CABLE AND HARNESS GENERAL REQUIREMENTS (2024)

PREFERRED

BACKSHELL

Connector backshells shall be potted and molded, or use stress relief boots as required, in accordance with applicable engineering documentation.

NASA-STD-8739.4 [13.1.1.c]

PREFERRED

BEND RADIUS

Cables and harnesses shall not be subjected to bending forces resulting in radii less than the minimum specified for the most sensitive component (i.e.: coaxial, fiber, etc.) in the assembly.

Best Workmanship Practice

PREFERRED

COAXIAL/FIBER OPTIC CABLE LOCATION

Harnesses should be designed so that coaxial/fiber optic cables are located at or near the bundle center to minimize flexure and to provide additional protection.

Best Workmanship Practice

PREFERRED

COAXIAL/FIBER OPTIC CABLES

Coaxial cable (flexible, semi-rigid, rigid) and fiber optic cables shall exhibit a neatly organized layout, with smooth bends and sufficient stress relief.

Best Workmanship Practice

PREFERRED

CONNECTOR STYLE

Connectors shall be straight, right-angle or flange-mount. The use of right-angle connectors shall be minimized and restricted to applications where stress-free mounting of the cable assembly can be assured.

Best Workmanship Practice

PREFERRED

DISCRETE WIRE HARNESSES

Harnesses exhibit a neatly organized layout with smooth bends and sufficient stress relief. Connector cable clamps and cable straps are properly set.

NASA-STD-8739.4 [19.6.1.e]

PREFERRED

DUST CAPS

The mating surfaces of all unmated connectors shall be protected by covers during storage, handling and installation. Connectors on ESD sensitive hardware shall be protected by ESD rated dust caps/covers.

NASA-STD-8739.4 [13.1.2], [16.2.4], [16.3.3]

PREFERRED

HYBRID CABLES/HARNESSES

Hybrid cables/harnesses (copper/fiber optic/coaxial conductors) shall be designed to comply with the requirements of the most sensitive and demanding component (typically the fiber optic cable) in the assembly.

Best Workmanship Practice

PREFERRED

IDENTIFICATION
CABLES/HARNESSES

Each cable/harness shall be identified by a permanent label/marking.

NASA-STD-8739.4 [14.2.1]

PREFERRED

IDENTIFICATION
CONNECTOR

Each connector shall be identified by a permanent label/marking affixed directly to the connector body, or to the cable adjacent to the connector.

NASA-STD-8739.4 [14.2.2]

PREFERRED

POLARIZATION/KEYING

Interconnecting cables and harnesses shall be designed with physical constraints (keying, sizing, polarization, etc.) to prevent incorrect mating/interchanging with similar sized/colored connectors.

NASA-STD-8739.4 [7.1]

PREFERRED

RIBBON CABLE

The cable assembly meets dimensional, layout and design requirements and exhibits a smooth, flat profile with no visible damage to the connectors or the insulation. Connectors are properly aligned and seated.

Best Workmanship Practice

PREFERRED

SHIELD TERMINATION - FLOATING

Heat shrink tubing is properly installed, tightly shrunk and the termination is visible. Overlaps are of sufficient length to meet minimum electrical spacing.

NASA-STD-8739.4 [9.8.1], [9.9], [11.5], [19.6.1]

PREFERRED

SHIELD TERMINATION - GROUNDED

Heat shrink sections are properly installed, tightly shrunk and the termination is visible. Overlaps meet minimum electrical spacing. Ground wire exhibits proper bend radius and strain relief.

NASA-STD-8739.4 [7.3.22], [9.8.1], [9.9], [11.5], [19.6.1]

ACCEPTABLE

SPOT TIES

Spot ties shall consist of a clove hitch, followed by a square or other similar non-slip knot (i.e.: surgeon, etc.).

NASA-STD-8739.4 [9.2.2]

ACCEPTABLE

BACKSHELL ASSEMBLY

Connector backshells, adapters and clamps shall be assembled and torqued per engineering documentation.

NASA-STD-8739.4 [13.5]

ACCEPTABLE

BACKSHELL SCREW PROTRUSION

Screws shall protrude a minimum of 1-1/2 threads beyond the threaded hardware (e.g., nut, clamp, etc.), but shall not violate minimum electrical spacing or snag requirements, unless otherwise specified by engineering documentation.

Best Workmanship Practice

UNACCEPTABLE

EXCESSIVE THREAD PROTRUSION

Excess thread protrusion represents an assembly, interference and electrical separation problem, as well as adds unnecessary weight to the assembly.

Best Workmanship Practice

ACCEPTABLE

BREAKOUT DRESS W/ FABRIC BRAID

Braiding shall be dressed to form a smooth profile across the breakout. Braiding shall not be split, slit or punctured to provide a breakout opening.

