Multi-floor and 12/3

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  #1  
Old 04-24-12, 09:52 PM
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Multi-floor and 12/3

Hey guys, I have lurked for awhile, but now needing some help.

Basically I have a 100amp box that is getting to its limits, it is older and needs replaced. I have a pretty good understanding but I am still having someone replace the box for me.

Two questions I have.

I need two separate 20a plugs in my office. Any real issues running this on a 12/3 with the wide double poll breakers?

And the other question is how do I get this line into my office? I had a guy over once and he wanted to run it through conduit on the outside of the house. I would much rather do this internally for cosmetic reasons. Currently the lines in the attic are all 15a, besides a 20a A/C line that looks like it was added after the house was built, but I can't figure out how on earth they ran it. It almost looks like it is pulled off a plug in another room.

I didn't know if anyone had any real tricks to get a line from the box that is an in-wall unit in the garage, up through the second floor, into the attic and back down. Obviously the office into the attic isn't a problem, just the box to the attic.

Thanks in advance guys!

Z
 
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  #2  
Old 04-24-12, 10:49 PM
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Any real issues running this on a 12/3 with the wide double poll breakers?
A multiwire branch circuit must meet the requirements of Article 210 of the NEC. The applicable sections include:
To prevent inductive heating and reduce conductor impedance for fault currents, all multiwire branch-circuit conductors must originate from the same panelboard or distribution equipment [210.4(A)].
Multiwire branch circuits must supply only line-to-neutral loads [210.4(C)].
Since your application will meet both of these requirements, I see no need to invoke the exceptions:
Exception 1: A multiwire branch circuit can supply line-to-line utilization equipment, such as a range or dryer.
Exception 2: A multiwire branch circuit can supply both line-to-line and line-to-neutral loads if the circuit is protected by a device (multipole circuit breaker) that opens all ungrounded conductors of the multiwire branch circuit simultaneously (common internal trip) under a fault condition.
The requirement to use a common internal trip device (a double pole breaker) only appears in that exception and only applies to a multiwire branch circuit that supplies both line-to-line and line-to-neutral loads.

Taking Article 210 in its entirety, then, I would not install a DP breaker to protect this cable - except for one little detail. Last time I checked, only GE was making an AFCI breaker that did not contain some GFCI technology, and could therefore be used to protect an ungrounded conductor in a multiwire branch circuit. Since all DP AFCI breakers will hold on a circuit with a shared neutral, that's what you might need to install.

----------

Source for the NEC information: Branch Circuits - Part One, by Mike Holt, NEC Consultant
 
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Old 04-24-12, 10:53 PM
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I didn't know if anyone had any real tricks to get a line from the box that is an in-wall unit in the garage, up through the second floor, into the attic and back down.
What does the second-floor wall between the garage and the attic look like?
 
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Old 04-25-12, 10:04 AM
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Thank you Nashkat1 for your replies. The only reason I was thinking of doing the double poll is because I want two outlets with their own 20amp line, and I was just more concerned about someone turning off the breaker and thinking they killed the outlet, but the other one is still hot.

Basically each outlet will be running computer equipment and each outlet will need to support a 20a load for the UPS, and their are two of them.

As far as wall type, can you tell me what you mean and/or how to check? It is an exterior wall, brick up the first floor and turns to hardy plank on the second on the outside. I thought about trying to drill up and fishing, but the problem is I don't know how they separated the floors, so no telling how hard it would be to get through. The house was built in 86, and the did some cheap stuff, so It might not be that hard, just scared about hitting a water pipe or something.

Thanks again,

Z
 
  #5  
Old 04-25-12, 10:22 AM
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For a house built in 1986 they would have used platform construction. You can google for an image.

You will also have insulation in the exterior walls that will complicate the fishing. Pulling in the cable may create cold spots from where the insulation gets bunched up.
 
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Old 04-25-12, 02:33 PM
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You're welcome. First of all, a further thought on the code: Given that you are supplying two line-to-neutral devices with this mwbc (multiwire branch circuit), I don't think Article 210 requires a common internal trip device. But all breakers protecting a mwbc need to have a common means of disconnect. If I'm right, that means that two SP SFCI breakers with a handle tie between their handles might be better than one 20A DP breaker for your application. They might be less expensive too.

Basically each outlet will be running computer equipment and each outlet will need to support a 20a load for the UPS, and their are two of them.
A 20A load on each circuit? Have you checked the data plates on everything, or plugged everything into 1 power strip and amp-clamped the cord of the power strip? !,920W is a lot of draw.

As far as wall type, can you tell me what you mean and/or how to check? It is an exterior wall, brick up the first floor and turns to hardy plank on the second on the outside. I thought about trying to drill up and fishing, but the problem is I don't know how they separated the floors, so no telling how hard it would be to get through. The house was built in 86, and the did some cheap stuff, so It might not be that hard, just scared about hitting a water pipe or something.
I think that's good enough for now. tHANK YOU.

If it's standard framing (platform framing, as pcboss suggested), there should be little problem punching through, provided you stay between the joists. In fact, there may be a bunch of wires running up to the attic along that path now. I'd go have a look at the top of the second-floor wall in the attic, directly above the panel.

Even if there aren't wires emerging into the attic now, you will likely find several making their through the garage ceiling/second level floor assembly when you open the wall above the panel and look. If so, then you should be able to go on to the attic. There might be a fire block across the stud bay about half-way up that you'll have to punch through.

This exterior wall shouldn't have any plumbing in it. Maybe one electrical cable running horizontally, but that shouldn't be a problem. There are scanners that will help you "see" what's in the wall before you open it. The MultiScanner® Pro SL from Zircon is the one I use. Note that this scanner, and most scanners like this, will only detect non-ferrous metal pipes - i.e., copper pipes - and will only sense an electrical cable if it's actively supplying a load.
 
  #7  
Old 04-25-12, 02:55 PM
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Do you have a basement or crawlspace? Usually exterior walls are difficult to fish because of the insulation. A common way to fish on the interior of the house is up a hallway wall or inside a closet if you're lucky enough to have two closets stacked on top of each other. Even if you need to cut a bit of drywall, it's much easier to patch a closet that you'll never see than the middle of a wall in an open room.
 
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Old 04-25-12, 03:17 PM
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@Zorfdt:
The OP's panel is mounted in an exterior wall in his garage. Slab below, most likely.
 
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