Brief Description of Incident:
A crew was lifting an underground switch off of their trailer with a digger derrick using 5/8″ bolts screwed into the switch case. While lifting the switch, the hoist locked out with the switch about 1″ above the trailer. The switch dropped to the trailer when one bolt bent and the other flew out of the switch case. The switch and the trailer were not damaged.
5/8″ galvanized bolts were not the proper bolts for lifting and failure of the hoist to lift was an indication load was too heavy. A review committee determined that tap and die should have been used to clean the bolt threads and lifting attachments are being ordered for similar loads.