Melted fuse

I have a 2001 bobcat 773 that i use around the farm. The blower motor for the heater recently quit so i first checked the fuses. It was a 25 amp fuse and that is whats supposed to be there. As seen in the photos the fuse not only melted but part of the fuse box as well. I assume i need to replace the fuse box but is there other things i should check as well? Why do you think this happened? The blower motor has worked great for the last 100 plus hours? Electrical is not my favorite task. I have a volt meter but not exactly sure how to use it correctly. Thanks for any help.

Resistance will cause heat. A loose connection with the fuse can cause it to heat up but not blow.

Once in a while it is reasonable to look at the fuse box. Beginnings of heat damage can be seen, and action taken to clean up and polish the grippers, and replace the heated fuse. Jim

That 15 amp fuse isn't looking too healthy either.

Looks like a bad connection to me which creates heat. Looks like the left side of the 15 below it might be heating up too.

(quoted from post at 23:19:58 01/02/20) I have a 2001 bobcat 773 that i use around the farm. The blower motor for the heater recently quit so i first checked the fuses. It was a 25 amp fuse and that is whats supposed to be there. As seen in the photos the fuse not only melted but part of the fuse box as well. I assume i need to replace the fuse box but is there other things i should check as well? Why do you think this happened? The blower motor has worked great for the last 100 plus hours? Electrical is not my favorite task. I have a volt meter but not exactly sure how to use it correctly. Thanks for any help.
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If you don't want to shell out BIG bucks for a new fusebox (and likely the wiring harness it's attached to), simply connect a single ATO fuseholder to the wires that lead to the poor connection melted fuse contacts and tuck it out of harm's way.

Blower motors are notorious for doing that.

They pull high amps, especially when operated on high for extended times.

Often the motor will begin to draw more amps as the shaft bushings wear and the lubrication dries out. It may be time for a new motor, especially if it is rattling or squealing. Dropping it back to a lower speed will greatly reduce the amp draw.

What you can try to do on the bad fuse holder, take the fuse block out, turn it over. Working from the back side, find the wire that feeds the blower, cut it loose from the burned out terminal. Buy a heavy duty fuse pigtail from the auto supply. Look for the heaviest wire size you can find. Trim the wire back away from the heat damaged end, solder and heat shrink one wire of the fuse holder pigtail to that wire.

Then find the accessory feed wire that powers that circuit of the fuse block. Don't cut the wire loose because it probably feeds other circuits in the fuse block. Strip back the insulation and splice the other lead of the fuse holder to that wire with a good solder connection, tape it securely.

Route the fuse pigtail wires out from behind the fuse block, reinstall the fuse block so not to pinch the wires.

That happens when the contacts become corroded. If there was one ohm of resistance between the fusebox contact and the fuse, at only 10 amps that would be a whopping 100 watts heating up the fuse.

Although you can measure the resistance across each fuse to see what the contact resistance is, it's tricky to measure low resistance with a typical multimeter. Alternatively, you can energize each circuit and see if you can measure any voltage drop across the fuse for that circuit; if you see even a tenth of a volt, that's enough to be concerned about.

I wouldn't bother with multimeter checks, though. Pull each fuse and inspect its contacts. If you see bright scratch marks like you see on the unburned contact in your photo, then it should be fine.

That happens when the contacts become corroded.
X2. I would install an inline fuse. However some inline fuse holders are junk. They don't make a good connection and melt the fuse. For a blower, I may look for a circuit breaker. If necessary solder the blower wire to the breaker.
geo

When you get resistance in any connections, including blade fuses or the fuse holders, the I Squared R heat energy becomes significant and can melt plastic as shown in your pictures. Older components including fuse holders and even the fuse contacts themselves can develop oxidation and carbon IE resistance. Having owned RV's for 49 years I've seen fan or furnace blower motors begin to draw excess current (maybe bushings maybe electrical) even if not enough to blow fuse and if so they need replaced.

Its a job to replace that entire fuse assembly but from the looks of it that may be required. If not get into that bad circuit (ahead of and BEFORE the assembly) and patch a new fuse and holder to it. It would take an ammeter to measure current draw of the fan motor, but there's a chance it may be excessive. If not then resistance (oxidation or carbon) must have been the cause.

John T

It looks to me like your fuse panel is falling due to loose connections or corrosion.

My thoughts have already been pretty well covered. The only additional advise I can give you since ?Electrical isn?t my favorite task." Is to hire it done. There are people who do this for a living and consider it business as usual. A wise man once told me, "You should do the hard tasks first and hire out the impossible." Many times that has been good advise and saved countless hours and money. But it?s your time & money, so you need to do whatever best fits your needs.

If the fuse holder still holds the fuse tight it's easy to fix! Just take a piece of 100 grit sandpaper and double it and slide it back a forth in the contacts. Polish the fuse blades too. I would do all the other contacts as well. Good to go for another 10 years!