Lighting, Light Fixtures, Ceiling and Exhaust Fans - Lighting Wiring Problem

I am installing some lighting to my attic (with a three way switch) before sheetrocking, and I notice that the cable coming in to the room is 3-wire cable (black, white, red and ground).

To wire up the lighting with a 2-wire I would have done the following (hopefully its correct), but don't know what to do with 3-wire or if there's another way than this:

1) connect black to common from feed to the 1st switch, then connect a 3-wire cable going to the light fixture, with whites on a wire nut (black and red to the switch one)
2) at the light, with another 3-wire going to the next switch, I would connect the red wires on a nut, white from the first switch to the white on the fixture, black from the first switch to the white going to the second switch and recode, then the black from the fixture going to the black on the second switch, and grounds under one nut
3) at the second switch connect the black to the common and the red and recoded white to the switch

Thanks for your help

Your description of what you would have done with one less wire is correct.

However, there are many reasons why you might currently have an extra wire in some random cable "coming in to the room". You gave us nothing to go on. The first thing is to determine where this cable "coming in to the room" comes from, and how it is connected there. Is that possible? If not, give us any clues you have, such as where this cable runs, where it ends, if it was ever connected to anything, who might have put it in, etc.

Sorry, didn't explain it very well.

The feed is via conduit running up the side of the house from the basement (where the breaker box is). Firstly it goes into the level below where it feeds a receptacle the previous owner used for an AC unit (nothing else being fed). Then it comes via the conduit into the attic and has 2 receptacles being powered.

Would the way I explained be the best considering Im installing low voltage recessed lighting - if that matters.

Hope this helps.

It sounds like you might have a multiwire circuit coming up into the attic. That is trwo circuits sharing one neutral wire. It should take two breakers or one double breaker to turn of power to the black and red.

Your wire connections are OK for this circuit.

Yes its connected to two breakers. Is this unusual? Will it affect my lighting wiring?

Is it connected to two breakers, or to one double-pole breaker? Is the breaker(s) a 15-amp or 20-amp breaker? If not, how many amps is it? How is it connected to the breaker(s)? Are the black and red connected to the breaker(s) and the white connected to the neutral bar? How exactly is it connected to the A/C receptacle and to the two receptacles in the attic?

If you answer all of the above questions, then we'll know exactly what's going on. Otherwise, we're just guessing.

The connection at the breaker box is red to one 20A breaker and the black to another 20A breaker.

At the AC recep. there is a red, white and ground.

The connections coming in to the attic are as follows:
1) 2 reds coming in, one from the main feed and then another connection going via conduit outside to another part of the room which is currently not used for anything (connections just under wire nuts but I may put a recep. there). Connected to the 2 reds is a black from 2-wire cable (black white and ground) going to the 2 recep. box

2) 4 whites all under a nut

3) 3 blacks, which comprises of 2 from outside and 1 going to some temporary lighting that the previous guy put up to do his work with (this will be removed but I could probably just use this for my lighting wiring??)

4) 4 ground wires

Thanks for your help

If you have a voltmeter, measure the voltage between the red and black wires at the panel. If you get 240 volts, then you are in good shape. If you get 0 volts, then you have trouble. Let us know.

Assuming that you get 240 volts in the above test, then you have a standard multiwire circuit. In you attic, you may use either the red and white, or the black and white. Just ignore the wire you decide not to use.

If you decide to put any GFCI receptacles in the attic, special precautions are needed due to the multiwire circuit. You cannot connect a shared neutral to the "load" side of the receptacle. So you can either just use the "line" side and leave the "load" side unused, or else you can make sure that the neutral is split off before going to the GFCI.

Try to find some sources of information on multiwire circuits to read up on them. They are safe, but only if properly understood and used. The $6 green paperback Wiring Simplified covers it nicely.

Ok thanks for replying, I'll do some research on it, and I'll also get a voltmeter over the next couple of days.

As I understand from whats going on, the red is getting power from one breaker and the black the other, but as it stands the red is connected to the receptacle and the "work lights" on the black - so should I just disconnect the work lights and take power for the new lights from the receptacle instead (assuming the voltmeter checks out)?

If the multiwire is propely wired (each hot should come from opposite legs of the utility supply), you can use either circuit for any load. It would be best to try to balance the loads, so each circuit draws as close to the same amount of power as possible.

If you measure 240 volts red to black you do not need to change anything.
If you do not measure 240 volts red to black you need to move one of the breakers in the panel to get 240 volts red to black.

Ok I see. I thought that wherever the breaker is in the panel it would give an even load. The two breakers are on the same side, so by opposite legs do you mean this would be ok or that it needs to be on the other side?

If the two breakers are on the same side of the panel, and are full-size breakers, and are directly next to each other (e.g., slots 16 and 18), then that would be correct for most panels. The voltage check is the definitive check.

Following on from this post last week, I purchased a voltmeter that has 120 and 240v lights. It appears it can be used to plug into a receptacle or bare wire red to black.

Would red to black be the best way to check this?
Thanks

Not only the best way, the only way.