Just because the NM has 3 conductors does not make them all CCC. The ground only carries current in the event of a fault. Also remember that you are using the 90 degree values and dearting from there.
Counting the outlets is almost meaningless. Just because you have the ability to plug in does not add any load to the circuit. Likewise measuring the ampacity on loads that can be transient in nature does not give a true picture. For example, adding a 12 amp vacuum to a circuit that normally carries 4 amps. Are you now going to say it is overloaded?
Even with derating those cables are fine. The rule is that when a hole is fire or draft stopped and has multiple NM cables then the cables are subject to derating based on T310.15(B)(2)(a). There is no rule that says you can only have one, two, three or four cables or ten NM cables per hole. . If there is no fire or draft stop then there is no limit to the number of cables going through a hole in a stud. In fact the number of cables is really irrelevant since it’s the number of current carrying conductors (CCC’s) that matters. In most instances that means that up to 4-14/3 or 4-12/3 NM cables can be installed in a hole that fire or draft stopped. That’s because either of those groups of cables would be only 8 CCC’s and derating at 70% still wouldn’t change the normal ampacity of those cables.
Ex:
4-12/3 home run cables in a fire stopped hole equals 8 CCC’s (neutrals are not considered CCC’s in this application) {310.15(B)(4)(a)} #12 (90° C conductor) {334.80} = 30 amps {310.16}
30 amps * 70% = 21 amps derated ampacity.
So the 4-12/3 NM cables, even though they’re in a fire stopped hole, still can be used at their normal ampacity of 20 amps.
So back to the original photo. It doesn’t appear that any hole has more than 6 CCC’s so derating, even when applied, does not affect the normal ampacity of the NM cables.
Good post Robert, I was thinking the real ampacity of 12 gauge wire was more than 20 even though the NEC decided to use 20. Same with 14 gauge, the manufacture rates it at 20 amps but the NEC decided to use 15 amps.
Are you sure that using the 90 degree rating is correct?
I never consider the ground a CCC. I was referring to the two hots and a neutral within the cable. I count the neutral because there is never a truly balanced load.
As for the number of outlets and amp measuring, I forgot to add the smart ***** smiley (rolling of eyes) at the end of the statement. Meaning that it IS meaningless as well as beyond our scope.
Yes, the 90 degree ampacity is permitted for derating of NM cable. It was in the original post, 334.80.
Nope, it’s only 8 CCC’s. The code reference was in the original post. 310.15(B)(4)(a).
So a three wire, multi-wire branch circuit (MWBC) with two hot legs on opposite phases and a shared neutral conductor would only count as two CCC’s for derating purposes.
OK, then I have something like this. Home built in 2003.
Question 1. There was a side vent stove added and the duct runs between the joist and in the proximity of the cables. About 1-1/4" clearance between the cables and the double-wall flue. (The sideways picture)
Question 2. There are definitely more than two cables going through the I-joist. Along with the NM Cable. These cables DO NOT penetrate any fire blocking. They run horizontally across the finished basement ceiling.
Question 3. Along with the NM cables, the uninsulated GEC and multiple cable TV Coax cables are sharing sharing the same hole.
The cables were** bundled for about 30 feet** from the service panel all the way across the basement.
I did a little more research and picked up Wiring Simplified 42nd Edition and on Page 123 there was mention about not being able to put more than 4 cables through a common set of holes based on NEC 310.15(B)(2)(a) and 240.4(B)(1)
