Electricity experts, step inside

Recently I had a radiator fan motor fail (POS only lasted, literally, 299k miles). Meanwhile, instead of blowing the 30A fuse (blade type, shown below), there was what I assume was arcing going on between the fuse's blades and the female connectors in the fuse block; the arcing melted the plastic fuse body and part of the fuse block, but, yeah, the fuse itself never blew.

So, um, WTF. Is there such a thing as a bad fuse? The car is 27 years old -- maybe the fuses should be periodically pulled and cleaned up? I pulled a bunch of the others; they didn't seem corroded, but??

was the fuse (30A) over sized for the circuit?

30A is correct, per the manufacturer.

Yes there is such a thing as defective/dirty fuses. Clean the socket and replace the fuse.

If you don't have a good, clean connection, the high electrical resistance of the connection will turn into increasing heat with increased current. This can happen at ANY connection, or even damaged wires...too little metal for current to transfer through results in heat, then damages stuff...the exact same principle the fuse relies on, except the fuse fails in a more controlled manner.

Bryce

I have seen sockets that aren't rated for that kind of constant current flow from the factory... It isn't uncommon..

There also has been a rash of cheap blade type fuses out that don't work properly...

You can produce a great deal of heat with 25 amps of current flow, particularly once the connector starts to loosen up or corrode a bit. I haven't had to do one for a while, but it was pretty common to have to add in a remote fuse holder in 700 Volvos for the heater fan after the fuseblock melted.

Yeah, what they said. And if the extra resistance is on the feed side of the fuse (the arcing and melting) the excess amperage (current flow) never crosses the fuse, thus it won't blow.

I've got big block fuses with blade connectors as main battery fuses on my 'rolla, all are welded in place, and they're in a box so the connectors should be clean (not that I could ever see them without using a dremel.)

DrBoost wrote: Yeah, what they said. And if the extra resistance is on the feed side of the fuse (the arcing and melting) the excess amperage (current flow) never crosses the fuse, thus it won't blow.

This would only be the case if it was shorting to ground. In the case of a downstream component pulling the load, the same current pulled through the fan motor will be pulled through the fuse connections.

Bryce

You're right. Current flow is the same everywhere in the circuit, only if that connector was shorted would that happen.
Sometimes I forget electrical 101.