Damage appears to be on the line side of the fuse, possibly a line to ground fault. Or, severe overheating condition within the switching mechanism. Note there appears to be no damage on the load side terminations, or the load side of the fuse.

Every fuse has a limit of how many amps it can safely interrupt. Exceed that, and this is what happens.

All it takes is a dead short - and more fault current available than the fuse is rated to interrupt. That's what all those 'fuse classes' are all about.

It's possible that the wrong type of fuse was used, but more likely that the fuseholder selection itself wasn't correct.

It's also possible that the PoCo made some changes - a new transformer, etc., that led to more current being available then there was before.

The AIC rating will affect the safety blow thru the fuse so if the system was upgraded the AIC will go up and the fuse stay the same good chance it will really blow apart like you see at the photo ditto with breakers


I know Bussman fuse company did have a link or chart for AIC rating and it is good details in there.

Merci,Marc

Marc:

Bussmann Fuse has a wealth of info available...

www.bussmann.com

They have a few really good videos of fault current testing. Also, the 'Safety Basics' materials are informative and interesting.

I have seen heat related causes where a poor connection destroyed the fuse but never exceeded the ampere rating of the fuse. The tube is consumed over time from heating usually at the ferrule ends and eventually the guts get exposed. A fault cannot clear because all the arc quenching material has fallen out. The fact that the fuse tube is consumed on the top is part of my guess and i would look for silica sand in the bottom of the fuse holder to bolster or kill my theory. Also look for heat blued conductor or insulation damage like melting at the terminals. A Fault seldom causes slow failures and this looks like a heat failure with a fault at the end.