crimping, interconnecting cables, harnesses, and wiring - NASA

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7. DESIGN PRACTICES 7.1 General Page 34 of 114 NASA-STD-8739.4 with Change 6 Connectors, wires, and hardware shall be selected from the Project Mission Assurance Requirements for EEE parts selection or as specified by the contract (Requirement). Harness design shall make provision for special performance requirements of any specific harness section (e.g., ease of bending, flexibility in twisting, electrical isolation, and ability to fit into confined spaces) (Requirement). Design considerations should include protective devices such as heatshrinkable sleeving for protection, stress relief, electrical insulation, and identification purposes. Precautions shall be taken to prevent the mismating of connectors, caused by interchanging or by reversing, through one of the following techniques: 7.1.1 Use of constraints that locate similar connectors built into interconnecting cables and harnesses so they cannot be interchanged (Requirement). 7.1.2 Selection of different sizes for connectors to be located adjacent to each other (Requirement). 7.1.3 Polarization or dissimilar keying of adjacent, similar connectors (Requirement). 7.1.4 Ensure clarity in marking and coding connectors (Requirement). 7.1.5 Use of confidence loop circuits to check out proper mated positions (Requirement). 7.2 Requirements Not Covered Other processes, such as potting and molding, not covered by this document may be required to fabricate cables and harnesses. The design, materials, and processes shall be defined in engineering documentation (Requirement). 7.3 Design Considerations The following considerations shall be taken in any interconnecting cable or harness design and incorporated into the design as applicable: 7.3.1 Current and voltage derating of conductors as determined from the Project Mission Assurance Requirements for EEE parts selection or as specified in the engineering documentation (Requirement). 7.3.2 Voltage drop considerations (Requirement). 7.3.3 Availability of spare connector contacts (facilitates circuitry changes) (Requirement). 7.3.4 Properties of wire insulation, lacing tape, braid sleeving, plastic strap, wrap sleeving, and plastic tubing (processibility, flammability, arc tracking resistance, vacuum stability, resistance to heat, cold flow, etc.) as appropriate for the application. Plastic straps should have metal tangs that lock securely into the "ribbed" portion of the straps (Requirement).
Page 35 of 114 NASA-STD-8739.4 with Change 6 7.3.5 Tin-plated parts (e.g., terminals, crimp barrels, etc.) must be fused or alloyed with tin-lead plating (Requirement). 7.3.6 Methods of identifying cables, connectors, and wires and their effects on environmental requirements (Requirement). 7.3.7 Radio frequency interference/electromagnetic interference (RFI/EMI) shielding requirements (Requirement). 7.3.8 Operation of circuits through critical pressure (require that potentials in excess of 200 Vac or 300 Vdc be terminated in a single-contact, high voltage connector) (Requirement). 7.3.9 Electrical wiring of redundant systems, redundant subsystems, or redundant major elements of subsystems shall not be routed in the same bundle or through the same connector with wiring of the other system, subsystem, or subsystem element (Requirement). 7.3.10 Separate handling of radio frequency (RF) signals in coaxial cable and RF connector assemblies (Requirement). 7.3.11 Materials and wiring design to meet NASA-STD-6001, Flammability, Odor, Offgassing and Compatibility Requirements and Test Procedures for Materials in Environments that Support Combustion (Requirement). 7.3.12 American wire gage (AWG) 24 wire size and larger is preferred for conductors in interconnecting cable and harness assemblies, including coaxial or triaxial cables (Requirement). High strength copper alloy shall be used for AWG 24 and smaller conductors (Requirement). When high strength copper alloy wire is used, a magnetic survey of the installation shall be conducted if project requirements indicate a sensitivity to magnetic interference (Requirement). 7.3.13 Torque values applicable for connectors, backshells, and other hardware (Requirement). 7.3.14 Route and support harnesses and cables so that they are protected from abrasion, cold flow, cut through, vibration, chafing, flexing, and sharp edges (Requirement). 7.3.15 Design minimization of splicing (Requirement). 7.3.16 Protection of all electrical terminations to withstand the operating environment (Requirement). 7.3.17 Preconditioning using thermal cycling prior to preparation for connectorization in high frequency applications using semi-rigid coaxial cable (Requirement). This procedure should also be considered for longer runs of flexible coaxial cable. 7.3.18 Confining line voltages to connectors with sockets to preclude exposing voltage points when connectors are disconnected (Requirement). 7.3.19 Specifying the use of sealing plugs and unused contacts in environmental connectors (Requirement). 7.3.20 Fabricate cables containing discrete wires in one or more layers by winding the wires together uniformly (Requirement). Whether successive layers are twisted contrahelically or unidirectionally is optional. Winding shall prevent the introduction of residual twist into
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WIRE PREPARATION: MECHANICAL STRIPP
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crimping, interconnecting cables, harnesses, and wiring - NASA

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