Curious, is the allowance higher because Canada is cooler?
Funny, BTW.......
Canada has developed different insulation types and standards at the same time as the USA. Some examples:
USA VS Canada
THHN PVC/Nylon single conductor - in Conduit - commonly used = T90 PVC/Nylon single conductor (same specs as THHN) - in Conduit - rarely used
XHHW XLP single conductor - in conduit - rarely used = RW90 XLP - thinner insulation 600V, RWU XLP thicker insulation - in conduit - commonly used
NM-B THHN conductors, PVC jacket - commonly used residential = NMD XLP conductors PVC jacket - commonly used residential
MC/AC90 - metal clad, Various conductors, Alum or steel armour - with or without PVC - Not common with PVC jacket - no conduit required =
Teck90/AC90 VERY common XLP conductors Alum armour. PVC jacket on Teck. No conduit required - used extensively in Resi and comm/ind
Different regions and applications may differ from the above - but it's a good generalization
Yes, there are significant differences in terms of cold temperature rating. The 90 degree rating on NMD90 has to do with the copper temperature. In the specifications, there will also be a cold temperature rating. For *most* outdoor rated cables, the rating in Canada is usually -40C, It's common in the USA to see -25C. Yes, the northern parts of Canada do see -40C, and in some cases (Like Fort McMurray AB) we would often see a -50C requirement. My part of Canada (southern Ontario) rarely sees below -25C. (lowest in the past 2 years was Friday, at -21C).
The temperature rating is the ability of the cable to safely operate at a specific conductor temperature, and the cable and connected equipment's capability to get rid of the heat.
BTW the 4 main ampacity charts of both the NEC and CEC were standardized about 6 years ago to a North American standard (Canada adopted the US charts), but the application of the different cables to the charts vary, due to the differences in cable
Disclosure: I have worked for several wire and cable manufacturers in past years.