Sounds like insulation categories, as well. Insulation for motors, anyway. I probably should have googled before I replied, but it goes along the lines of;
Whatever category of insulation you have, lets say 125C, which will be represented by a letter, approximately category E or F, or something along those lines here. It will quite happily do 125C all day long, for a quantifiable amount of time. But for every 10c above this rating, it will roughly halve its expected lifetime. So, lets say our 125C insulation is rated to last for 10,000 hours, as a pure pulled-from-the-arse number. If we run it at 135C, we can roughly halve its lifespan to 5,000 hours. 145C, you can kiss it goodbye after 2,500 hours. And I'm pretty sure that there will eventually be a point where some very interesting properties of that insulation come to light in a rather... lets say, luminous way.
It sounds much like what the above members have said. Again, I am still a major in electronics noobery, so take what I say with a grain of salt, and please do feel free to learn me something if I get something wrong - I am here to learn, after all. But as far as motors go, the wiring is essentially a consumable part in decently industrial cases. For example when a train goes in for an overhaul roughly every 10 years, they'll basically strip the train down to its shell, remove all of the traction package components, and part of this overhaul will be ripping the motors apart, discarding all of the wiring that makes up that motor, renewing the wiring looms, re-assembling the traction package back on to the train, and hey presto, your six car train has 16 nicely refurbished motors ready for another 10 years of service and roughly 10 million kilometres, until the next overhaul.
TL;DR, if the motor becomes large and expensive enough, it's my understanding that the wiring becomes consumable service items that have to be replaced every so often. But these are motors that will see daily service for many decades, so it makes economic sense to do this.
Hope this rambling diatribe is remotely entertaining to anyone to read!
Cheers,
Rory