Rather than get caught up in the chemistry of coatings, how about this:
1.The "T" stands for thermoplastic insulated cable.
2.A single "H" means the wire is heat resistant.
3."HH" means that the wire is heat resistant and can withstand a higher temperature. This wire can withstand heat up to 194 degrees Fahrenheit.
4.A "W" means that the wire is approved for damp and wet locations. This wire is also suitable for dry locations.
5.The "X" means the cable is made of a synthetic polymer that is flame-retardant.
6.The "N" is for the nylon coating that covers the wire insulation.
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