Not sure how old the fans were that he investigated, but i remember that thermal fuse wire being added back in the late 70s when I worked for a Nutone distributor. That issue was somewhat unique to SP motors used on vent fans, because it was implied that the fans would be moving air across them and keep them cool. Before adding the fuse link, the thought was that if you turned on a vent fan and it didn't vent the air, you investigated and fixed it. but people kept ignoring them and some caught on fire, so UL added the requirement for the fuse link, maybe around 1978? That issue would not likely happen in a pond pump surrounded by water. I had mine stop pumping and found out that my wife turned it on and left it on, for maybe 3 weeks before remembering to tell me about it. It just had a little stick in the impeller, I removed it and it started pumping again.
