Sunvic 602 hot wire vacuum switch

This switch measures 118x25mm overall and has 4 leads.

This device is a switch connected to a bi-metallic strip which is heated by a coil, all encased in an evacuated envelope.

The label on this device reads "Sunvic hot-wire vacuum switch
type 602
style 136787

Control current must not exceed 30mA. Control circuit resistance 1800 ohms approx. Unless one lead is common to the control circuit, the series resistance must be in 2 parts, 1 in each lead and neither part must be less that 500 ohms. Patent No. 354020 & others.

Underneath is written 14.0V / 3.5mA 27/6/73