C172 alternator issue

[navygm]

At work we have a C172 (forgot the exact year) its an old one, and has got an intermittent issue, that every some flights the alternator C/B popps out for no particular reason, checked if it was one of the lights, checked pitot heat, and also checked all wiring which seems to be good. Radios all work fine.
Battery is charging so even that is working.

anyone has some hints maybe? what could be the cause by any chance

[tpng conehead]

Have you done a load test on the C/B.

[Uplinker]

@ tpng conehead +1

And also measure the alternator current output. Your battery for example might be knackered and drawing max+ current from the alternator.

You say the wiring is OK, but are you quite sure that the insulation has not chafed (sp?) somewhere and is shorting to earth intermittently?

[stevef]

+ 1 for the wiring. Had exactly the same symptoms with a Cessna twin a couple of weeks ago. The prop-blast was occasionally blowing the field wire against the alternator and had eventually chafed. It was clear when the engine was shut down but the arcing was (just) visible on the case.
Have had faulty double Master/Alternator rocker switch causing the same symptoms as well. Loose terminals can be to blame too. Take your time and check all physical connections.

[Corrosion]

Is your plane old Continental six cylinder model, or newer Lycoming four??
Most propably it is wiring problem as mentioned above, if you have ALT and ALT fiels c/b:s separately which one pops?

Common point for wire chafing is just behind alt, and/or where they go thru front baffle. (Lycoming. Continental alt is installed to rear of the engine if it is old O-300) Bad clamping around eng compartment is very common as well, wire chafing to clamps because rubber cushionings worns away.
Sometimes wiring harness drooping just littlebit too close to exhaust risers...