Use ONE 12/3 cable between one fixture and two switches?

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  #1  
Old 06-27-06, 09:34 AM
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Use ONE 12/3 cable between one fixture and two switches?

Hi - sorry if that subject line sounds a bit dense! My objective is as follows:

I have a fixture which is a combination ceiling fan and lights. I would like to control those lights from two locations (3-way) and also have those same lights be on a dimmer. The fan will only be controlled from a single location, single pole switch.

Here's what I've done (and want to see if this is OK!):

3-way toggle switch #1: 12/2 is power source and 12/3 travels to switch #2 [below].
12/2 WHT wire connects with 12/3 WHT wire.
12/2 BLK wire goes to common terminal.
12/3 RED and 12/3 BLK are connected to traveler terminals.

3-way dimmer switch #2: Two 12/3 cables meet here (A & B). 12/3A travels from switch #1 [above]. 12/3B goes out to the fixture.
12/3A RED and BLK are connected to traveler terminals.
12/3A WHT wire connects with all other WHT wires.
12/3B RED wire goes to the lights on the ceiling fan fixture.
12/3B BLK wire see below in switch #3.

Single-pole fan switch #3: New 12/2 power source enters here and its BLK wire feeds one of the terminals on this switch. The other terminal (for outgoing) uses the BLK wire from 12/3B (mentioned above in switch #2) to bring power to the fan motor on the ceiling fan fixture. All WHT wires are coupled together.

Final note -- the two 12/2 power sources mentioned earlier are both part of the same circuit. Junction boxes were introduced to send power to different physical locations, but all are sourced from the same single 20A circuit.

Hope this isn't too difficult to read/decipher. Thanks for any time spent/comments offered.

-DaveC
 
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  #2  
Old 06-27-06, 09:56 AM
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Wrong.

Remove the second power cable, the one entering the second switch box.

Replace the 12-3 between the switch boxes with 12-2-2 or 12-4. Use the extra wire to carry an unswitched hot between the fixtures, which you connect to the input side of the fan switch.

While what you have sounds like it would work, it would create a current imbalance because of the dual neutral wires. This is wrong and against code, and if metal boxes are involved it is dangerous..
 

Last edited by racraft; 06-27-06 at 10:06 AM.
  #3  
Old 06-27-06, 10:00 AM
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That is EXACTLY what I was looking for. Thank you so much for the quick and informative reply.

(I thought it might be too good to be true!)
 
  #4  
Old 06-27-06, 10:08 AM
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I just realized there is an easier way to fix this, where you don't need 12-2-2 or 12-4.

Remove the power feed to the first switch.

Use the 12-3 between the switches as a switch loop between the the two three way switches.
 

Last edited by racraft; 06-27-06 at 10:57 AM.
  #5  
Old 06-27-06, 10:12 AM
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Oops...two more questions

Sorry...

1 - Would Bob's solution also require replacing 3-way toggle switch #1 with another type of switch? If so, would that be a 4-way?

2 - Would an OK alternate solution be to remove the 12/3B cable completely, replace it with 12/2 for the lights and introduce another 12/2 that delivers power to the fan motor? This would effectively put those dual neutrals back on their own wires.
 
  #6  
Old 06-27-06, 10:15 AM
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1. No.

2. Maybe. The neutrals for the fan and the light would have to be separate. Sometimes they are, sometimes they are not.

The best solution is my post just prior to this one.
 
  #7  
Old 06-27-06, 10:41 AM
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Thank you again for your time Bob. Very good point about the neutral on the fixture. It is indeed only one!

So now I just want to ensure I understand you're most recent solution correctly (the solution without the 12/4).

1) Completely remove 12/2 power source from 3-way toggle switch #1. That leaves the common terminal free for now...

2) Here's where I'm having trouble following:

"Use the 12-3 between the fiixtures as a switch loop between the the two three way fixtures."

There's only one fixture in this instance (ceiling/light combo which has 3 wires: BLK, BLU, WHT).

I'm probably asking for this to be spelled out for me, but I completely understand if that is beyond what you are willing to offer me at this time.

-DaveC
 
  #8  
Old 06-27-06, 11:03 AM
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Sorry, that should have been "between the switches", and I have corrected it.

At the first three way switch where you remove the power wire, connect the white wire to the common. Re-identify the white wire as hot with a black marker. Connect the red and black to the travelers.

At the three way switch and the two way switch connect as follows:

Using a wire nut and a pigtail, connect the power black wire to the three way white wire (re-identify with black marker as hot) that goes to the other switch and to the input of the two way switch.

Connect the power white wire to the white wire that goes to the fixture.

Connect the red and black three way wires from the other switch to the travelers of the three way dimmer.

Connect the black wire for the fixture to the common of the three way dimmer.

Connect the red wire for the fixture to the output of the two way switch.

At the fixture connect the red wire to the fan hot, the black wire to the light hot, and the white wire to fixture neutral.

Connect all ground wires at every location.
 

Last edited by racraft; 06-27-06 at 11:39 AM.
  #9  
Old 06-27-06, 11:30 AM
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Brilliant! You turned the circuit around and used the 12-3 white wire to bring power over to switch #1, which becomes the "end".

I failed to see it from this angle. Should have realized that since switch #2 and #3 are in the same box together, it would be easier to source the circuit from that side.

I'm guessing that electricians "see" this kind of thing all the time, so not such a big deal, but to a novice like myself it's kind of cool.

I'll post a follow up in a day or so with results.

Many thanks Bob!
 
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