MIL-PRF-22594C(SH)
4.5.1 Heating elements. Heating elements of each watt density shall be subjected to the tests specified in
4.5.1.1 Moisture resistance. The element shall be completely immersed in water and while immersed,
subjected to a hydrostatic gage pressure of at least 60 pounds per square inch for a period of at least 20 minutes.
Terminals of the element shall be wiped dry and subjected to the dielectric test of 4.5.1.2 and the insulation
resistance test of 4.5.1.3.
4.5.1.2 Dielectric strength. The element shall be subjected to and shall withstand, for a period of 1 minute, a
dielectric test voltage of twice the rated line voltage plus 1,000 volts applied between the terminal and the sheath.
The voltage wave shall be in accordance with 3.12.1.1.
4.5.1.3 Insulation resistance. Insulation resistance shall be measured to determine conformance with 3.12.1.2
as follows:
a.
Insulation resistance (cold) at ambient room temperature.
b.
Insulation resistance (hot) after heating element has been energized for at least 10 minutes or has
reached a temperature of 450 ºF, deenergize heater and take hot insulation resistance within 60 seconds
of removing electrical power.
4.5.1.4 Accelerated life test. Accelerated life test by fusion shall be conducted as follows:
a.
Support element in still air.
b.
Apply voltage so that element is operating at rated wattage.
c.
When operating temperature is stabilized, operate at this condition for at least 30 minutes, cycling
on/off at 5-minute intervals.
d.
Increase voltage to the next higher increment of 5 WSIA, excluding the fins.
e.
Read and record voltage and wattage, and operate the element at this level for at least 30 minutes,
cycling on/off at 5-minute intervals.
f.
Repeat steps d and e until element fails by fusion or 90 WSIA is reached, whichever occurs first.
4.5.2 High limit cutout switch. Each high limit cutout switch shall be tested to show that the switch opens
within 15 °F of the design temperature set point as specified in 3.12.2.
4.5.3 Vibration tests. Vibration tests on the heater assembly shall be conducted prior to the shock test specified
in 4.5.4 and performance tests specified in 4.5.5. The heater assembly shall be subjected to the Type I
environmental tests specified in MIL-STD-167-1.
4.5.4 High-impact shock tests. Size 32EH heater and smaller shall be shock tested on the lightweight machine
as prescribed for Grade A shock of MIL-S-901. Size 33EH heater and larger shall be shock tested on the medium
weight machine as prescribed for Grade A shock of MIL-S-901. The heater shall be operated at rated voltage and
current during the shock tests. Correction of damage which may have occurred during the shock test shall not be
performed prior to conducting the tests specified in 4.5.5. Evidence of fragmentation or missile effect of parts or
failure to operate shall be cause for rejection.
4.5.5 Heater performance tests. Performance tests shall be conducted in accordance with 4.5.5.1 through
12
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