Caught my car on fire yesterday on the way home from a local car show. No major damage, got it out in time. My question is what causes a fuse to melt instead of blowing?

I re-wired the entire car with an AAW kit. Everything has been fine until a couple weeks ago. The radiator fans quit on me, so I pulled over and found that the fuse had melted, and then blown. I traced all the wiring to the relay and fans, and the only thing I could think of was I had disconnected a power wire from the tripolar a/c switch to the fan relay since the a/c compressor is fubared, and I thought maybe the terminal in the plug had made contact with a ground and caused the problem. So I plugged that back in, and have been fine since.

Yesterday I was almost home and smelled smoke; since I was only 3 houses away I hauled home asap, and by the time it made the driveway the fusebox was on fire. I used the quick disconnect on the battery and put the fire out.

It started at the fan fuse again, and the outer section of the fuse block that holds the fuses is badly melted and will have to be replaced. All the wiring is fine. My question is why this fuse is melting instead of blowing.

It is a 30 amp spade fuse, proper size for this system. I have checked multiple times all the relay and fan wiring, and it appears normal and perfect, no evidence of heating the wires. I'm thinking that the fan ground is insufficient, so I moved the #10 ground wire for the fans to the engine block.

Can this cause a fuse to melt instead of blowing? I really do not want a repeat.............. ;)

Jody

Jody the problem (short) has to be at the fuse block or fuse. Anything beyond that and the fuse would have blown providing the protection it's there for.

Jody the problem (short) has to be at the fuse block or fuse. Anything beyond that and the fuse would have blown providing the protection it's there for.


well, it's happened twice now, but the first time after it melted it blew, so no fire. Thought I'd corrected it, but the second time it caught the fuse block on fire.

The fuse block is two pieces that unsnap on the inside of the car, and a third section that plugs in from the engine side of the firewall. There are wires from the firewall terminal to the outer section of the fuse box, and they have terminals pressed in to hold the fuses. This section is what is damaged, but all the wires on the backside of the fuses are perfect, no discoloration, look brand new. Can't find any problems there.

Real curious as to what AAW says tomorrow when I call them.

Jody

I would run the fan and measure how many amps it draws. If it isn't blowing the fuse, it might be drawing just below the amps it takes to blow the fuse but enough to heat it up. A poor ground would limit the amp draw of the fan, a better ground might increase amps drawn thru the fuse.
I wonder if the fuse wires or connectors are not up to carrying 30 amps??? Whatever is most undersized, is going to get hot.
David

I would run the fan and measure how many amps it draws. If it isn't blowing the fuse, it might be drawing just below the amps it takes to blow the fuse but enough to heat it up. A poor ground would limit the amp draw of the fan, a better ground might increase amps drawn thru the fuse.
I wonder if the fuse wires or connectors are not up to carrying 30 amps??? Whatever is most undersized, is going to get hot.
David

the fan fuse is 30 amps, the power and grounds are 10 gauge as per their kit. I would assume (I know :D) that the wiring and terminals are sized correctly in their kit. I have a 60 amp relay as the twin fans require that, a standard 40 amp can't handle the kick on draw of the fans.

I've run the Mark VIII fan in several cars. They require a 70 amp relay as the startup draw is big. Never had any fuse or wiring issues, same size wires.

Jody

I think Dennis hit the nail on the head. An excess current draw would blow the fuse. If, say, the fuse itself was not making a good contact with its terminals in the fuse panel, that connection would heat up under load possibly enough to melt components and maybe even cause a fire without necessarily blowing the fuse.

I know Ford had a problem in the 80's with ignition switch connectors that would cause problems with intermittent connections and even fires according to their TSB. They came out with an improved connector to be spliced in that solved the problem. I never saw a fire, but replaced plenty of burnt looking connectors.

10ga wire should be plenty adequate for a 30 amp load. It sounds like your fan circuit is wired correctly. I agree with testing the actual current draw of the circuit. It will be difficult to autopsy a burnt fuse panel, but I think that is where the problem was.

I believe the suggestions given here as to the fusebox/fuseblock are correct. It could be the style/model of fuse holder.

ATO, ATM fuses rely on a tight fit into a formed socket, much like a quick disconnect terminals and the same with inline SFE fuses. Thirty amps through a Q/D is asking alot.

I would look for another style of fuseholder, i.e., power amp supply power type and solder the 10 AWG to the terminals, then install the fuse of you r amperage choice. I would also solder any of the fan supply/ground leads including their terminals.

As said, the fusebox is melting, this is where the heat is at, the connection. Do you see any damage to the wire fromt he fuse to the fan? The fan connection? Any melted insulation is a sign of heat, poor connection.

Jody do you have an ajustable thermostic? If so where is it located?Make sure the spade connectors on the side of it is not arcing off of some close by metal.Mind did this burnt the fuse and relays up.Had to replace fuse and wiring and relocate the adj thermostic.

I believe the suggestions given here as to the fusebox/fuseblock are correct. It could be the style/model of fuse holder.

ATO, ATM fuses rely on a tight fit into a formed socket, much like a quick disconnect terminals and the same with inline SFE fuses. Thirty amps through a Q/D is asking alot.

I would look for another style of fuseholder, i.e., power amp supply power type and solder the 10 AWG to the terminals, then install the fuse of you r amperage choice. I would also solder any of the fan supply/ground leads including their terminals.

As said, the fusebox is melting, this is where the heat is at, the connection. Do you see any damage to the wire fromt he fuse to the fan? The fan connection? Any melted insulation is a sign of heat, poor connection.

the wires at the fuseblock and terminals that held the fuse all look perfect, no damage or discoloration. I guess when I replace the outer plastic panel I could remove the fan terminals and replace with a heavier duty terminal/block separately, outside the fuseblock.

