12/3 or ?

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  #1  
Old 02-16-07, 04:25 PM
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12/3 or ?

I am in the process of re-wiring an old, rambling house. To run 4 new circuits to the 2nd and 3rd floors I would like to run a single conduit from the load center to a large junction box on the 2nd floor. I am looking at 2 options:

1. Run 2 lengths of 12/3 through the conduit to the junction box (I have an abundance of 12/3 at no cost)

2. Run an approrpiate number of stranded 12 guage wires through the conduit to the junction box

Any thoughts about which option to go for?

The run from the load center to the junction box is about 110 feet.

Service: 100 amp controlled through a newly installed Square D QO load center.

Thanks to whomever...
 
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  #2  
Old 02-16-07, 04:39 PM
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If AFCI protection is required for the bedrooms (it is unless your area does not follow the NEC or does not require it) then you had better decide whether or not you can get 240 volt AFCI breakers, or if 120 volt will have to suffice. If you buy the 120 volt ones then you will have to run individual circuits. If 240 volt ones are your choice then you can run the multi-wire circuits you are suggesting.

Having said that, I would recommend 2 multi-wire circuits. I would use 12 gage wire in conduit to the floors. Then I would split the circuits and use 12-2 to the receptacles and lights.
 
  #3  
Old 02-16-07, 04:40 PM
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It's always better to run individual wires rather than cables through conduit, but it's hard to pass up free stuff.

Why do you need the conduit at all? Can you just run the cables without conduit? Unless there is some particular reason for the conduit, that's usually better.

I assume you're talking about multiwire circuits here. Since the distance is fairly long (110 feet), that's probably a good idea. I suggest you put them on double-pole (not tandem) breakers, even if not required by code.

If you do run cable through conduit, make it a really large conduit.
 
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Old 02-16-07, 05:36 PM
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John coverd it. Why conduit if you have the cable? (suspenders and a belt- but no advantage). Multi-wire.. depends on the end use of the ckts.
If conduit, use junction boxes and thh/wn, and cable from there, more potential this way (providing ckts available).
 
  #5  
Old 02-17-07, 07:06 AM
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Thanks for the feedback and insights. I'll be meditating on the type of wire to run and will report back on how I decided in a few weeks when I get to that part of the job.

Why conduit? I figure extra protection of the wires/cable. The run will be going through a root cellar and up an enclosed raceway on the back wall of the kitchen pantry that has the original (and still functonal) built-in ice box. Once on the second floor the run will go along the top of a knee-wall in an actively used attic storage space.

And yes, I always wear a belt with my suspenders on. When I worked in an old flat-belt run sawmill the old timer on the crew, Hop Herman, recomended wearing both to keep your trousers up, your leather apron in place, and something extra for your workmate to grab on to pull you back if you got to close to the head saw.

Well, I gotta get back to work...again, thanks.
 
  #6  
Old 02-17-07, 07:23 AM
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Here's a suggestion. Use conduit only where you want extra protection, and run your NM through it. If you do this, your conduit does not have to run the entire length. Whereas if you use THHN wires then you must have conduit completely from the start of the THHN to the termination of it.
 
  #7  
Old 02-17-07, 07:55 AM
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Conduit is not all good news. It's a good news/bad news story. The good news is that it provides protection. The bad news is that it traps heat.
 
  #8  
Old 02-18-07, 07:02 AM
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If I were to run 2 lengths of 12/3 cable through conduit, any recommendations for what diameter conduit to use?

Also, help me get this right. One run of 12/3 will give me two circuits, correct? The red and black each become the hot wire in each individual circuit. The white neutral can be wired common to both circuits. The ground wire also becomes common to both circuits.

My intention is to run two lengths of 12/3 from the load center to a large junction box on the second floor from which each line will eminate.

If I go this route my plan is to have each of the 4 circuits protected at the main box, using 20 amp AFCI breakers, as each circuit will be in a bedroom.

Will this keep me to code?
 
  #9  
Old 02-18-07, 09:40 AM
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As mentioned, you can't share a neutral in AFCI-protected circuits, unless you find special 2-pole AFCI breakers. Are these available (or even made) for your panel? I must admit, I always plan so I don't even have to try to find them.

If you are going with a conduit, can you put a box at the other end and use insulated conductors in the conduit and then convert to Romex from that box to the individual bedrooms? You'll still need a neutral for each circuit, but only one ground in the conduit.
 
  #10  
Old 02-18-07, 10:03 AM
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Before installing a multiwire circuit, you must study up on them. There are a number of special rules. Violate any of these rules and you can easily create a very unsafe condition.

Before doing anything, go see if you can find a 20-amp double-pole AFCI breaker for your panel. If not, your whole plan goes down the drain. Even if you do find them, their additionaly cost may more than cancel the savings from the free cable.

If you do run two 12/3 cables, I'd recommend at least 1" conduit.

You might also consider a small subpanel on the top floor.
 
  #11  
Old 02-18-07, 11:57 AM
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Thank you both for your input. As I pull all of the pieces together and reflect upon the info I think I will drop the 12/3, multi-wire option. I can get a 20 amp 2-pole AFCI breaker for my box, but they are expensive. I want to KISS the project while at the same time keeping it within code and without fancy footwork. So it seems I have 2 basic options if I want to protect each circuit from the main house load center --

1. Run four 12/2 romex lines from the load center to the fourth floor, one for each circuit.

or

2. Run an appropriate number of stranded 12 AWG wire via 1" conduit from load center to the second floor junction box, and from there connect with 12/2 romex-wired lines

What would be a minimum diameter conduit to handle 4 12/2 romex lines?

As an alternative to the "direct-line" strategy outlined in the two options above, what might the wiring look like to a small subpanel on the top floor? If I chose to install a 4-6 circuit subpanel on the second floor, what would I need to run from the main house load center to the subpanel?
 
  #12  
Old 02-18-07, 12:27 PM
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Depending on the exact type of conduit you use, the code minimum size for four 12/2 cables would be either 1.5" or 2".

If you run individual conductors, the do not necessarily need to be stranded.

If you put a small subpanel in, the two most common choices would be to install a 30-amp subpanel on 10/3, or a 60-amp subpanel on 6/3. The former supplies up to 7.2KW and the latter up to 14.4KW.
 
  #13  
Old 02-18-07, 06:26 PM
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Excellent info to work with, and I thank you for your continued feedback.

As I've been thinking about this the more inclined I am to tap into a main load center and set-up a sub-panel, probably connecting a 60-amp subpanel on 6/3 as I understand your suggestion. I take it this would be a 6/3 cable coming off of a 60 amp 2-pole breaker in the load center. The subpanel would carry the four 15 amp AFCI breakers.

I have two load centers to choose from. The main house has 100 amp service feeding into a newly installed 125 amp-rated load center. An addition (built 10 years ago) provides a two car garage, workshop, and provides space for my studio and has a separate service entry and load center with 100 amp service coming into a 125 amp-rated load center. Both are separately metered, and both have main 100 amp main service breakers at the meters.

The main house load center would require about 110 feet of run from the load center to a sub-panel. The addition load center would require about 60 feet. Aside from the cost, is there any "code" reason why 4 circuits in the main house could not be fed off of a sub-panel supplied by the "garage line" rather than the "house line"?
 
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