NASA-STD-8739.4 [9.3]

UNACCEPTABLE

SPLIT/SLIT BRAIDING AT BREAKOUT

Braiding shall not be split, slip or punctured to provide an opening at the breakout.

NASA-STD-8739.4 [9.3]

ACCEPTABLE

CABLE LACING
RUNNING STITCH

The lacing begins and ends with a knot. Wraps are properly spaced (relative to harness diameter) to maintain the wiring in a tight, neat bundle. Ends are properly trimmed.

NASA-STD-8739.4 [9.2]

UNACCEPTABLE

CABLE LAYUP

Cables containing discrete conductors shall be fabricated in one or more layers, by winding the conductors together uniformly. Layup (twist) of each layer shall be 8-16 times the outer harness diameter.

NASA-STD-8739.4 [7.3.20], [19.6.1.e.4]

ACCEPTABLE

CABLE LACING
SPOT TIES

Ties are neat, tight and properly spaced (relative to harness diameter) to maintain the wiring in a tight, neat bundle. Ends are properly trimmed.

NASA-STD-8739.4 [9.2.2]

UNACCEPTABLE

LOOSE CABLE LACING

The lacing has not been properly installed, resulting in a loose, unorganized bundle.

NASA-STD-8739.4 [19.6.2.d.4]

ACCEPTABLE

CABLE STRAPS/TIES

Plastic straps should have metal tangs that lock securely into the ribbed portion of the strap.

NASA-STD-8739.4 [7.3.4]

ACCEPTABLE

CONDUCTOR DRESS

All wires are dressed with even bends and sufficient strain relief. Conductor crossover is minimized.

NASA-STD-8739.4 [19.6.1.e]

ACCEPTABLE

CABLE TIES/TIE WRAPS

The cable ties/tie wraps are sufficiently tight to prevent lateral movement along the cable bundle under normal handling, but can be rotated in place. Strap ends have been trimmed off square and flush with the face of strap head.

NASA-STD-8739.4 [9.6]

UNACCEPTABLE

UNTRIMMED CABLE TIES

The strap end shall be trimmed off, flush with the back end of the strap head.

NASA-STD-8739.4 [9.6], [19.6.2.d.5]

ACCEPTABLE

CONNECTOR SAVERS

The use of connector savers is recommended. Connector savers shall meet the same requirements as a flight connector.

NASA-STD-8739.4 [17.2.7]

ACCEPTABLE

DIRECT WEAVE FABRIC BRAID

Fabric braids woven directly on interconnecting harnesses or cables may be loose or tight. The finish shall be smooth, without gaps in coverage, and without frayed ends.

NASA-STD-8739.4 [9.4]

ACCEPTABLE

DISCOLORATION/SCUFFING
CONNECTOR

Slight scuffing or discoloration is acceptable, provided there is no impact to form, fit or function, and there is no exposure of base metal.

Best Workmanship Practice

ACCEPTABLE

DISCOLORATION/SCUFFING
INSULATION

The cable does not exhibit evidence of insulation damage, such as cuts, nicks, scrapes, crushing, cold flow or burns. Slight scuffing or discoloration is acceptable.

NASA-STD-8739.4 [19.6.2.e.9]

ACCEPTABLE

FABRIC BRAIDED SLEEVING

Prewoven fabric (unvarnished) braid sleeving may be installed over the wire harness. Sleeving shall be snug, secured at both ends and shall not slide freely. Ends shall not be frayed or unraveled, and shall be tucked under.

NASA-STD-8739.4 [9.3]

ACCEPTABLE

FABRIC BRAID SLEEVING
ALTERNATE END DRESS

The end of the braid may be secured by connector clamps, other hardware or potting.

NASA-STD-8739.4 [9.3.2]

ACCEPTABLE

FABRIC BRAID SLEEVING
BASIC END TERMINATION

The end of the braid shall be tucked under and secured with a spot tie or plastic strap.

NASA-STD-8739.4 [9.3.1]

ACCEPTABLE

GLASS BRAID SLEEVING

The ends of glass braid may be bonded by use of adhesive, and then secured by spot tie or other means to prevent movement on the wire bundle.

NASA-STD-8739.4 [9.3.3]

ACCEPTABLE

GROUP SHIELD TERMINATION

Shield ground leads shall be terminated to a common ground point. No more than 4 conductors, plus a drain wire, shall be terminated in a single splice.

NASA-STD-8739.4 [11.6]

UNACCEPTABLE

DAISY-CHAIN GROUND TERMINATION

Shield ground leads terminated in a dasy-chain configuration are susceptible to a single-point failure, should one of the links break.

