located in an old building where large electric motors for locomotives where once rebuilt it has 6 large 48- volt 5 hp roof exhaust fans which help pull fumes and cool the plant when workers are busy welding .
One day when a worker went to start the fans as the temps started to rise outside there was a large buzz an tremendous explosion and then a flash of fire and molten metal luckily the blast did not hit him and he did not get hurt but all 3 motor controls on one side of the plant had exploded.
So what happened ?
After examining everything and climbing on the roof and looking at the fans I had the answer and it was disturbing as seen in image below
The entire system was improperly designed and there was a lack of fused disconnects which this job requires becuse a short circuit produces enough energy the breaker itself can not handle it. which over took it and allowed for an uncontrolled short circuit to roll all thru the circuitry
 |
| Totally arced over and destroyed controller |
 |
| no fused disconnect above controllers |
This is exactly what happened when in an attempt to put a safety disconnect on each fan to make it safe to work on it while on the roof they used a small bat handled disconnect switch which was in fact designed for 480 volts but they did not insulate the terminals and they put it in to small of a junction box which with vibration allowed the switch to arc over and it was completely destroyed and wiring charcoal-ed
 | ||
| Arced over safety switch |
The short then proceeded down the conduit to the controller and thru the controllers which tried to handle the short but could not and exploded. which finally broke the uncontrolled short. the breaker never tripped.
Had the fused disconnects been in place the damage would have been limited to the switch area on the roof and no where else and the large explosion and arc flash prevented.
Needless to say I had to replace all the controllers and switches much of the wiring and I installed a proper fused disconnect. to prevent future issues.
So you have to be asking yourself why was this install allowed in first place where was the inspections permits etc. in fact there was none .
Most industrial wiring is never inspected in Pennsylvania unless a company's insurance carrier mandates it most local code people want nothing to do with industrial facility they leave it to OSHA and insurance carriers to police it. In Fact most industrial electricians have not been properly school trained and certified either. Unlike my father and myself which had outside schooling most industrial electricians are OTJ on the job trained and if person training them is not properly trained then you have the type of problem you see here .
.