MIL-PRF-17773C(SH)
3.4.2.3.9 Line circuit time delay (LCTD). When specified by configuration type (see 1.2.3), ABTs shall be
provided with a time delay between the opening of the main line contacts and the closing of the other set of main
line contacts (OFF position) as shown in Table IV. The CCTD and the LCTD may be incorporated into a single
device, provided that the total time delay does not exceed 4 seconds. LCTD shall be suspended after the voltage
level falls below 20 percent.
TABLE IV. Line circuit time delays.
Time Delay
Current Rating of
Switching Mechanism
(seconds)
50 A or less
1 to 3.5
Over 50 A
2.5 to 3.5
3.4.2.3.10 Transfer stabilization time. When specified by configuration type (see 1.2.3), re-transfer shall be
inhibited for 100 to 150 milliseconds after transfer to allow for source stabilization.
3.4.2.3.11 Drop-out and pick-up frequency (60 Hz applications). Drop-out and pick-up frequency for
configuration types (see 1.2.3) shall be in accordance with Table V. Tighter tolerances may be specified (see 6.2).
TABLE V. Drop-out and pick-up frequencies.
Drop-out Frequency (Below rated
Pick-up Frequency (Below
Configuration Type (CT)
frequency, 60 Hz)
rated frequency, 60 Hz)
CT05
2-3 Hz
1-3 Hz
CT07
4-7 Hz
1-3 Hz
CT08
4-7 Hz
1-3 Hz
3.4.2.3.12 Full phase protection. Unless otherwise specified (see 6.2), full phase protection shall be in
accordance with configuration type (see 1.2.3). Full phase protection is monitoring all three phases.
3.4.2.3.13 In-phase monitoring control circuit. When specified by configuration type (see 1.2.3), ABTs with
in-phase monitoring shall complete transfer when the two sources are within 60 electrical degrees of each other.
3.4.2.3.14 Transfer inhibit on overload. When specified by configuration type (see 1.2.3), transfer shall be
inhibited if the load current supplied by the switch exceeds 125±5 percent of the switch ampere rating unless
otherwise specified (see 6.2).
3.4.3 Transfer test. The ABT shall include an automatic mode test. The test shall simulate a power source fault
to verify that the ABT transfers power to the other source.
3.4.4 Maintainability. The maintainability capability provided for the unit when combined in a target system
platform shall make it possible for the assigned maintenance personnel to perform necessary unit equipment repairs
at the organizational level within the mean time to repair (MTTR) criteria specified herein. The MTTR shall not
exceed 30 minutes. The maximum time to repair (Mmax) at the 95th percentile shall not exceed 60 minutes. Time to
repair shall be the sum of the time required for:
a.
Fault localization
b.
Fault isolation
c.
Disassembly
d.
Interchange/repair
e.
Reassembly
f.
Repair validation
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