Had a case this morning where I had a 50 amp FRS-R fuse in a GE 60amp disconnect fail. I was not around when it occured however by all indications it really "blew"
. The top was burned out of the fuse and the line conductors above it had the insulation charred. the Red arc sheild was melted and sagging. These fuses are on a air compressor motor and normal amp draw is 29amps free running and 31amps under full load. I replaced the burnt conductors and checked out everything else. There were no line to ground faults and the resistance on the motor windings all check out normal. I replaced the fuse and fired up the machine everything ran normal.
What are the chances of a fuse failing like that for no apparent reason except for being a defective fuse? This compressor with these fuses has been in service for 3-1/2 years with no problems.
This incident also just reinforced in my mind the importance of have all open knockouts plugged and using the appropriate enclosure for the enviroment (dust etc). With the fire that blown fuse must have created, It would have been an ideal source of fire had it not been contained inside a proper enclosure.