[mhennessy]

I must admit that the notion of burying a Polyswitch in the windings of a transformer is a new one on me. Is this actually done?

The only thermal fuses that I've seen embedded in transformer windings are the non-resettable types. On the face of it they seem like a bad idea, but every time I've met one that's gone open-circuit, it did so for good reason.

Littlefuse give data about derating for ambient temperature, but as their fundamental MO is self-heating, they don't appear to give any data about thermal resistance, which you'd need to know if you're hoping to conduct heat into them.

Ultimately, I can't work out if this is an incredibly smart bit of lateral thinking, or an awful bodge that is likely not supported by whoever makes the Polyswitch. Part of me wants to like it, but I feel that I'd need more information before I can make my mind up.