Why are the wires of thyristors always twisted in pairs?
Why are the wires of thyristors always twisted in pairs?


For the same reason that any twisted-pair cable is used: to reduce interference.

Thyristors such as that you have photographed are used in high-current circuits. The thyristor gates are relatively sensitive and an untwisted pair of wires running off to the control circuit will create a loop which will be susceptible to picking up induced currents which may trigger the thyristor.

By twisting the pairs a series of small loops are made and each one is in opposite orientation to the one before it. The result is that the induced interference is, to a very significant extent, cancelled out.

It appears that the device in your photo has four terminals: the stud and the heavy red lead for the high current circuit and the twisted pair for the control circuit. The reds are connected internally to eliminate problems trying to attach the control wire to the bolt on the large ring terminal.