Criteria for choosing stringing blocks

Criteria for choosing stringing blocks are as follows.

a)    For best results during the stringing and sagging operations, the minimum diameter at the bottom of each conductor sheave groove (sometimes called root diameter) should be:

D_S =20D_C−10

Where D_s and D_c are in centimeters and Dc is the diameter of the conductor to be installed.

NOTE the above ratio may be exceeded as required by some countries, codes.

b)    The minimum depth of the sheave groove should be:

Dg = 1.25Dc

c)    The minimum groove radius at the bottom of the groove should be:

Rg =1.1D_C /2

The groove profile and the groove radius should be wide enough to allow passage of conductor swivels and woven wire grips without these riding high in the groove and imparting a shock load to the sheave. It is important also to consider the shape of the sheave groove if it is desired to make conductor compression joints in front of the tensioner and pass these through the stringing blocks. In this case a wide sheave groove should be considered.

d)    The sides of the groove should flare between 30° and 40° from the vertical to facilitate passage of swivels, conductor compression joints, conductor woven wire grips, etc.

e)    It is appropriate that the chassis of the unwinding pulley allows a top or side opening for easy removal of the drivers during the setting clips operation.

It is appropriate that the groove of the pulley peeling or location through which the driver is designed to allow passage without shaking a peeling rudder in the case of a beam, or tablet sleeves driver, swivels, pulling loops of cable, etc. It is appropriate that these objects do not come into contact with the frame of the pulley.