Switches covered by this specification are intended for use in ac and dc applications. Switches are for single phase use only and are not to be used to transfer from phase-to-phase, unless otherwise specified. Contacts may be paralleled for reasons of redundancy or to reduce the total contact resistance, but they must not be paralleled for the purpose of switching currents greater than the published ratings of a single contact. Another switch with suitable contact rating must be used. These switches are military unique due to the fact that these devices must be able to operate satisfactorily in military systems under the following demanding conditions: −65°C to +350°C operating temperature range, 100 Gs of shock, and 30 Gs of sinusoidal vibration. In addition these military requirements are verified under a qualification system. Commercial components are not designed to withstand these military environmental conditions.

Switches have electrical load ratings specified by the specification sheet. The electrical load ratings normally reflect the maximum electrical load that the switch can properly control for a specified minimum cycles of operation. In selecting a switch for a particular application electrical load, the electrical ratings of the switch should be compatible with the application load. For application loads with sufficient voltage and current to cause arcing (approximately 8 volts and 0.5 ampere), any switch with higher electrical ratings will properly control the application load. For application loads with insufficient voltage to cause arcing but with sufficient voltage to melt the contact material, (approximately .5 to 8 volts), a switch with logic load ratings should be selected. For application loads with lower voltages (below .5 volt), a switch with low level ratings should be selected. The load handling capability of an unsealed basic sensitive switch may be affected when used in sealed switch assemblies. Each contact rating and temperature characteristic must be evaluated on the sealed switch assembly.

Contact bounce and transfer time of most sensitive, snap action basic switches is of concern when used to control devices having very fast response time. In the case of a double throw, break-before-make, snap action switch, there is no circuit through either contact during the transfer (snap over) time. Thus, there will be a definite interval between the time one circuit opens and the other closes. Associated with circuit closure is contact bounce. When the moving contact strikes the stationary contact, the kinetic energy is converted to heat and potential energy in the form of deformation of the contacts. As a result of elastic deformation, the moving contact rebounds from the stationary contact, the contact pair being reclosed by the contact force. This can occur one or more times until bouncing ceases and the contact system reaches static equilibrium.

In general, the combined transfer time and bounce time will usually not exceed five milliseconds and cause no problems on slow responding devices. On fast responding electronic logic circuits, each contact bounce may be erroneously interpreted by the circuit as a separate signal causing a false output. To compensate for the contact bounce of the switch, a ten millisecond buffering circuit is usually adequate to prevent false outputs of the logic circuit.

The environmental conditions in which a switch must control a logic load level or low level electrical load may directly affect its performance in the application. Under these electrical load conditions, there is no arc present to remove contamination from the contact interfaces which prevent proper contact closure. The probability of proper contact closure under nonarcing conditions is inversely proportional to the contamination in the environment. The detrimental effects of environmental contamination can be significantly reduced by one or more of the following:

a. Enclosure: By enclosing the contacts in a sealed enclosure, the contacts are protected from the environment.

b. Contact material: The use of gold at the contact interface will prevent the formation of sulfides and oxides.

c. Contact configuration: There are two basic contact concepts specifically suited for nonarcing electrical loads:

(1) Multiple-point contact designs to provide redundancy such as bifurcated contacts.

(2) Point-to-plane or point-to-point contact designs such as wedge-shaped contacts, crossed-cylinder contacts, or crossed-prism contacts.

The intermediate current test is used to test the low energy capability of a power switch (see 4.7.32).

Where a switch is intended to "make" and "break" a low level circuit, the low level test requirement should be used (see 4.7.33) and, if possible, a switch with sealed contact areas should be utilized.

Boots, when used to provide a panel seal, should be in accordance with MIL-B-5423, "Boots, Dust and Water Seal (For Toggle and Push-Button Switches, Circuit Breakers, and Rotary-Actuated Parts), General Specification for".

The finishing of metallic areas to be placed in intimate contact by assembly presents a special problem, since intermetallic contact of dissimilar metals results in electrolytic couples which promote corrosion through galvanic action. To provide the required corrosion protection, intermetallic couples should be restricted to those permitted by MIL-STD-889.

Switches using phenolic plastics are not to be used for submarine applications.

Government contracts commonly specify that military standard components be used and that MIL-STD-1472, Human Engineering Design Criteria For Military Systems, Equipment and Facilities, applies. Due to performance and environmental requirements, or other factors, military specification switches frequently do not meet the requirements of MIL-STD-1472. To provide the desired operability, it is suggested that equipment designers select the military specification switches which can most closely conform to the human interface requirements of MIL-STD-1472 without sacrificing reliability.