MIL-STD-202-312 Notice 1 - Validation:2020

This test is conducted for the purpose of determining the electrical contact reliability of such items as electromechanical relays, switches, etc., under intermediate current (formerly known as \"minimum current\") switching conditions under which the contacts operate. An intermediate current switching circuit is one in which there is insufficient voltage and stored energy to cause contact arcing during opening or closing of mating contacts, but which have sufficient energy to cause melting of the contact material. Normal arcing of contacts at rated load levels often act to burn off any oxide or other film on the contacts or provide localized melting at the point of contact, so that contact resistance does not rise drastically. Without this arcing of the contacts, oxides and other contaminant films can build up on contacts in component parts which have not been sealed adequately or which have contaminating materials and vapors trapped within the enclosure due to improper manufacturing techniques. Such contacts will develop unacceptably high contact resistance under intermediate current loads, unless the contact force and wipe are sufficiently heavy to overcome any effect of contamination. Intermediate current switching is the range in which a large percentage of loads occur. Therefore, it is extremely important that an intermediate current switching test be imposed on all electromechanical relays and switches, which are to be used in this range. Relays and switches, which pass both low level and full rated load tests, frequently fail when used in the intermediate current switching range.