Stumped by 3-way Switch Scenario

DIY-Wannabe · 01-06-2011, 12:44 AM

My 1st ever DIY post so, hopefully all the needed details are included... Have done a fair bit of wiring without any difficulty but am stumped here... Objective is to have 2 light switches control a basement light - one switch located upstairs and the other in basement.

I have free reign to wire the light and basement switch however necessary, but cannot run any new wire to the upstairs switch (already exists) without doing damage and I don't want to go that route (pretty sure I won't have to)...

Scenario:
There's a basement light that was solely powered from an upstairs switch. I'd like to continue using that switch upstairs (make it a 3-way) and add a 2nd 3-way switch in basement to control the light.

I have 14/2 wire from electrical panel going into a junction box. At that junction box, I have a 14/3 wire going to the upstairs switch noted above (the switch is in a triple gang box, and from there, the power is distributed to a number of other fixtures/receptacles in house). This is the part throwing me off because I essentially need to deliver the power to that gang box through the 14/3 wire, but also bring it back through same 14/3 wire from the upstairs switch and continue the 3-way circuit.

My preference would be to run whatever wire necessary from junction box to basement switch and from basement switch to the light. Beggar's can't be choosers though! I would really appreciate an outline or link to a diagram that explains how to achieve this?!?

kbsparky · 01-06-2011, 01:08 AM

Not possible without re-feeding the other items in the circuit. If you can back-feed one of the other lights or receptacles from that junction box in the basement, then you could isolate the 14/3 cable and reassign the conductors for use with your 3-way switch arrangement.

Stubbie · 01-06-2011, 01:11 AM

Forget the junction box for the 3 way. Run power to the basement 3 way on 14/2 G, then run a 14/3 G from downstairs switchbox to the upstairs 3 way switch. Then run a 14/2 g from the downstairs 3 way switch box to the light. If you want to keep the jb then splice 14/3 G to existing 14/3 G to get the 14/3 to the downstairs switchbox. Also splice 14/2 g to the incoming power at the junction box and extend it to the downstairs switch box to get constant power to that switchbox. I can give you a diagram if that will help. Do you want the junction box or no?

Stubbie · 01-06-2011, 01:24 AM

Just rereading I see the 14/3 is getting power to the upstairs switchbox so you cannot use it as KBsparky said You will have to get a new cable to the upstairs switchbox.

DIY-Wannabe · 01-06-2011, 08:10 AM

Alrighty then!! Feels a bit better knowing I couldn't figure out the impossible and am sure glad I asked before attempting anything... Thanks for your help guys - will brainstorm some ideas to get power to that upstairs circuit and hopefully free up the 14/3 G cable to the switch. (at least I've learned how to properly identify the cable!)

Stubbie · 01-06-2011, 11:48 AM

It's a little unusual to have 14/2 in a junction box then 14/3 to a switch box if those are the only two cables in the junction box and the junction box isn't actually a fixture box that is being switched from the upstairs switch box. There is no reason to have two hots (black and red) in the 14/3 each carrying power to the triple gang box upstairs. Only one hot is needed for that purpose.

joed · 01-06-2011, 12:26 PM

Quote:

Originally Posted by Stubbie

It's a little unusual to have 14/2 in a junction box then 14/3 to a switch box if those are the only two cables in the junction box and the junction box isn't actually a fixture box that is being switched from the upstairs switch box. There is no reason to have two hots (black and red) in the 14/3 each carrying power to the triple gang box upstairs. Only one hot is needed for that purpose.

There is a very good reason. The power comes in at the light below and unswitched power goes out of the switch box above. You need a neutral wire, a hot wire and a switched hot returning to the fixture.

DIY-Wannabe · 01-06-2011, 03:57 PM

Correct! 14/2 G black from hydro panel met with 14/3 G black to upstairs switch. Red from the 14/3 G met the black to light.

Stubbie · 01-06-2011, 05:05 PM

Quote:

Originally Posted by joed

There is a very good reason. The power comes in at the light below and unswitched power goes out of the switch box above. You need a neutral wire, a hot wire and a switched hot returning to the fixture.

Joe ... that is exactly what I said....

When someone says junction box I don't immediately consider the jb being a light fixture box. What I was saying is unless the 14/3 is being used to switch a light at the jb then two constant hots is not necessary to the upstairs switch box.

This is what I was saying would make sense in his description but I wasn't sure that was what he had.

kbsparky · 01-06-2011, 07:34 PM

Quote:

Originally Posted by Stubbie

Just rereading I see the 14/3 is getting power to the upstairs switchbox so you cannot use it as KBsparky said You will have to get a new cable to the upstairs switchbox.

No so fast, Stubbie. The OP stated it was not feasible to feed another wire to that switchbox. OK, I accept that.

What you missed was I suggested that the rest of the circuit might be back-fed from anywhere else -- an outlet, light, or switch -- doesn't matter where, as long as its the same circuit. If the basement is open and unfinished, then that might be an easier task than trying to get another line up to that 3-gang box upstairs.

IF one can back-feed the rest of the circuit, then the existing 3-wire cable is no longer needed to act as the feed for it, thus allowing one to reassign those conductors as travelers in a properly wired 3-way switching scenario.

Stubbie · 01-06-2011, 07:55 PM

Quote:

Originally Posted by kbsparky

No so fast, Stubbie. The OP stated it was not feasible to feed another wire to that switchbox. OK, I accept that.

What you missed was I suggested that the rest of the circuit might be back-fed from anywhere else -- an outlet, light, or switch -- doesn't matter where, as long as its the same circuit. If the basement is open and unfinished, then that might be an easier task than trying to get another line up to that 3-gang box upstairs.

IF one can back-feed the rest of the circuit, then the existing 3-wire cable is no longer needed to act as the feed for it, thus allowing one to reassign those conductors as travelers in a properly wired 3-way switching scenario.

Yes I would have to agree with that and I did overlook that possibility thinking it would be just as hard to backfeed as it would to get a new cable to the switch box. Your absolutely correct if he could free up the 14/3 he would be in business.