I would have limited that to 2-cc in a cable, which probably most NM installs are.
There are the public comments
here for WAC the rule change. Seems that the manufactures supported the rule change, hopefully we will see it in the next NEC.
Thats a interesting read,
comment #1 I don't think makes any sense, and contains an error in the commenters math they use 250 Volts, as you always use standard voltages in calculations, 220.5(A)
Comment #2 is basically no comment:
BIAW represents over 8,000 member
companies within the residential
construction industry in Washington state.
We don't have comments on a specific
rule change being proposed today.
Comment #3: says
Have there been studies published
documenting the safety standards of the
increased temperature rating of the
cables in question? Are those studies
available for review and comment?
And the agency response is basically;
since the NEC allows a temperature rating of 75°C, for wire sizes #8 AWG and larger for others cables then it should be fine for NM.
The flaw in that is they are making the assumption
all UL cable standards require UL-83, the conductors in NM-B cable are not required to meet UL-83 they way MC , SE, SE-R , Tray cable do. And the way the UL standard for NM cable UL-719 section 8.1(b)(1) reads to me it still allows 'TW construction' in NM-B even with the -B marking. However the argument in favor of 75
°C has some merit as the UL 719 says PVC insulation should hold up to 90
° C I guess time will tell.
There was a interesting PI for the 2026 proposing a even less permissive change that was rejected, I wonder if they were tracking on that?
It was:
Public Comment No. 1609-NFPA 70-2024 [ Section No. 334.80(A) ]
(A) General.
The ampacity of Types NM and NMC cable shall be determined in accordance with 310.14. The ampacity shall not exceed that of a 60°C (140°F) rated conductor. The 90°C (194°F) rating shall be permitted to be used for ampacity adjustment and correction calculations, or for termination requirements, provided the final calculated ampacity does not exceed that of a 60°C (140°F) rated conductor. The ampacity of Types NM and NMC cable installed in cable trays shall be determined in accordance with 392.80(A).
This would have allowed the use of NM-B with equipment that has termination 75
°C, in recognition of the 90
° C rated conductors within the NM cable, without changing the overall limit of NM cable to the 60
° C ampacity and that fell of deaf ears, becasue of the lack of a UL standard supporting this.
This would have allowed a 48A continuous load on 6/2 NM installed with a 60A breaker with 75
°C, rated terminations, and supplied by NM cable. Since the way 210.19(A)(1)(a) / (b), 240.4, 334.80(A), play together and since ampacity of a 6/2 NM cable is limited to 55A and with the 60A OCPD
The 6/2 NM cable meets 210.19(A)(1)(b), as its 55A ampacity exceeds the load of 48A. It also complies with 240.4(B) required by 210.20, as that is next standard OCPD size larger than its ampacity of 55A.
The catch then is 210.19(A)(1)(a), which calls for a conductor with an ampacity of 60A before ampacity adjustment and correction.
I propose a few alternate options
1) Allow Tray cable to be used anywhere NM is. It would be a small change on Article 336 on Tray cable, section 336.10(9) and allow the new 'Joist Pull' tray cable type TC-ER-JP tray cable to be used as power cable in any locations permitted in 334.10 and allow the tray cable to use the 75C ampacity, as the UL standard does require the conductors in tray cable to be UL-83 THHN. If its ok for a generator its ok for any 75C termination and it does not matter if control conductors are present.
2) Accurately model / test 2CC in a raceway or cable, replace 310.12 the dwelling service/feeder table with a real 2-cc in raceway or cable table in 310. The 310.12 Is based on old 1956 research there there is less heating from 2 CC's, with all the tech we have not it should not be hard to model that for a 2-conductor installs such as 6/2 NM cable.
