I'd like to add some lights on an existing switched lighting circuit/wire. First, can I simply splice into the wire in a new box and add a couple of lights? Second, how can I determine which wire is the one with the switched light? There are several accessible wires in my attic but I don't know which one the light is powered from. All of the wires are on the same power circuit from the panel box.

7/9/2014 10:05:46 PM

get http://www.lowes.com/pd_464310-295-10035K_4294618094__?productId=50125855&Ns=p_product_qty_sales_dollar|1&pl=1¤tURL=%3FNs%3Dp_product_qty_sales_dollar%7C1&facetInfo= and http://www.lowes.com/pd_327266-2137-CH11487_0__?productId=3355612&Ntt=wiring+book&pl=1¤tURL=%3FNtt%3Dwiring%2Bbook&facetInfo= take it from there. once you know the basics something like this will be easy.

7/9/2014 10:48:24 PM

are you wanting to add lights downstream of an existing switch, or add a new switch to control the new lights?

7/10/2014 8:48:09 AM

^this. If you just want to add lights to an existing switch/circuit, then you can run the wire from one of the existing fixtures to the new fixtures and everything will turn on/off at the same time from the same switch. I'm sure you already know this but make sure the power is off and that you aren't overloading the circuit. 15A115v won't kill you but it will scare the bejezzus out of you if it gets you and falling off the ladder might. I also recommend the Complete Wiring book suggested by stowaway and at least this: http://www.lowes.com/pd_464286-295-40110N_0__?productId=50129720&Ntt=electrical+tester&pl=1¤tURL=%3FNtt%3Delectrical%2Btester&facetInfo= just to be certain the circuit isn't live before you start messing with it. Panel boxes aren't always labeled correctly. I'm guessing that you have a 15A feed into your attic for lights and any receptacles so keep in mind that the more light wattage you add to the circuit, the less you will have available for any receptacles.

7/10/2014 9:06:29 AM

thanks for the responses.

I do want the new lights to operate off of the existing switch, hence identifying which wire goes from the switch to the existing light. My only issue with coming straight off the existing light is that it's on the ceiling of my garage and above it is my bonus room (and on either side of the bonus room is accessible attic, where the existing wires are located), so not very accessible. I want to add the new lights elsewhere in the garage, so I either have to run wire on the outside of the drywall (not a deal breaker, but not ideal), or find the wire in the attic and splice into there and run new wire in that space to the new light locations.

Yes, it is a 15A circuit, though I do need to figure out what all is on the garage circuit and bonus room circuit (I would not be surprised if the electrician mixed circuits between these, or even another circuit, as the switch for the garage light is in my laundry room with 3 other switches for various lights).

[Edited on July 10, 2014 at 10:17 AM. Reason : .]

7/10/2014 10:13:51 AM

Depending on where you want to add the new light and if the ceiling joists in your garage run the right way, you might be able to feed the wire from an existing light fixture to the new light and stay in the same joist cavity. What kind of lights do you want to add? Fluorescent or something else? I ask because unless you are adding fluorescent lights, you will need to add a box in the ceiling for the new fixture so you will have to make a hole in the ceiling anyway...you can make the hole and see if there is any wire for the lights accessible from the hole.

Another suggestion is to turn on the garage lights and use the tool I suggested to check if all of the wires in your attic are are hot (it will sense current through the wire insulation). Then turn off the garage lights using the switch (not the breaker) and check to see if any of the attic wires are no longer hot. If so, this will let you know that the "non-hot" wire runs from the switch to a garage light fixture. Of course, I would do this a couple of times before actually cutting into the wire just to be sure.

7/10/2014 11:21:31 AM

I do believe the joists run in the direction of at least one light I want to put in. And at that point on the ceiling, the attic is overhead, so I can come above and cross over the joists to reach the other lights... one issue is that there is insulation in the ceiling where the existing light is located.

It would 3 florescent lights... maybe 4.

[Edited on July 10, 2014 at 11:44 AM. Reason : .]

7/10/2014 11:44:17 AM