electrical, temperature rating of romex
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The b in NM-b means the conductors contained within are rated 90degrees C. However, this limitation is to be used only when derating the ampacity of a conductor. Actual ampacities are based on 60degrees C.
This information is available in the National Electrical Code, Article 336 -NONMETALLIC-SHEATHED CABLE
This information is available in the National Electrical Code, Article 336 -NONMETALLIC-SHEATHED CABLE