Employees were lowering the bottom half of a distribution box into an excavation when the shackles became caught on the notch outs. The load was re-rigged with wire to allow the box to be completely set into place. One of the shackles was stuck and the injured employee was trying to get it to break free. The wire broke before the shackle could be released, allowing the load to drop on the employee's foot and partially amputate the employee's left big toe.