2026 NEC MN-B Cable Changes

T

trevorm

Member
Location
Central Washington
Occupation
Electrician
Our Washington codes (WAC) just adopted some very intersting changes with regard to NM-B cable ampacity:
080 Ampacity of Types NM and NMC cable carrying suffix letter "-B".
(8)(a) The ampacity of Types NM and NMC cable carrying suffix letter "-B" shall be determined in accordance with NEC 310.14.
(b) The ampacity of #10 AWG and smaller ungrounded conductors shall not exceed that of a 60°C (140°F) rated conductor.
(c) The ampacity of ungrounded conductors larger than #10 AWG shall not exceed that of a 75°C (167°F) rated conductor.

You can view the actual code here

So it appears we (at least in Washington) can now use the 75 degree column for NM-B cable ampacity for conductors larger than #10awg. My 2026 copy of the NEC is enroute in the mail. Now anyone that already has a copy can you confirm this change has been made in the NEC as well? This rule change in the Washington code was approved in December 2025 along with the adoption of the 2026 NEC.
 
trevorm said:
Our Washington codes (WAC) just adopted some very intersting changes with regard to NM-B cable ampacity:
080 Ampacity of Types NM and NMC cable carrying suffix letter "-B".
(8)(a) The ampacity of Types NM and NMC cable carrying suffix letter "-B" shall be determined in accordance with NEC 310.14.
(b) The ampacity of #10 AWG and smaller ungrounded conductors shall not exceed that of a 60°C (140°F) rated conductor.
(c) The ampacity of ungrounded conductors larger than #10 AWG shall not exceed that of a 75°C (167°F) rated conductor.

You can view the actual code here

So it appears we (at least in Washington) can now use the 75 degree column for NM-B cable ampacity for conductors larger than #10awg. My 2026 copy of the NEC is enroute in the mail. Now anyone that already has a copy can you confirm this change has been made in the NEC as well? This rule change in the Washington code was approved in December 2025 along with the adoption of the 2026 NEC.
Click to expand...
No change in the 2026 NEC

(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, 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).
Click to expand...
 
I welcome the change, being able to use the 75 degree column for nm-b #8 and #6 will be very helpful in some situations. I thought that state codes were supposed to be stricter than the NEC not relaxed such as in this case? Will be interesting how the local inspectors treat this since the NEC contradicts the State code.
 
WA has made many changes in the past to its Washington Administrative Code WAC 296-46B that ended up in the NEC. I was on many WAC code change committees and it’s a good process with inputs all across the industry. The final approval is by the electrical board, the chief electrical inspector is a non voting member. Currently stakeholders are being asked to apply to the committee for the 2026 code adoption.
In WA the WAC supersedes the NEC
 
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