MIL-STD-981C
5.5.12.5 Crossover of turns. There shall be no uninsulated crossover of any one turn in any one layer of insulated interleaved layer-wound coils, nor crossover to the adjacent winding segment of toroidal or cylindrical coils wound in segments.
5.5.12.6 Splices. There shall be no splicing of magnet wires of the same winding or lead wires of the same size. The solder connection of the magnet wires between windings or series connection of
designed multi-wound series windings or to lead wire shall not be regarded as a splice within the definition of this section.
5.5.12.7 Extraneous material. There shall be no evidence of extraneous material:
a. In the path of leakage currents, such as: terminal-to-terminal, terminal-to-adjacent winding, terminal-to metallic case, and winding-to-core. (See Figure B-3.)
b. In coil margins, in layer-to-layer or winding-to-winding insulation. (See Figure B-7a, B-8 and B-9).)
5.5.12.8 Cores.
a. Laminated cores ("C" cores, laminations, etc.) shall not show excessive distortion, misalignment of pole faces, foreign material, or excessive spacing in the gap, loose or bent laminations, or any other anomaly.
b. Ferrite and powder cores shall be free of cracks and chips. Chip-outs, as a result of manufacturing, smaller than 0.02 inch in the largest dimension that do not reduce
the cross section of the magnetic path by more than 5 percent shall be acceptable.
c. All molypermalloy powder cores (MPP) shall be coated by phenolic resin or epoxy impregnation to provide a minimum breakdown of 500 V rms.
d. Toroidal cores encased in sealed protective boxes shall show no evidence of damage or defect that may allow leakage of the damping medium or introduction of foreign material.
5.5.12.8.1 Protective coating. When possible ferrite and powder toroidal cores shall be of epoxy or parylene coated type or shall be tape wrapped prior to winding. Wire shall be protected from possible abrasion in areas of contact with core.
5.5.12.9 Rejection criteria. Devices which fail to meet one or more of the requirements specified shall be removed from the lot and shall not be shipped.
5.5.13 Impregnation and potting.
5.5.13.1 Drying. Prior to impregnation and potting, all devices shall be dried at sufficient temperatures and for sufficient length of time to minimize the moisture and to cure all tapes. The vacuum drying of devices is preferred. The devices shall be impregnated within 20 minutes after being removed from the drying oven or vacuum chamber. If this is impractical, the devices shall be stored in controlled dry atmosphere. If the devices were exposed to a relative humidity in excess of 30 percent for 30 minutes or more, they shall be re-dried at sufficient temperature and for a sufficient length of time to minimize the moisture.
5.5.13.2 Impregnation. Each device shall be impregnated in an appropriate chamber or molded to assure thorough, void-free impregnation "when practical".
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