This particular image is of a fuse block of tiny little KTK-30 amp fuses, 480V. It feeds a lighting ciruit in our plant. We see a fair amount of this in our plant, and I've never been able to figure out what is the origin of this anomoly. What component is at fault here, the fuse? the fuse clip? the wire?

Is it possible that there is an internal connection in the fuse itself that is bad? Maybe between the fusing element and the fuse cap? At first glance it appears that there is a bad connection between the fuse cap and the fuse clip. But I don't know if I trust that. In the past, we've changed fuses, changed fuse blocks and clips, wires, connectors, etc. and these problems seem to come and go. I can't make sense out of them.

Anybody else been having any similar results or experiences?

Lighting_Contactor_4_Panel_6-7.doc (238 Kb, 32 downloads)

Bill,

One simple technique to help sort things out is to take the same fuse and flip it end for end. If the hotspot follows, it suggests the fuse. If not, it suggest the clip or or connection. Careful measurements of voltage drops/resistance may also help isolate the problem.

From this image I doubt it is the fuse, but try flipping it. Fuses are weird in that each can have unique thermal signatures, even the same brand/type/size but that is another posting!

I would caution that you are dealing with temperatures that are quite high for this type of equipment. The fuse clip, for instance, begins to anneal at 100C after about a month. At that point it had begun to lose it's the spring qualities that make it work so it begins to heat more. Of course, as it heats resistance also increases which, again, results in more heating. At that point it can reach "runaway" stage quickly.

Generally at these sorts of temperatures it may be best to just change out the whole fuse block.