Jody

Jody do you have an ajustable thermostic? If so where is it located?Make sure the spade connectors on the side of it is not arcing off of some close by metal.Mind did this burnt the fuse and relays up.Had to replace fuse and wiring and relocate the adj thermostic.

no, the fan on/off is controlled through the BigStuff 3 computer. It handles the grounding of the relay to control the fans, and is adjustable to any on/off temps you want via a laptop.

Jody

well, called AAW, talked to Donny, and got my problem figured out. When I wired the car I wanted the relays inside under the dash. The AAW kit comes with an orange relay trigger wire from the fusebox, through the firewall, and to the front of the car for the fans. I used this for the #30 power terminal of the relay, instead of the #86 12 volt trigger terminal it should have been used for. This caused all the fan load at the relay to be run through the 30 amp fuse in the fuse box, basically eliminating the advantage of the relay completely. This is a good lesson as to the dangers for those of you who run electric fans without relays............... ;)

Stupid mistake that could have caused major damage, so I was lucky. I want to thank Donny at AAW for the excellent support. I may have to send the fusebox back as it's apparently pretty difficult to remove these double barbed terminals. I'm going to see if I can remove them, otherwise I have to remove the harness from the car :( and either have it repaired or replaced.

Jody

Can you identify the hotspot or source of the fire? If there was no wire damage, melted insulation, burnt terminal etc on the hot side of the fuse and it's holder I would be looking for a bad connection within the fuse block. Resistance creates heat, if the component created the resistance the fuse would blow. If there was a dead short I would think there would be signs of excessive heat on the hot side of the fuse wiring and even a blown fusible link. That really only leaves the the fuse block and the fuse as suspect. A cold solder or loose connection can create resistance and heat. I wouldn't expect an intermittent short within the fuse block itself and a dead short should have killed a fusible link.

Since you melted one fuse and then a replacement resulted in a fire I'm inclined to believe it's not the fuse itself but the fuse holder. It may not be properly connected at it's source within the fuse block. If you pull the fuse block off the firewall can the block be opened or is it sealed? If you can split the block apart you might find signs of the hotspot...

well, called AAW, talked to Donny, and got my problem figured out. When I wired the car I wanted the relays inside under the dash. The AAW kit comes with an orange relay trigger wire from the fusebox, through the firewall, and to the front of the car for the fans. I used this for the #30 power terminal of the relay, instead of the #86 12 volt trigger terminal it should have been used for. This caused all the fan load at the relay to be run through the 30 amp fuse in the fuse box, basically eliminating the advantage of the relay completely. This is a good lesson as to the dangers for those of you who run electric fans without relays............... ;)

Stupid mistake that could have caused major damage, so I was lucky. I want to thank Donny at AAW for the excellent support. I may have to send the fusebox back as it's apparently pretty difficult to remove these double barbed terminals. I'm going to see if I can remove them, otherwise I have to remove the harness from the car :( and either have it repaired or replaced.

Jody


You got this in as I was writing my previous reply... I have to ask then why the 30amp fuse didn't blow?

You got this in as I was writing my previous reply... I have to ask then why the 30amp fuse didn't blow?

according to AAW a direct short will blow the fuse. But if I had say right at 30 amp continuous load through the fuse it would get hot, but not blow the fuse. If I had wired that relay properly it would have never happened. I mistook the orange fan wire as continuous 12 volts where it's really a trigger only, so I had the entire fan(s) load going through the fuse all the time. With the relay wired correctly you'd only have 3-5 amps through that fuse.

Just goes to show that you do not want to wire up big fans, fuel pumps, headlights, etc. without a relay. I knew that of course, but by a simple mistake eliminated the entire advantage of the relay and the system was loaded like the relay didn't exist.

Jody

I would be asking more questions of the manufacturer. The fuse should blow long before the fire starts. Even if you are operating on the upper limit of the circuit rating, you should have no hot spots. Maybe you have bad connections in the fuseholder(s), and I would be checking the temperature of the others.

I would be asking more questions of the manufacturer. The fuse should blow long before the fire starts. Even if you are operating on the upper limit of the circuit rating, you should have no hot spots. Maybe you have bad connections in the fuseholder(s), and I would be checking the temperature of the others.

good points, and I initially thought it was loose terminals or similar in the fuse block. I have a new fuse block/dash harness coming, and when wired properly there will not be anywhere near 30 amps going through the circuit (less than 5 amps according to AAW), so I shouldn't have any more issues. I did order this today though, to be better prepared in the future:

http://www.lateral-g.net/g69/project/interior/safecraft_0004.jpg

In his first post he says it's a 30 amp spade fuse. I think the problem is right there.... The spade fuse drawing it's designed load for a long period of time got hot and then blew. (first occurence) With no real repairs made it happened again, but because the fuse holder was compromised it got hotter , faster.

Jeff

In his first post he says it's a 30 amp spade fuse. I think the problem is right there.... The spade fuse drawing it's designed load for a long period of time got hot and then blew. (first occurence) With no real repairs made it happened again, but because the fuse holder was compromised it got hotter , faster.

Jeff

very possible. That's one of the reasons I decided to replace the entire box, wires, and terminals, as I imagine that the coating on the fuse terminals have been damaged, which will cause more heat.

Jody

is auto, look at neutral switch, mine was orginal auto, the new switch shorted out after 1 week and burnt the fuse link and was burning a line under the carpet before the link fell apart. all new parts.

Just a little tidbit of information, GM actually has a tsb out warning about fuses from harbor freight (I don't know if HF actually produces them or is just a main source for them) but basically the fuses are so poorly manufactured that they will actually flow like more than double the current though them and still not blow. Resulting in extremely melted things and fires.