jwinkler JL how many curcuits are on that breaker? what amperage is it? If you over power that breaker you will have it go on and off from the load (amps) being to much. This will smoke the connections in the fuse holder. When the load to the fan kicks on, first the spikes amperage, then the steady pull on the curcuit, The contacts in the fuse holder get hot and spread apart. More resistance happens and you have melted wiring. I also hope there is a fan relay for turning on and off the fans. 30 amp is ok 40 amp would be better. I have 2 of the fuse holders you are showing. I use one for each of my fuel pumps in the car. Even though the wiring is heavy the contacts are light duty in the plastic. IMO I wouldn't run more than a 20 amp curcuit to one accessory with these holders. Yes I have melted them too. Yes I did stay at a holiday inn and work under the 1/8 moon shining, repairing a wiring harness for a friend. Old days no problem with that fuse holder, today cheap metal for the contacts. Some contacts are only copper coated, not solid.
Rick L.