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Joined: Mar 2001
Posts: 333
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Earl, I can see your stance for multiple joists being drilled and the cables running through them all. My posts were towards the original post, which sounded like the cables only shared 1 hole at the plates above the panel.
steve
Steve
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Joined: Apr 2002
Posts: 178
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Earl how can you justify your interpitations based on...cables must be stacked or bundled for more than 24" before derating shall be enforced? Bored holes through wood framing are usually less than 24".If in fact we come through a hole and the wires aren`t bound together and are separated even if slightly they are separated and are not bundled for more than 24" sorry I just don`t get how they could be consitered bundled Can someone define bundled
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Joined: Dec 2003
Posts: 751
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That's just it. Bundling is not really defined, and, as someone pointed out, bundling is equated to running in a conduit. But what about the size of the conduit? Wouldn't 6 #12s in a two inch conduit have enough room to shed heat? At the least much more than the same 6 #12s in a 1/2 inch conduit. It is this lack of differentiation that leads me (and other inspectors) to err on the side of caution and intrepret installing cables in bored holes further than 24 inches as bundling.
Cheer up, as I stated earlier, you can run 4 cables in all your holes. When you do the math, the derated cables meet code. #14s go to 15 amp breakers, #12s go to 20 amp breakers, and #10s go to 30 amp breakers.
Most electricians will use a 7/8 inch drill bit to limit this automatically.(it's tough to force 5 NM cables into the hole) And, when drilling 2 x 4 studs, the hole will be centered 1-1/4 inch back from either edge. (1/8 inch fudge factor)
Earl
Earl
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Joined: Sep 2003
Posts: 650
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Just addressing the '6 #14 in a 2" conduit versus 6 #2s in the same conduit'...
A while back I spent some time figuring the heat dissipation from conductors at their maximum current rating. The interesting thing is that the heat produced per unit length goes up very slowly as the wires get bigger.
Simply take the current squared and multiply by ohms per foot:
wire 60C A mO/ft Watt/ft
14ga 20 3.07 1.228 (note 240.4(D) )
10ga 30 1.21 1.089
6ga 55 0.491 1.485
2ga 95 0.194 1.751
All of the heat generated has to leave the conduit, so it doesn't matter if the wires are small relative to the conduit size or large relative to the conduit size; all that matters is that the total heat produced in the conduit is suitably low.
-Jon
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Joined: May 2004
Posts: 28
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NEC Article 520-2. Definitions. Bundled. Cables or conductors that are physically tied, wrapped, taped, or otherwise periodically bound together.
this is what i found in my 99nec..02 is with a friend.... so depending on ones IQ, there could probably be 36,482 definitions of bundling or more! LOL...NEC needs to address this big time, as well as many many other issues in the NEC ...why not put the def. of bundled/bundling in the front with the others?
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Joined: Feb 2002
Posts: 375
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winnie ----
I use different numbers:
wire 60C A mO/ft Watt/ft
14ga 15 3.13 0.70
12ga 20 1.98 0.79
6ga 50 0.49 1.23
4ga 66 0.31 1.35 (66 is a strange amp)
2" PVC conduit dissipates 12.1 watt/ft (based on 15 4ga - 9 current carrying)
This allows (current carrying conductors) 17 14ga, 15 12ga, or 10 6ga (based on heat dissipation) WITH NO DERATING FROM THE ABOVE AMPS.
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Joined: Mar 2001
Posts: 2,056
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Those interested in this topic should obtain a copy of the September/October 2003 issue of IAEI magazine.
A study was done with several cables routed through a double 2 x 4 stud plate and an additional 1 x 4 (total thickness 3 1/2") and loaded from 60 to 80% ampacities.
Throughout the day, depending on outdoor temperatures, the temperature rise of the conductors exceeded the allowable temperatures of the NM cables.
The results more involved than I can go into right now, but maybe someone can obtain permission to reprint the article.
It's interesting stuff.
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Joined: Feb 2002
Posts: 375
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Redsy ---
My residence (2000sqft, 200amp) houses my wife's business. The load include 6 computers and electric heat.
The 8 hour load is less than 34amp @120 volt (about 4KW).
If that load were on only 3 20amp circuits, the circuits would be loaded to only 50%.
I think that loading used in the tests might be a bit high for residences.
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Posts: 806
Joined: October 2004
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