Electricity charged through the rig as one of the rescuers began administering CPR. But the second worker touched the still-electrified crane, sending a deadly surge through all three men, authorities said.
"He put his hand on his shoulder, and he steadied himself on the crane, and that's when they all got it," a local police chief told AP.
Horrified co-workers could only stand and watch until the live wire was shut off, said the general manager of the JDM Materials plant where the accident took place.
While they waited, the crane became so hot with live power that it caught fire.
The crane was left a smoking hulk. A 7,200-volt electrical line remained draped over its boom hours after the disaster in Telford, in suburban Philadelphia.
Witnesses said the crane was backing up when it ran into the wires. The three worked for a company that had been hired to demolish an old structure at the plant.