MIL-PRF-17773C(SH)
3.4.5 Front panel. The front panel shall provide the operator with the controls and indicators necessary to
monitor the status of the normal and alternate power sources. All ABT controls and indications shall be located on
the front of the unit.
3.4.5.1 Indicator lights. Indicator lights shall conform to MIL-DTL-3661, MIL-L-3661/38, MIL-L-3661/62,
MIL-L-3661/63, MIL-L-3661/64, MIL-L-3661/65, MIL-PRF-19500/519, MIL-PRF-19500/572, and MIL-PRF-
19500/708, as applicable. Indicator lights shall be furnished with lamps or LEDs. For position indication of circuit
breakers, blue indicator lights shall be used to show that the circuit breaker is closed. Other indicator lamps have
color caps as specified for the particular application. The color code shall be as follows:
a.
Red danger or emergency condition requiring immediate attention or corrective action.
b.
Green normal condition.
c.
White power available or power on.
d.
Blue closed, advisory.
e.
Clear (not etched) synchronized or ground detector lights.
f.
Yellow abnormal, but not requiring immediate attention.
3.4.5.2 Controls.
3.4.5.2.1 Indicator test feature. When specified (see 6.2), the ABT shall provide a feature for indicator testing.
3.4.5.2.2 Mode. ABTs shall be provided with a selector switch that controls manual or automatic ABT mode
of operation. (see 3.4.2.3.1)
3.4.5.2.3 Manual operator switch. The ABT shall provide a manual operator for the purpose of transferring
power sources in manual mode.
3.4.5.2.4 Transfer test switch. The ABT shall provide a transfer test switch for the purpose of initiating a
transfer test. The test switch shall be of the momentary spring return type.
3.4.5.2.5 MBT OFF position. MBTs shall have a definitive, sustained OFF position between the two
energized/closed positions.
3.4.6 Fusing of control circuits and indicator circuits. Switches shall have fused control circuits (see 6.4.6) and
indicator circuits as necessary to prevent damage in the event of operating component malfunction.
3.4.7 Manual operating controls. Manual operating controls shall be external to the enclosure and located in a
readily accessible position.
3.4.8 Manual operating handle or lever for automatic bus transfers. Protruding manual operating handles or
levers for automatic bus transfer switches may rotate when the transfer switch is on automatic operation. When on
manual operation, the operating handle shall indicate by mechanical position which source of supply is connected to
the load circuit. For automatic bus transfer switches which utilize an inherent double-throw transfer mechanism, a
white light shall be provided with an instruction plate to define the parameters for mechanical operation when only
one or both sources are not available.
3.4.9 Interlocks. Interlocks (see 6.4.11) shall be provided to prevent simultaneous operation of elements of the
switching mechanism which could result in improper operation or a short-circuit condition. The interlocking
mechanism shall be either electromechanical or mechanical. Electromechanical interlocks shall require power to
defeat. If simultaneous operation may be caused by only electrical means, the interlocking may be electrical only.
The interlocks shall prevent one set of switching elements from closing when the other set of switching elements are
not fully open so that two power supply lines are not simultaneously connected to the load or cause an arc between
the two supply lines.
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