I have seen a few Arc Faults - none which would qualify as "Large", but were "Large enough for me!"
Also saw the results of a large and bolted fault, and a few failed devices.
The Arc Faults were mostly on 480 VAC equipment, however I had witnessed two separate events on lower voltages - one was at 208 volts, the other was at 120 volts.
First the 480 Volt mishaps:
2 from mis-rated fusible disconnect switches, failing during a fault on the load side.
The equipment fed from the switches had large Induction Motors, driving very heavy dynamic inertia loads.
Someone dropped a steel beam across the load side conduits to these machines, resulting in a 3PH bolted fault.
The fuses in the switches opened first - but the switches were rated for 240 volts, and were very undersized for the conditions! (not only rated for 240V and using fuses rated for 240V, but general purpose types too!)
Currents simply Arc'd over the opened 240V fuses, which must have evolved into L-L-L Arc faulting within the first few minutes.
Soon afterwards, the switch enclosure's front covers were blown open, and finally the branch circuit's OCPD tripped (likely from a solid ground or line to line fault).
We were quite a distance away, but it really made an impact! Loud and scarry!
The other one was in a section of Switchgear, which had failing terminations across the bus kit.
That one turned into an L-L-L Arc Fault first, then branched over with L-G Arc Faults - of which, activated the GFPE Trip on the Main Service Disconnect.
We were sent to service an "intermittant loss of power" problem, and had this take place while we were opening the suspected gear section (another reason to always wear PPE!!!).
As to the lower voltage arc faults, saw one on a 3PH. 208 VAC Heat Pump Branch Circuit, which was run across the roof, and tripped over by nearly every person ever walking by it! (the EMT resembled the symbol for a Resistor!)
Since the EMT was not bonded with an EGC, any L-G fault would leave the conduit hot - and resulted in a "kind of" corner grounded system (not a real one, but in the same way an ungrounded system will somewhat become corner grounded if one line gets faulted to metallic equipment).
We were repairing the HVAC Branch Circuitry - and the roof equipment was also being upgraded by others at the same time.
Some poor guy tripped over an EMT run for its last time.
That thing went nuts! Fittings were being blasted apart everywhere; Arcs were forming between conduit ends - and as they moved further apart, the Arcs turned into large Plasma flames.
Previous EC must have been from Kaos, Inc.
Lastly, saw a Photocell turn into a red flare from an internal Arc Fault. This was a 120 VAC circuit.
That was really bizzare!
As to component failure, I have seen a few Breakers which ended up having the contacts fried closed.
Saw one frame which may have been damaged from an explosive fault condition.
Saw a size 2 Motor Starter explode from a combination of mistaken circuitry and a bolted L-L-L fault condition.
Luckilly, I was a distance away when the guy whom wired it went for a smoke test.
Will never forget that one!
The worst accident ever (so far), was due to some clown(s) attempting to steal the Main Service Disconnect (Circuit Breaker) from our switchgear's service sections.
They got away with the first one, but when they returned a few days later to get another one, the PoCo enegized the Transformers (which were not energized during the prior theft).
This particular gear section was no more than 50 linear conductor feet from the Transformer.
Transformer was a 500 KVA, 5.0% Z pad mount, and the Gear was fed with Paralleled 750 MCM al. It was a 1200 amp section & breaker, so there must have been 3 sets of 750's feeding to the UGPS's lug landings.
The thief created a bolted L-L fault, which even though it's only 87% of the available L-L-L value, still had one hell of a punch!
There was splattered aluminum all over the place - similar to a textured wall!
Huge blast / flame marks scorching the enclosures and the "proposed ill-gotten booty" 1200 Amp breaker - rendering it useless.
Bus bars feeding the breaker were completely destroyed.
Oh, and the bandit(s) left their tools when they fled.
edited to fix spelling blunders!
[This message has been edited by Scott35 (edited 08-30-2006).]