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Wire insulations have different temperature ratings: 80°C 90°C 105°C 125°C 200°C

These ratings can result in different current ratings for the same wire gauge.

Are there ways to distinguish them by appearance? There are some wires that I came across that lack markings on it, so I cannot really tell.

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There is no place for mistake because it is matter of fir safety. So, unmarked wire take as lowest rate then calculating maximum current.

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  • \$\begingroup\$ Incidentally this is exactly how natural gas pipelines are operated with respect to pressure and steel grade. \$\endgroup\$
    – Bryan
    Jun 30 at 1:53
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You cannot tell just by looking at it.

You can distinguish silicone from everything else by feel, but that is about it. If you don't know you can probably assume PVC which is the most common and also the weakest temperature rating.

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  • \$\begingroup\$ I think PVC is the 105C insulation? that's intermediate \$\endgroup\$
    – HYQ
    Jun 30 at 4:39
  • \$\begingroup\$ @HYQ Where did you get those temperatures in your original post from? Are they actual temperature ratings for insulation? Or are they temperatures pulled from an ampacity table? Those temperature are for allowable maximum temperature for wire+insulation for specific applications. For example, silicone wire may be able to handle up to 200C just fine but if that's being used inside a wall, you don't want to allow it to actually get that hot. \$\endgroup\$
    – DKNguyen
    Jun 30 at 4:41
  • \$\begingroup\$ Some PVC insulation is only rated to 70C apparently (though all the ones I've used are 105C). There is also PE insulation only rated to 75C. \$\endgroup\$
    – DKNguyen
    Jun 30 at 4:44

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