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WDESHOTEL 04-14-2007 02:45 PM

Replacing a Interior Main Panel Box
I am remodeling my house, and I am changing my main panel inside to a 200 amp panel. I know generally all the circuits from the attic is run through holes that are drilled through the top plate and come through the top of the panel where they are secured with nm-b romex clamps. I want to know if there is anything against drilling 2-2.5" inch holes through the top plate and install 2 - 2" male adapters and srew them to secure them to the top of the panel box and run short lengths (16") of 2" sch80 pipe down through the holes of the top plate and into the male adapter and the pipe would be flushed with the top plate, that way all the wires would not be exposed in the wall and this would also allow me to add more circuits if I need them later more easily. The wires would be secured before entering the pipe.

jwhite 04-15-2007 06:16 AM

If as a result of using the conduit the cables end up bundled together for 24 inchs or more you would need to start doing de-rating calculations to see if the wires would have to be larger than they are now. That is 24 inches of cable bundled to gether, not 24 inchs of conduit. Since your conduit is only 16 inches you will probably have them seperated soon enough to not worry.

De-rating starts with 4 current carrying conductors. For this we count all the wires that are not grounds, not the cables. So a 12-3 w/g and a 14-2 w/g would be 5 CCCs. For circuits up to 30 amps (number 10 wire) do not worry at 9 CCCs and worry (begin to do the math to be sure) when you get to 10 CCCs.

WDESHOTEL 04-15-2007 08:55 AM

Thanks jwhite, but I am still a little confused on the definition of bundeling on exactly what that means. Lets say the conduit is 24" long and I have 10 12-2/wgnd circuits going through the conduit and naturally the circuit wires are not all tightly together with tie raps withing the pipe. The wires are separated within the pipe, Is this still considered bundeling? Please Advise.

I guess what I am consider bundeling is when all the circuits are secured together and are physically touching each other with tie raps every so often, then this is bundeling the cables together.


jwhite 04-15-2007 09:13 AM

If you have 10 each 12-2 circcuits you would have 20 current carrying conductors. Yes inside the same condduit is considered bundling even if you ran a 6 inch conduit, as you cannot strap the cables to insure that they remain seperated.

Table 310.15 (B) (2) (a) says that you would need to derate the cables to 50 percent.

Table 310.16 says that number 10 at 90 deg c is 40 amps and 50 percent of that is 20 amps, so all your 20 amp circuit woud have to be number 10 wire.

Romex can never be installed using anything but the 60 deg columb, but you can start your de-rating calculations at the 90 deg columb.

Bundling can also happen if you run your cable in boored holes in the floor. For example you have several floor joists boored out for running wire. You run the cables together through several holes before branching out in different directions. If you do nothing to secure the cables between boored holes and insure they remain seperated, then they are bundled along the entire run, not just where they pass through the holes.

WDESHOTEL 04-15-2007 09:50 AM

ok, jwhite. how would you run wires in a attic that is in a neat manner and not just running every which way on top of the ceiling joist? Are the 3m cable stackers a acceptacle alternative?

ok I have another technical question that is off the wall. When derating was figured, was this at full load and by that I mean if you have a 12-2 w/gnd that has a max. current capacity of 20 amps and the load is such that it draws 20 amps, then due to the effect of heat that is generated then the derating occurs. What if I have 3 12-2 w/ gnd circuits running through bored holes in ceiling joist and the max current draw on any one of the circuits is 3 amps. Would derating occur or is derating no matter what the draw is on the circuit?

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