Space, Safety and Money vs. Wire


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Old 04-30-11, 07:55 PM
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Space, Safety and Money vs. Wire

I'm adding 6 new circuits to my system, and I have a question about what type of wire to use.

To get from the panel to the area of the house where I need the new circuits, I have only a small chase to bring up the cables. The chase is probably 3" by 2", and about 12' long.

I believe I have enough room to bring through six 12-2 cables, but I feel like it would get crowded, take more time, and in general just add a lot of cables to an already crowded area of the house. A subpanel is not an option (nowhere to put it).

My questions:

Is there a restriction as to how many 12-2 cables can occupy a given area (not in a conduit)?

Would I be better off using 12-3, to go from 6 cables to 3?

Would I be better off using 12-4, as opposed to 12-3?

What makes the most sense to you guys?

Thanks.
 
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Old 04-30-11, 08:24 PM
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Originally Posted by PenCup
Is there a restriction as to how many 12-2 cables can occupy a given area (not in a conduit)?
Yes, there is restrictions. On cables bundled for more than 24" you have to start derating them. Derating starts at the 90 degree listing for THHN since NM-b has THHN wires in them.

Originally Posted by PenCup
Would I be better off using 12-3, to go from 6 cables to 3?
Yes, You would have to use 2 pole breakers but it is a small price to pay for pulling in half the cables. Also your wires would then be 9 in the bundle. Derating factor is 70% at 9 wires. THHN is rated at 30 amps under the 90 degree column 30 x .70 = 21 amps so you are still fine at 20 amps.

Originally Posted by PenCup
Would I be better off using 12-4, as opposed to 12-3?
With the extra cost of 12/4 you would likely not gain anything compared with using two pole breakers. Plus you would now have 12 current carrying wires which means you would be at 50% derating factor. 30 x .50 = 15 amps
 
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Old 04-30-11, 08:29 PM
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Thanks Toblyn.

Let me just add this twist, since you brought up two pole breakers:

The new circuits would need to tie into tandem breakers. So if I went with 12-3, I would be able to pull fewer cables, but would need to be mindful to keep the both "hots" from each 12-3 on a separate phase inside the panel?
 
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Old 04-30-11, 08:39 PM
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Yes, both hots will need to land on separate phases, otherwise you risk overloading the neutral. I should have mentioned the two pole breaker rule went to effect as of 2008 code. If your not on 2008 code single pole breakers are fine. If you are on 2008 code you will be required to get two pole tandems which ups the cost a bit depending on your type panel. I should also mention if this is for a bedroom AFCI breakers come into play as of 2005 code and other general areas (except bathrooms or kitchens) as of 2008 code.

Are you sure there is no place to install a sub panel? Many cases they can be quite camouflaged with a cabinet door or placed behind a person door.
 
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Old 04-30-11, 09:19 PM
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I've been poking around since I made my initial post. A subpanel might actually work, I'd just have to extend the cables a few feet farther. A little more information, than a couple of questions:

My house is a duplex. In my basement I have a main panel that only feeds two other panels (call them A and B). Panel B is the panel that I had intended to take the 6 new circuits out of.

There are 8 breaker spaces in Panel B. Two are occupied by the main shut off, two are occupied by a 30amp range, two are in use by existing circuits, and two are empty. If I were to install a subpanel after panel B to handle the 6 new circuits, what size cable would I use?
 
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Old 04-30-11, 10:36 PM
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If I were to install a subpanel after panel B to handle the 6 new circuits, what size cable would I use?
Depends on the expected loads. If no electric heater, dryers, or stoves probably a 60a would be more then enough. That would be #6.
 
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Old 05-01-11, 06:05 AM
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If I were to install a subpanel after panel B to handle the 6 new circuits, what size cable would I use?
What size is the breaker feeding the sub? You cant just pull 60A off a panel fed by 40A
 
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Old 05-01-11, 06:32 AM
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You could change out the small panel for a larger one.

IIRC Cutler-Hammer is the only one making two-pole AFCIs.
 
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Old 05-01-11, 09:14 AM
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40A is all I need. So #8 wire.

What are the major things to consider when finding a location for a subpanel?
 
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Old 05-01-11, 09:32 AM
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You need a space 30" wide by 36" deep. The panel does not need to be centered in the 30" width. Imagine a refrigerator size box in front of the panel. You also need lighting. The panel door needs to be able to open at least 90 degrees. You should not have piping or ductwork in the panel workspace.
 
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Old 05-01-11, 09:42 AM
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You also may not have a panel in a bathroom or a clothes closet. You may have a panel behind a a door when it is open. We have many times put one in a bedroom behind the door. The only time you will see it is when the door is shut. Even then you an put a cabinet door to make it look nice.
 
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Old 05-01-11, 09:59 AM
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The house being a duplex, access would be an important consideration. Couldn't have subpanel for tenant B in my closet, for instance, correct?
 
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Old 05-01-11, 10:21 AM
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Correct. They are required to have access unless there is "building supervision". IE: Somebody to provide access such as you on site or on call 24/7.
 
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Old 05-01-11, 10:50 AM
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This has been incredibly helpful.

Thanks for your time everyone.
 
 

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