Method 4.7.28 is a mechanical life test (endurance at reduced load) for military relays. With rated coil voltage, the relay is cycled at 25 percent of rated resistive load for four times the specified minimum operating cycles for relays under 25 amperes contact rating (resistive), and two times the minimum operating cycles for relays of 25 amperes and over.
The cycling rate is that specified for resistive loads. Each relay circuit (normally open and normally closed contacts of all poles) is monitored during the test.
This test evaluates the long-term mechanical endurance and electrical contact reliability of the relay when operated at reduced loads, simulating typical operational duty cycles in military applications.