What Causes Arc Faults, How Are They Different from Short Circuits, and How Do AFDDs Work?

what cause an arc fault to occur? and what is the difference between it and short circuit fault? and does the afdd interrupt the arc or just predict it?

Wikipedia has a good definition of arc fault.https://en.wikipedia.org/wiki/Arc_fault
In a short circuit, the fault current flows through a conductor, in arc fault, it flows though the air.

I would hope that an arc fault detection device (afdd) would interrupt the arc but it might just send a signal to a circuit breaker.

FarahWe often test our products for isolation up to a particular voltage. If the unit fails, and there is an arc, we find that the isolation is compromised from there on. In other words if it passed at 1.5KV and failed at 2KV, it will not pass a second time at 1.5KV or even 1KV. The circuit isolation is compromised and the unit under test is figuratively, if not literally, toast.. 
It is rare for a short circuit to damage the circuit in this way (if the fuse/circuit breaker manages to protect the circuit).

The difference between an arc fault and a short circuit:An ARC fault occurs when the air or insulation between two conductors becomes ionised (due to a high voltage between the conductors).  Ionised air is a conductor and a current - usually excessive - will flow between the conductors,  As Aubrey says, in the case of physical insulation the effect may be permanent or degrade the insulation.A SHORT CIRCUIT occurs when a (usually) metallic connection is made between two conductors.  Again excessive current usually results and permanent damage may occur if insulation is melted, etc.  Water or other substances may also cause partial short circuits which have similar effects.You can get a short circuit on a 3.3V power line that would never arc.

A bit more...An AFDD does not predict an arc but senses it and interrupts the circuit to extinguish the arc (as arcs are a prime cause of fires).  An Arc may not appear like a short circuit and may not have enough current to trip a circuit breaker, depending upon the other impedances in the circuit.There's a good article on AFDDs from a respected manufacturer here.