MIL-DTL-2212K(SH)
3.15.1 Electronic overload relays. Electronic overload relays shall be tested in conjunction with the maximum
size contactor for which the electronic overload relay is designed to operate. When an electronic overload has the
capability to operate more than one contactor, each output of the relay must be tested. An electronic overload relay
shall have failed the endurance test if at any point during the test, it fails to energize or de-energize the contactor or
fail to perform any of the functions listed in 3.16.5.1.
3.16 Detail requirements.
3.16.1 Interlocks. Multi-speed and reversing controllers shall use electrical and mechanical interlocks to
prevent attempted operation in more than one mode.
3.16.2 Emergency run (see 6.8.29). When specified (see 6.2), magnetic controllers shall be provided with a
means of defeating the overload relay for emergency running. This feature may be combined with the overload
relay reset, or obtained with a separate push-button. Manual operation of the emergency run switch shall be
required for the duration of the emergency. Emergency run shall not be combined with the start push-button.
Actuation of the emergency run device and the start device shall be required to initiate emergency run. The control
circuit may allow releasing the start device after the motor has started.
3.16.3 Local transfer. When specified (see 6.2), controllers that are intended for use with remote switches shall
have a local and remote selector switch. This local and remote selector switch will disconnect the remote control
(see 6.8.16) wiring and allow local control (see 6.8.15). This switch shall prevent a damaged remote switch or
defective wiring from disabling the controller. Generally, a local and remote selector switch is required only for
vital functions such as steering and fire pump control.
3.16.4 Contactors and relays. Coils shall be encapsulated as specified in MIL-E-917. Coil leads shall
terminate at screw terminals. Contactor coils shall be readily replaceable. Contacts shall be of simple and rugged
construction. Contactor contacts shall be easily replaceable. Contacts, other than sliding contacts, used in control
circuits, shall not be plated, except with silver. Electrodeposited gold is permitted on control circuit contacts where
arc voltages and currents are not exceeded. Springs shall be constructed to ensure the proper functioning of the
relays and contactors. Springs shall not be stressed beyond their fatigue limits (see 6.8.41). The design shall be
such that springs are not depended upon to carry current. All bolts, nuts, and screws used for mechanical
connections shall be secured by split ring (helical spring) or external tooth lockwashers, locknuts, or double nuts.
All electrical connections utilizing hex nut fasteners shall employ split ring lockwashers to maintain contact pressure
and prevent loosening during vibration, shock, and thermal cycling. When the terminal mounting and wire
connection is common, a captive fastener shall be used to prevent the terminal capscrew and screw from rotating
when attaching or removing the wire lug. The contact assembly, as well as other current carrying parts of time delay
relays, may be plated with electrodeposited gold for corrosion resistance (see 6.8.70) purposes. Mating armature
faces shall not be plated, painted, or coated in any manner that will interfere with correct electrical operation.
3.16.4.1 Relays. Relays shall conform to this specification except that control relays may be in accordance
with MIL-R-19523, endurance Class A or B, shock Class I or II. MIL-R-19523 relays shall meet the applicable
requirements of this specification.
3.16.4.2 Network communications. Remote configuration capability shall not be permitted by design. All
configuration shall be performed via a local port that is not connected during normal operation.
3.16.4.3 Time delay relays. Time delay relays shall be electromechanical, solid-state with electromechanical
relay output, or solid-state with solid-state output. Setpoint repeatability (see 6.8.66) at constant operating
conditions shall be ±15 percent for electromechanical types, ±2 percent for solid-state knob adjustable and fixed RC
types, and ±0.2 percent for solid-state discrete switch and fixed digital circuitry types. The reset time shall be
75 milliseconds maximum. Time delay relays shall meet the endurance requirements of 3.15.
3.16.5 Overload protection. General purpose overload relays shall be used to protect continuous duty,
intermittent duty (see 6.8.27), and varying duty (see 6.8.28) constant speed or multi-speed AC motors constructed in
accordance with MIL-M-17059 or MIL-DTL-17060. Overload relays shall have tripping characteristics falling
within the acceptable band shown on figure 1. When tripped at 150 percent of rated current in an ambient
temperature of 68 °F to 86 °F (20 °C to 30 °C), overload relays shall be re-settable within 2 minutes after tripping.
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