I have today had a most interesting lesson that relates to this discussion.
I work for a company that manufactures and distributes switchboards and componentry, including fuselinks. We have just received a shipment of fuselinks from a new supplier, and my job was to quality check them. One of the things that I got to check was how close to the published time/current curves these fuses were.
15A fuses were tested, firstly at 40A (near-instant blow), then at 30A (22Secs), then at 25A (11m 40s), then finally at 20A (> 4 hrs). These were very much according to expectations. The interesting thing was just how hot the fuse got at 20A. The whole office smelt strongly of frying fuse!The fuse was way too hot to touch, I would estimate it at around 120 deg C. Yet even after 4 hours of this torture, it was still hanging in there. I am told that this is entirely normal behaviour.
The point I am making here is that if the fuse board at the kick-off of this thread needed fan-cooling to stop the fuses from popping, they were not just passing rated current, but more probably a good 25% overload! Methinks that this cannot possibly be a good thing, no matter how you look at it.
