De-energized tap-changers are used to adjust the voltage setting of oil transformers. Unlike on-load tap-changers, the adjustment of the desired winding tap must take place with the transformer de-energized.

Designed in accordance to the British Standard assembly, 085 and 086 series are manufactured with rotary setting of the drive equipment. The moving contact is specifically ring-shaped in order to allow self-centering. Adjustable shaft length and modular layout are combined to obtain a switch with maximum efficiency.