NASA-STD-8739.4 [19.6.2.f.2]

ACCEPTABLE

HEAT SHRINKABLE SLEEVING

Sleeving shall be sized to provide a tight, smooth finish in the area of maximum diameter. Tubing shall be uniformly shrunk, without cracks, punctures, charred, burns or wrinkles.

NASA-STD-8739.4 [9.8.1], [9.11], [19.6.1.e.13]

ACCEPTABLE

HEAT SHRINK TUBING AS STRESS RELIEF

The sleeving covers the termination and extends a minimum of 5 mm (0.20 in.) over the wire insulation. Tubing is fully shrunk, tight and sufficiently rigid to provide stress relief and prevent flexure at the solder termination.

NASA-STD-8739.4 [9.9], [Fig. A]

ACCEPTABLE

IDENTIFICATION

Each cable/harness shall be identified by a permanent label/marking. Each connector shall be identified by a permanent label/marking affixed directly to the connector body, or to the cable adjacent to the connector.

NASA-STD-8739.4 [14.2.1], [14.2.2]

ACCEPTABLE

IN-LINE SPLICE

The splice exhibits a smooth profile, proper strain relief and is located in an area of the harness not subjected to flexure.

Best Workmanship Practice

ACCEPTABLE

INSULATION WRAP

Non-conductive tape/insulation wrap may be used in applications in which the use of heat-shrinkable tubing is impractical. Tape and wrapping materials shall be installed per engineering documentation.

Best Workmanship Practice

ACCEPTABLE

METAL BRAID SLEEVING

Metal braid sleeving may be installed over harnesses by either direct weave or by use of prewoven tubing. An insulation/separation layer shall be installed between the harness and the metal braid.

NASA-STD-8739.4 [9.7]

ACCEPTABLE

OVERALL HARNESS SHIELDING

An overall braided metallic shield provides mechanical and electrical protection (EMI/RFI) to the harness. Metallic shielding shall exhibit a smooth and tight finish, with a uniform distribution of coverage and no projecting strands.

NASA-STD-8739.4 [11.1.3]

ACCEPTABLE

POLYIMIDE/NYLON BRAID SLEEVING
HOT KNIFE SEALING

Polyimide or nylon braids (for use on ground support equipment) may have their ends sealed by use of a "hot knife" or similar instrument.

NASA-STD-8739.4 [9.3.4]

ACCEPTABLE

SHIELD/DRAIN WIRE

The shield and drain wire have been properly terminated, per engineering documentation.

NASA-STD-8739.4 [19.6.1.f.2]

ACCEPTABLE

SPIRAL WRAP SLEEVING

Spiral wrap shall be tight, uniformly spaced and shall not overlap. Ends shall be trimmed to eliminate sharp edges.

Note: Spiral wrap shall not be used on spacecraft or launch vehicles.

NASA-STD-8739.4 [9.5]

ACCEPTABLE

SOLDER SLEEVE TERMINATION

The solder sleeve has been properly installed and tightly shrunk. Strain relief is acceptable. Overlaps are of sufficient length to meet minimum electrical spacing. Solder fillet is visible, fully flowed and smooth.

NASA-STD-8739.4 [11.4]

UNACCEPTABLE

SOLDER SLEEVE TERMINATION

The solder sleeve has not been completely shrunk and is improperly positioned, resulting in a poor fit that does not provide a good mechanical grip or seal, and which does not meet minimum overlap requirements.

NASA-STD-8739.4 [9.8.1], [9.11]

ACCEPTABLE

SPLICE ASSEMBLY PROFILE

The location of splices shall be staggered to minimize the increase in profile to the harness. Final assembly profile shall not impact form, fit or function.

Best Workmanship Practice

ACCEPTABLE

STRAIN RELIEF

The cable (shield/unshielded) should be dressed to ensure that the strain relief mechanism transfers structural stresses from the connector to the cable sheath (or strength member) rather than to the individual conductors.

Best Workmanship Practice

ACCEPTABLE

SPLICE/SOLDER SLEEVE RESTRAINT

Cable ties/lacing shall be installed at both ends of a splice or solder sleeve, but placement shall not violate stress relief requirements.

Best Workmanship Practice

UNACCEPTABLE

SPLICE/SOLDER SLEEVE RESTRAINT

Cable ties/lacing shall not be installed across the splice/solder sleeve body, unless sufficient protection is provided to prevent compression damage to the termination and/or to the insulation of adjacent conductors.

Best Workmanship Practice

ACCEPTABLE

STRESS RELIEF

Wires exiting from the connector shall be stress relieved.

NASA-STD-8739.4 [7.3.22]

UNACCEPTABLE

INSUFFICIENT STRESS RELIEF

The placement of cable ties/straps shall not negate strain relief in cables or harnesses.

