When an electrical system short-circuits, instead of current flowing from the power source
through a service (like a ridio, or oven) and back to the power source, it can take a "short ct" and avoid the resistance of the service. It's a bit like a hose in the garden, with your thumb over the end providing a resistance to the flow, take away your thumb (the resistance) and the water can shoot out of the hose. Electricity does the same, take away the resistance, and electricity can shoot along the wire. Now electricity moving along a wire creates heat, and the wire can only handle the amount of heat due to normal operations - given a short circuit, the wire will quickly overheat, and eventually cause a fire.
Circuit breakers are designed designed with bimetallic strips, which bend under heat, popping open the circuit before this heat damages either wiring or connectors. A specification might be for a breaker to trip under a massive short jolt (e.g. 10 times the rated load of the circuit-breaker for between .5 to 1.4 seconds) or a longer, less intense overload (e.g. twice the rated amperage for 3-130 seconds, depending on the type of circuit breaker). If the designed overload conditions are not exceeded, the circuit breaker will not trip. Some breakers are temperature sensitive and will trip earlier when warm than cold.
The very tolerances that must be built into a circuit breaker to prevent nuisance tripping also mean that when it does trip, it has a fairly major problem with the circuit, which is now heated up from that problem. Reset the breaker, and the wire, with it's insulation may catch fire before the extra energy can re-trip the breaker. Some glitches may not trip the breaker at all. Ticking faults and arc-tracking are examples. Ticking faults occur when tiny bolts of electricity intermittently arc from exposed wire conductor. On wires covered with aromatic polyimide wrap, installed in many aircraft built since 1970, this can burn the thin insulation, converting it into carbon, which is an excellent conductor – a nasty case of the insulator turning into the conductor! This can in turn lead to very short bursts (micro-seconds) of violent arcing where localized temperatures can reach extremely hot temperatures (well in excess of 1,000°C) capable of igniting nearby flammable material. Nevertheless, short, violent bursts of arc tracking will not necessarily trip breakers, which are comparatively slow-acting devices.
It is wise to think twice before resetting any circuit breaker in flight. It is telling you something is wrong – that there has been a serious electrical event. This danger signal must be interpreted with extreme caution. The old rule of thumb to automatically allow one reset is not prudent. Safety-conscious airlines are now telling their crews not to reset any breakers unless they are essential to safety and then to do so only once.
>paraphrased from
this article
You can have a look at
these circuit breaker rest fires from the UK Air Accident Investigations Board