Vacuum is the ideal dielectric for high voltage relay switching. It has extremely high voltage breakdown characteristics, a fast recovery rate and it provides an absolutely inert and non-reactive environment for switching contacts.

The absence of contaminating gases and vapors in vacuum relays means that contact surfaces remain brilliantly clean and contact resistance stays low and constant throughout the life of the relay.

The vacuum level in vacuum relays is typically better than 10-7 Torr, and improves through use as a result of the gettering action of small amounts of contact metal vaporized during arc interruption. Vaporized metal which supports the arc condenses almost instantly in a vacuum. This results in extremely high recovery rates of the vacuum dielectric, as great as 10 kV per microsecond. Corona effects do not exist in a vacuum environment because the mean free path of molecules is too great to permit collision ionization processes to cascade.

The high dielectric strength of the vacuum permits close contact spacing, on the order of 1000 volts per mil. The small movement required to operate a vacuum relay permits the use of small, low mass actuators allowing high operating speeds. Use of refractory metal contacts provides exceptional interrupting ability and assures long contact life.

Complete absence of exposed arcs makes the vacuum relay especially suitable for use in corrosive or explosive atmospheres. Changes in barometric pressure, temperature or humidity have no effect on the sealed contacts, permitting trouble free use in almost any environment.