The switch is enclosed in a casing (1) which contains also a trigger electrode (5), releasing a discharge between the cathode (3) and anode (2), on application of a suitable voltage. The cathode is of evaporable metal, which is solid at room temp. Pref. the trigger electrode is located adjacent to the gap (d) between the anode and cathode. Typically the trigger electrode is cylindrical surrounding the gap such that a potential difference is maintained between the cathode and anode in operation. On application of the trigger voltage, a discharge takes place between the anode and cathode.
