. Thanks for your time and REMEMBER SMILE IT ADDS TO YOUR FACE VALUE !
