MIL-DTL-55668D
4.7.12 Retraction at 85 C. The test specimen shall be a completed cord. With the helical section
extended to three times its retracted length, the cord shall be conditioned in a circulating air oven
maintained at 851 C for 20 hours. At the end of this period and while in the oven at 85 C, the helical
section shall be extended further, to five times its retracted length, and returned to its original retracted
length. The extension and retraction shall be repeated for a total of three cycles. The cord shall then be
suspended vertically and measured for retraction at the end of 15 seconds the percent retraction
(calculated based on original horizontal retracted length) shall meet the requirements specified in table III.
4.7.13 Voltage withstand. The finished retractile cord, or convenient length of straight cord, as
applicable, shall be immersed in tap water, at room temperature, for at least 9 hours prior to testing.
During the test, neither the extreme ends of the cord nor the bared conductor wires shall be immersed in
water. Cord shall meet the requirements of table IV.
4.7.13.1 High-voltage source. The voltage withstand test shall be made with an alternating potential of
commercial power frequency, having a wave form as nearly sinusoidal as practicable. The testing
transformer and power source shall be capable of supplying no less than 3.0 kVA.
4.7.13.2 Voltage measurements. The testing voltage may be measured by any approved method which
gives a root-mean-square value, preferably by means of a voltmeter connected to a special voltmeter coil
in the high-voltage winding of the testing transformer or to a separate step-down transformer. A voltmeter
on the low-voltage side of the transformer is satisfactory, provided the ratio of transformation does not
change under any test condition.
4.7.13.3 Procedure. An alternating potential as specified in table IV shall be applied between two
terminals, one being each conductor in turn, and the other being all the remaining conductors tied
together in electrical contact with the water. The initially applied voltage shall be no greater than 600
volts, and the rate of increase shall be approximately uniform and not over 100 percent in 10 seconds,
nor less than 100 percent in 60 seconds. The specified test voltage shall be applied for not less than one
minute unless breakdown occurs prior to that.
4.7.14 Insulation resistance. The insulation-resistance measurements shall be made on sample units
which have successfully passed the voltage withstand test (see 4.7.13). The apparent insulation
resistance shall be measured as soon as practicable after the voltage withstand test. The leakage
current shall be measured after a 1-minute electrification with a direct-current potential of not less than
100V or more than 500V. The polarity of the conductor wire shall be maintained negative with respect to
the water. The insulation resistance of each cord shall be measured as follows: A direct current potential
shall be applied between two terminals: (1) one terminal shall be all the conductors and shield wires tied
together, and the other shall be the jacket surface which is in electrical contact with the water; (2) one
terminal shall be each conductor wire in turn, and the other shall be all the remaining conductors plus all
shield wires tied together in electrical contact with the water. If measurements are made at lower than 20
C, the measured value of each resistance shall be corrected to 20 C. The minimum resistance value
°
per cord shall be as specified in table IV.
4.7.15 Continuity. Each conductor and shield of each length of finished cord or cord on reel, as
applicable, shall be tested for continuity. The maximum test voltage shall be 10 volts (see table IV).
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