Why is #6 Copper NMB cable's ampacity restricted to the 60deg Celsius rating even though it's actual manufactured ratings are to 90deg Celsius? It's ratings match type SE cable's specs, and it manufactured and rated to 90deg Celsius. I could pull the THHN conductors out of the NMB cable, pull them into conduit and now, they are rated to 90deg Celsius. I have heard that it is the rating of the jacket, that limits it, however the NMB cable's 30mm PVC jacket is the same as the SE Cable's 30mm PVC jacket. I have yet, to find a valid reason to the limitation. Please provide some insight, I feel, this is a rather VALID concern for everyone involved, electricians, manufacturers, homeowners, business owners, suppliers. I also believe this limitation should be changed.