Paul:
For quite some time here in the US, the common door chime/door bell transformers were made to deliberately burn open the primary winding as a fail-safe. They were not supposed to get so hot as to ignie anything, but the end result would still be very hot to the touch.
I think now more of these transformers have the themal one-time fuse imbedded in them, IIRC some areas require them as a local admendment to NEC.
And my days spent servicing CCTV gear, the early plug-in transformers had no fuses and would literally go up in flames if shorted. (I metered one once, normal output at 24vac was one amp max, shorted it was pushing over 8 amps as it burned up!!)
