MIL-DTL-2212K(SH)
i. The stop device of a controller shall be so connected that the controlled device will be de-energized and can
be started again only upon actuating the start device (see 6.8.78). A controller designed for low voltage release
(LVR) (see 6.8.44) shall have a maintaining type switch connected such that controller restart can be prevented.
j. When the circuit arrangement incorporates ten or more control or timing relays, a programmable logic
controller (PLC) (see 6.8.55) shall be considered.
3.8 Reduced voltage (see 6.8.62) controllers. Reduced voltage controllers shall provide closed circuit
transition.
3.9 Load isolation (see 6.8.39). Unless otherwise specified (see 6.2), opening of the line contactors shall isolate
all portions of the load from the line except control circuits and the incoming power terminals. A discharge circuit
shall be provided for shunt field winding DC controllers.
3.10 Remote device circuits. Control circuit leads from controllers to remote devices shall be protected against
damage from short circuits. Leads wired in series with current limiting (see 6.8.42) parts, such as coils and resistors
(see 6.8.73), which are located within the enclosure will be considered to be adequately protected. Leads not
protected by current limiting parts within the enclosure shall be fused. Unless otherwise specified (see 6.2), remote
indicating and monitoring circuits shall be independently fused so that a short circuit in these circuits will not
prevent the controller from performing its function. Fuse sizes shall be in accordance with MIL-E-917. When fuses
larger than 10-ampere capacity are required, 15- or 20-ampere fuses shall be used as appropriate.
3.11 Overload protection (see 6.8.56). Overload protection shall be provided for the motor during starting and
running conditions.
Resetting (see 6.8.67), if not automatic (see 6.8.4), shall be accomplished by means external to the enclosure.
When two single-pole relays are used with three-phase motors, resetting of the two relays shall be accomplished by
a single button. Automatic reset (see 6.8.68) overload relays (see 6.8.65) shall not be used with controllers arranged
for LVR. When an overload protection system requires external power, the power source shall be the motor power
line or the motor control circuit. Overload protection shall not be provided in DC controllers for submarine service;
however, provision shall be made for wiring to an over-speed trip module, if required (see 6.2). If an electronic
overload can be used for both single- and three-phase operation, a means shall be provided such that the overload
will properly sense current imbalance in both configurations.
3.12 Ambient temperature ratings. The ambient temperature rating for the motor controllers shall be in
accordance with 3.12.1. The ambient temperature rating for the controller and associated switching devices shall be
3.12.1 Rating 122 °F (50 °C). The rating of controllers shall be based on an ambient temperature of 122 °F
(50 °C) for those installations where the maximum normal operating temperature of the surrounding atmosphere or
other cooling medium is 122 °F (50 °C) or less. Motor controllers constructed for use in a 122 °F (50 °C) ambient
temperature shall withstand exposure to an ambient temperature of 158 °F (70 °C) without damage.
3.12.2 Rating 149 °F (65 °C). The rating of the contactors and associated switching devices, including solid
state switching devices, installed inside controllers shall be based on a controller internal air temperature of 149 °F
(65 °C). Contactors and associated switching devices constructed for use in a 149 °F (65 °C) ambient temperature
shall withstand exposure to an ambient temperature of 185 °F (85 °C) without damage.
3.13 Wiring. Permanent internal wiring shall be copper wire or bus bar. The size, stranding, and insulation of
wire, and the dimensions, insulation, and spacing of bus bars shall be mechanically and electrically suited to the
application. Hook-up and lead wire shall be as specified in MIL-DTL-16878 or commercially similar UL listed
types as approved by NAVSEA. Polyvinylchloride (PVC) insulation shall not be used. Magnet wire shall conform
to NEMA MW 1000. Wires connecting to resistors or Class H coils, and wires otherwise exposed to heat shall have
a minimum temperature rating of 257 °F (125 °C). The minimum temperature rating for all other wires shall be
221 °F (105 °C). Wire size shall be chosen such that it is capable of carrying the expected full load current of all
connected components. AWG 14 and larger shall be used for all components that accept this size wire. Provided
ampacity requirements are met, AWG 16 may be used for connections to local switches and AWG 22 may be used
for connections to PLCs and solder connected devices as appropriate for device termination.
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