MIL-DTL-15291G
4.7.6 Overload. The switches shall be operated for 50 operations to interrupt 600 percent of the rated
alternating current at the rated voltage. The circuit shall provide for ON-OFF switching and one operation
shall consist of throwing the switch from the OFF to the ON position and returning to the OFF position.
The test rate shall be 2 operations per minute and the duty cycle shall be 50 percent ON and 50 percent
OFF (applicable to 1SR and 3SR only).
4.7.7 Contact resistance. Contact resistance between the stationary contacts which have been
energized for the endurance tests (see 4.7.9), shall be determined in accordance with method 307 of MIL-
STD-202, and the exceptions listed herein. The following details shall apply:
a. Test leads shall be connected by a method suitable for the switch terminals.
b. Test current and voltage shall be the rated current and voltage energizing the switch during
the endurance tests (see tables VIII and IX).
c. Prior to each measurement, the switch shall be operated once.
d. Five separate measurements shall be taken at each interval and the average value
calculated.
e. The contact resistance shall be determined prior to the endurance tests, and during the
endurance tests at intervals of: 5000 operations for classes 1SR and 1SRN, 4000
operations for class 3SR and at 1000 operations for classes 6SR and 20SR.
4.7.8 Temperature rise. The temperature rise of the switch stationary contacts energized during the
electrical endurance tests shall be determined by means of thermocouples of small wire gauge (28-32
AWG). The temperature sensitive elements shall be placed on the contacts where they first emerge from
the switch body. Temperature measurements shall be taken immediately following the electrical
endurance test. The contacts shall be energized at rated current at any convenient voltage within the
switch rating. Temperature measurements shall be taken at half-hour intervals until three successive
measurements are within plus or minus 1 °C.
4.7.9 Endurance.
4.7.9.1 Alternating current. Referring to the columnar headings of table VIII, the switch shall make,
break, and carry (a) amperes at (b) volts at unity power factor for a total of (c) operations (see 6.2). The
rate of testing shall not exceed (d) operations per minute. An operation is defined as one make and one
break, of the same switch contact and the number of operations is determined by the contact either
movable or stationary which is subjected to the largest number of makes and breaks. Following this, the
switch shall be de-energized and operated for additional (e) operations. The duty cycle shall be 50
percent ON and 50 percent OFF.
TABLE VIII. AC endurance.
(a)
(b)
(c)
(d)
(e)
Switch
Current
Voltage
Electrical
Test rate
De-energized
class
(amperes
(volts rms)
operations
(operations
operations
rms)
(number of
per minute)
(number of
operations)
operations)
1SR
10
125
30,000
30
20,000
1SRN
10
125
20,000
30
10,000
3SR
30
500
20,000
30
10,000
6SR
60
500
6,000
10
4,000
20SR
200
500
6,000
8
4,000
4.7.9.1.1 Test wiring. The test wiring for qualification testing shall be in accordance with figure 1 (see
6.2). For tests involving type designations other than the SR3B, the wiring for qualification testing shall
simulate an intended switch application.
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