Block and Tackle

transformer is dropped or severely jolted. The lifting equipment, including the slings, should be carefully inspected before the operation is started. The linemen and groundmen should stay clear, while the transformer is raised into position. Appropriate personal protective equipment must be worn at all times. Block and Tackle Block and tackle are used for applying tension to line conductors when sagging in, for applying tension to guy wires when hoisting transformers, and for other general-purpose hoisting. The use of block and tackle has two advantages: (1) the user can stand on the ground and pull downward while hoisting or lifting a load and (2) the manual force applied need only be a fractional part of the load lifted. To find the pull required to lift a given weight with a block and tackle, divide the weight by the number of ropes running from the movable block. The lead line, or haul line, is not to be counted. Some friction loss always occurs around the sheaves. This can be estimated at 10 percent per sheave and added to the load to be lifted. The load that may be lifted is therefore the mechanical advantage times the safe load on the rope. Safe lifting load requirements for rope can be found in chapter 3. The block and tackle, as shown in figure 4-41, is called a four part block and tackle because it has four times the mechanical advantage for lifting an object. Again this is Figure 4-40.—Pole gin. determined by the number of ropes (four), not counting the hauling line running from the movable block. Lifting Straps and Slings Whether lifting with the block and tackle or a winch, you will also need lifting straps or slings to se- cure the equipment being lifted to the lifting apparatus. Figure 4-41.—Block and tackle. 4-21