We have a halogen oven in our plant that is powered by 480volts. It is a pretty basic setup. The line feeding it is protected by a 125 amp breaker. All the legs going to the halogen lights are protected by fuses. There are 5 small circulating fans on this oven and each leg of each of the fans is fuse protected (15 fuses).
My problem is this:
Last night during normal operation the 3 3amp fuses on circulating fan #4 failed. They literally exploded and burned up. It tripped the 125 amp breaker feeding the oven. No other fuses or OL's were blown or tripped.

This morning I and another LE were investigating and we simply could not find the cause. No short circuits, nothing. We replaced the fuse blocks and the fuses and turned it back on and everything is running normal.
I am still puzzeled over why this happened. The fuses were Bussman Low peak LP-CC 3a 600v class CC time delay fuses with an A.I.R. of 20k.

I replaced them with fuses with Ferraz Shawmut "amp-trap" ATDR fuses with a rating of 200k.
I figured the rating was not high enough on the original fuses or they would not have exploded.

I know I did not go into a lot of detail here but Does anyone have any ideas what could have been the real problem ?

Also would it be unreasonable to expect the oven manufacturer to have put in fuses with a 200k rating rather then the 20 k.?