Spin the barrel!

Loose connections, and improper use of equipment could be cited here!

What's the voltage?
The remaining KO rings should be supplemented by a bonding bushing if it is over 250 volts to ground. (per 250.97)
It would be a good idea at any voltage.

Another case of a "bad connection/contact"
Probably started at the load lug. Second guess is metal fatigue at the load side fuse clips, causing 'heating scenario.
Solution, new disconnect, fuses, and possibly replace the load wiring. That is: after determining the load info. BTW: 480 volt???
John

Don’t forget that it might be 600V at the right latitude.

Suppose an AC "millivolt-drop" test on Aø with a power-rated voltmeter would be guaranteed off scale here.

It's worth noting that plastic and rubber cable insulation gets rock hard {or turns into conductive carbon} with any significant time in this condition.


[This message has been edited by Bjarney (edited 01-20-2003).]

Why does the center fuse look too short? It is only half in the bottom clip. Is it the wrong fuse?
Could that be what happened to the fuse on the left? It looks like the same type.

[This message has been edited by jdevlin (edited 01-20-2003).]

jdev — The center fuse has a universal "rejection" notch included with all NEC/UL class-R ferrule fuses. These days, it's just about impossible to find replacement fuses without that feature, and class-R fuses are, in most all cases, considered an acceptable replacement for class-H and class-K fuses.

I see the notch now. I don't work with that type of fuse. It is new to me.

Had this happen in a 400 amp disconnect on a 208 volt service to a 7-11 (convenience store). The fuse clip, wire lug, and about two inches of 500 kcmil copper all melted into a puddle in the bottom of the can, along with a pile of sand. The fusible element was 100% intact.

Cubby:
Sounds like a fuse fail at the link to ferrule joint/connection. Gets hot as hell from the arcing (internal) heats the spring clips, deteriorates them eventually, then the wire/lug heat & deteriorate and poof...a meltdown.
An IR scanner (cheap ones available now) shows most hot spots, and is a good investment isf you can get the clients to do it.

BTW, Bussman may be interested in the "failed" fuse if you have it. I have a Bussman Fuseologist around here, and he loves to get burnouts for his lab.
John

What's the rejection notch for? How's it supposed to work? Do some fuse holders have some sort of protrusion that's supposed to fit into these things?

HotLine1:
It's been a dozen or so years since this happened, and being as there was nothing left of the connection, fuse clip, or ferrule, I don't exactly know what the mode of failure was. I suspect you are correct. I may still have this in my "collection", I'll look this weekend. BTW, I now have IR equipment.

SvenNYC,
Yes, Class R fuseholders have the rejection feature to prevent the insertion of a Class H fuse, which only has a 10k aic (interrupting rating).

Ed