MIL-PRF-17773C(SH)
4.6.16 Endurance and overload. Bus transfer switches shall be tested for overload and endurance in accordance
with Table X. Switches shall be energized for a minimum of 1/6 of a second before and after transfer. Operation
cycles shall be initiated by the loss of power from either source. The ABT must be powered down between
operation cycles. Unless otherwise specified (see 6.2), Method II is applicable to AC ABTs without time delay and
not for switchboard service, and Method I is applicable to all other ABTs. These tests may be conducted on one set
of contacts. However, in no case shall the specified operating cycles cause damage to components from excessive
heating. ABTs shall fail the overload and endurance tests if they fail to perform their intended operating functions
during or after the tests without adjustment, calibration, or replacement of parts, excluding a one time replacement of
TABLE X. Endurance and overload test conditions.
Overload test conditions
Test
Test
Number of
ABT and MBT
Load power
voltage
current
cycles of
Time limit
factor
(percent
(percent
operations
rated)
rated)
AC (method I)
50
600
100
0.40-0.50
1 hour
AC (method II)
50
150
100
0.70-0.80
1 hour 40 minutes
DC
50
400
100
-
1 hour
Endurance test conditions
Test
Test
Minimum make
Number of
Load power
voltage
current
and break
cycles of
factor
(percent
(percent
operating cycles
operations
rated)
rated)
AC (method I)
6000
100
100
0.80
6 per minute
AC (method II)
6000
100
100
0.80
6 per minute
DC
6000
100
100
-
6 per minute
4.6.17 Short-circuit withstandability. ABT, MBT, and ABT auxiliary switches shall be tested for short-circuit
withstandability in accordance with MIL-DTL-16036. The bus transfer switches shall be subjected to and pass the
dielectric withstanding voltage test as specified in Table VII after the short-circuit withstandability tests without
adjustment, calibration, or replacement of parts. The test circuit current shall be measured, instrumented, and
calibrated in accordance with UL 1008. A 60-Hz comparison test may be used for DC and 400-Hz testing cases
where required laboratory power supplies are not available. ABTs shall fail the short-circuit withstandability tests if
one or more of the following occurs after the withstandability test:
a.
Malfunction occurs that prevents one transfer and re-transfer action by manual means.
b.
Malfunction occurs to prevent transfer and re-transfer automatically at rated conditions.
4.6.18 Dielectric withstanding voltage. Dielectric withstanding voltage tests shall be conducted in accordance
with Method 301 of MIL-STD-202. Testing shall be performed after vibration testing. Magnitude of test voltage
for circuits rated more than 60 V but not greater than 450 V, the rms test voltage shall be twice rated circuit voltage
plus 1000 V.
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