In this video, a plant maintenance technician attempted to air-run a chiller for vibration analysis. There must have been a short to ground on the load side of the start contactor at the transistion resistor bank, behind a bundle of wires not visible if you are not looking for it. Needless to say, there was a short to ground and a pretty decent electrical explosion that looked like a fragmentation granade detonated in the starter panel.
 
Access this 37-second video by clicking on the link below.