The Helios TSSW 1.5 is a built-in transformer designed for installation in a fuse board. Supplied without a housing, it features a base ring and terminal strip for easy connection. The unit provides five selectable voltage levels — 0, 80, 130, 170, and 230 volts — enabling precise control of fan speed in ventilation systems. Its compact and open design makes it suitable for integration into electrical panels where space and accessibility are essential.