A 1900 LB PLC CABINET HAD TO BE BROUGHT INSIDE & INSTALLED ON A 3"" HIGH PAD. THE CABINET WAS IN AND BEING MANEUVEREED ONTO THE PAD. EE HAD A PRY BAR TO LEVEL 1 CORNER UP AT A TIME. THE CABINET SHIFTED AND CAUSED THE LEVER TO MAKE A QUICK DOWNWARD MOTION THAT CAUSED EE TO STRAIN A MUSCLE IN HIS BACK.