A mechanical override device which is suitable for an undervoltage coil of a switching unit, is comprised of a first portion suitable for urging a plunger of the undervoltage coil in a first position which is taken by the plunger when the undervoltage coil is energized, and a second portion suitable for receiving an external movement command for imposing an operating movement to the first portion. The assembly includes a base assembly which includes a female pin contact holder, a base housing adjacent the female pin contact holder, and having at least one guide post, and a stem. This constitution makes it possible to provide a device structure which can be produced by an inexpensive production process, uses a composite material with an excellent thermoelectric conversion characteristic and can solve the characteristic problem of the composite material.