MIL-PRF-26 Resistors, Fixed, Wire Wound \(Power Type\) General Specification ForThis specification covers the general requirements for power type, wirewound, fixed resistors for use in electrical, communications, and associated equipment. Included are general purpose styles of 5 percent initial resistance tolerance, with power ratings ranging from 3 watts to 240 watts at 25 Degrees C, derated to 0 power at 350 Degrees C \(characteristics N and V\) and precision axial lead types of .1\(B\) percent, .5 \(D\)percent, and 1 \(F\) percent initial resistance tolerances with power ratings ranging from 1 watt to 10 watts at 25 Degrees C, derated to 0 power at 250 degrees C \(characteristic U\).

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MIL-PRF-26H

Measurement after test: DC resistance as specified in 4.7.2.

Inspection after test: Resistors shall be inspected for evidence of breaking and loosening of terminals and

chipping of coating or other evidence of mechanical damage.

4.7.7 Resistance-temperature characteristic (see 3.11). Resistors shall be tested in accordance with method 304

of MIL-STD-202. The following detail shall apply. Test temperature: In accordance with table VI.

4.7.8 Dielectric withstanding voltage (see 3.12).

4.7.8.1 Atmospheric pressure. Resistors shall be tested in accordance with method 301 of MIL-STD-202. The

following details and exceptions shall apply:

Special preparations:

(1) Tab terminals: Flat (stack mounting) resistors shall be completely equipped with mounting hardware,

but without supplementary mounting insulation.

(2) Tab terminals: Tubular resistors shall be mounted without supplementary insulation, between two metal

plates normal to the longitudinal axis of the resistor, one plate at each end, held firmly against the end

of the resistor core by a through-bolt. These plates shall be of sufficient size to extend beyond the

resistor terminal extremities.

(3) Axial lead terminals: Resistors shall be placed in a conductive material which will conform to the

resistor surface so that at least 90 percent of the outer periphery is contacted.

Initial measurement: DC resistance shall be measured as specified in 4.7.2.

Magnitude of test voltage: 1,000 volts rms for all styles except RW70, RW80, and RW81; for styles RW70,

RW80, and RW81, the potential shall be 500 volts rms.

Nature of potential: AC supply at commercial-line frequency and waveform.

Duration of application of test voltage: 1 minute.

Rate of application of test voltage: The test voltage shall be raised from zero to 1,000 (500 for RW70,

RW80, and RW81) volts rms, as uniformly as practicable, at a rate of approximately 100 volts rms per

second.

Points of application of test voltage: Between the resistor terminals connected together and the mounting

hardware, or the conductive material on the axial-lead resistors, as applicable.

Measurement after test: DC resistance shall be measured as specified in 4.7.2.

Inspections after test: Resistors shall be inspected for evidence of flashover, mechanical damage, arcing,

and insulation breakdown.

4.7.8.2 Barometric pressure (reduced) (as applicable, see 3.1). Resistors shall be tested in accordance with

method 105 of MIL-STD-202. The following details and exceptions shall apply:

Method of mounting: As specified in 4.7.8.1.

Initial measurements: DC resistance shall be measured as specified in 4.7.2.