Best Workmanship Practice

ACCEPTABLE

TIE/WRAP SPACING

Ties are neat, tight and properly spaced (relative to harness diameter) to maintain the wiring in a tight, neat bundle.

NASA-STD-8739.4 [9.2], [19.6.1.e.5]

UNACCEPTABLE

INCORRECT TIE SPACING

Cable ties/wraps have not been properly spaced relative to bundle/harness diameter.

NASA-STD-8739.4 [19.6.2.d.7]

ACCEPTABLE

TIE/WRAP SPACING AT BREAKOUT

Lacing or tie wraps have been placed on both sides of the harness breakouts. Ties are neat and tight.

NASA-STD-8739.4 [9.6]

ACCEPTABLE

UNIFORM CONDUCTOR TENSION

The conductors exhibit uniform tension throughout the length of the harness. No bunching, bowing, looping, kinks, etc.

NASA-STD-8739.4 [19.6.1.e.3]

ACCEPTABLE

UNUSED/SPARE CONDUCTORS

Unused or spare conductors shall be terminated by folding the unstripped end back on itself and then sealed with insulation sleeving or wrap. Conductor ends shall be secured to prevent unwanted movement, protrusion or snagging.

NASA-STD-8739.4 [19.6.1.e.19]

UNACCEPTABLE

DAMAGE
CONNECTOR

Damage to the connector (i.e.: cuts, gouges, cracks, deformed features, bent pins, exposed base metal, etc.).

NASA-STD-8739.4 [19.6.1.e.1]

UNACCEPTABLE

DAMAGE
INSULATION

Damage to the cable jacket, ribbon or conductor insulation (i.e.: cuts, pinching, nicks, scrapes, crazing, crushing, cold flow, exposed conductors, punctures, thinning or burns).

NASA-STD-8739.4 [19.6.2.e.9]

UNACCEPTABLE

EXPOSED POWER CONTACTS

Active signal/live voltages shall be confined to connectors with sockets to preclude the exposure of voltage points when the connector is disconnected.

NASA-STD-8739.4 [7.3.18]

UNACCEPTABLE

IMPROPER BEND RADIUS

The harness exhibits a bend radius that is less than the minimum recommended for the conductor type(s) used and overall harness diameter.

NASA-STD-8739.4 [7.3.21]

UNACCEPTABLE

IMPROPER CABLE TIE/WRAP TENSION

Cable tie/wrap tension is too loose, allowing lateral movement along the cable bundle under normal handling.

NASA-STD-8739.4 [19.6.2.d.4]

UNACCEPTABLE

IMPROPER CABLE TIE/WRAP TENSION

Cable tie/wrap tension is too high, resulting in deformation and pinching of the wire insulation.

NASA-STD-8739.4 [19.6.2.d.3]

UNACCEPTABLE

IMPROPER LACING KNOT

The cable lacing has been secured with a bow-knot, rather than a square/non-slip knot. This tie may eventually loosen.

NASA-STD-8739.4 [19.6.2.d.4]

UNACCEPTABLE

IMPROPER ROUTING

Cables and harnesses shall be routed so that they are protected from abrasion, cold flow, cut through, vibration, chafing, flexing and sharp edges.

NASA-STD-8739.4 [7.3.14]

UNACCEPTABLE

IMPROPER SPLICE GAUGE/SIZE

Replacement conductors shall be of the same voltage and current rating as the original conductor.

Best Workmanship Practice

UNACCEPTABLE

IMPROPER TERMINATION

Solder and/or crimped terminations that do not meet the requirements of NASA-STD-8739.3 and/or NASA-STD-8739.4 shall be cause for rejection.

NASA-STD-8739.4 [13.1]

UNACCEPTABLE

INCOMPLETE COVERAGE OF METAL BRAID

Metal braid sleeving shall exhit uniform coverage, to provide electrical and mechanical protection to the underlying harness.

NASA-STD-8739.4 [19.6.2.b.8], [19.6.2.e.5]

UNACCEPTABLE

INCORRECT LACING MATERIAL

Waxed lacing shall not be used for spaceflight applications.

NASA-STD-8739.4 [19.6.2.d.2]

UNACCEPTABLE

PROJECTING SHIELD STRANDS

The shield strands have been improperly dressed, resulting in projecting strands that may result in an electrical short or sharp object (punture/snag) concern.

Best Workmanship Practice

UNACCEPTABLE

SPLICES IN FLEXURE ZONE

Splices shall not be installed in areas where the harness is designed to flex.

Best Workmanship Practice

UNACCEPTABLE

UNSEALED ENVIRONMENTAL CONNECTOR

Sealing plugs or unused pins shall be installed in all unwired/unused holes to retain the environmental rating of the connector.

NASA-STD-8739.4 [7.3.19]