Cause of Blown Fuse?

A short circuit is my WAG. This could be caused by frayed wire insulation. You might even be having electronics (capacitor) breaking down but that will be difficult to trouble shoot.

If you can see inside the failed fuse element area (a glass fuse) look to see if the whole fuse element vaporized. This will happen when a large overcurrent condition happened like a wiring short circuit causing the fuse to quickly open the circuit. If instead the fuse element appears to be intact or only a small break in the element exists then either a small but repeated overcurrent condition happened over time making the element brittle. In this latter case one only has to replace the fuse. A technician or electrical engineer with additional testing equipment may be able to safely modify the circuitry to prevent future "soft" fuse failures but simple replacement will still likely be the most cost effective solution.

Simply replacing a fuse that blows often is bad and extremely dangerous advice! If a fuse blows there is a fault which could if left running could potentially cause a fire or electrocution injury to operating personnel. You don't know if the fault is getting progressively worse. Get a qualified person to diagnose and fix the fault.

The first thing to do is to check that this is the proper fuse for that location...so you'll need a wiring diagram for that model number of CAT...Then get a few replacement fuses, and clean the fuse holder properly and I would add some conductive grease to both the fuse holder and the fuse contact surfaces...and replace the fuse...If it blows again immediately, then you know you have a short...so now you have to trace it out to check if possibly a component has failed, or the insulation on a wire has failed and the wire is touching to ground....

Make sure you follow recommended maintenance procedures...

http://csdieselgenerators.com/Images/Generators/2114/CAT-3412C-_Generator-Set-_Manual.pdf

Simple. There was a fault. The current passing through it at the fault event was more than it was designed, developed, type-tested and warranted to withstand. It did its job in disconnecting it. Somewhere else, there will be a mark where something went BLAT! All that is needed is to locate it. That spot cannot be seen from here.

That's not necessarily true, if there is a bad connection in the fuse holder it can heat up causing the fuse element to melt...

Correct. Or it could be a simple matter of trying to connect and run too many devices at the same time, or a single device that requires more startup current than the generator can safely provide.

That would indicate a design problem.

True, but we've all seen bad designs in use before.

Possibly. In a Google search, I failed to find a CAT generator with the model #700; so I have no idea of the size of this generator. If it is a generator with an output of 700 VA, this fuse could be in the output circuit. If it is a generator with an output of 700 KVA, then obviously the fuse would have to be feeding the control circuit.

We obviously need more info re: the specific model.

You might have more luck if you revealed the actual model number of the generator, this could be perhaps a 700kW or 700kVa or 700W generator, your 10A fuse might be control power, not likely to be excitation or stator leads. It’s likely that some unknown component failed, or that a wire insulation failed at a chafe point, so the control circuit is short circuited.

http://777parts.net/caterpillar/3304B/m471/SEBP34470178.html

There is only one way to find out why the fuse blew and that is to fault find on the circuit with the generator not running and ascertain where the fuse is in the electrical circuit.

Before any reasonable hypothesis as to why the fuse blew it is necessary to have more information on the generator rating and the actual circuit the fuse is to protect? Is it on the diesel motor protection and connected to 24V to feed the oil, water, fuel pump, fuel shutoff Mobray switch, or whatever, usually a glass fuse or a normal automotive type.

If in the DC excitation circuit, does it feed the exciter winding or the AVR, auto voltage regulator or in the AC to DC rectifier. The fuses used in this section are often HRC fuses.

More information is needed before anyone can even hazard a guess as to the cause of the open circuit adjacent fuse ends

on the older style generators (15yrs old) the cap is the first thing that goes wrong on portable generators. on the newer generators there is a voltage regulator assembly. the second would be to check the carbon contacts.

i'm not sure this would cause a direct short, but repair a unit, this is where you would look to before all other. a direct short should be on the other side of the fuse. i would first put an ohm meter (or a continuity tester) and measure between the wire and the frame (not painted) you will probably find that there is a direct contact.

at this point it is just finding the component or wire that is the culprit.

Thanks to you all, I've gotten the fault, it's a faulty wire bridging each other

Good! Now comes a tricky question many overlook, why did the insulation breakdown? From my experience this happens most often because the the wiring bundle was not properly strain relieved and/or secured to another support structure. Having a bundle of wires self supporting themselves in a high vibration environment like a generator will cause the insulation to be eventually chaffed away and shorting out the conductors.

BLAT indeed.

I've gotten the fault, it was a wire insulation failure. Thanks

Every day is a leaning day.

BLAT indeed.