1.3 Insulation & Cable Structures: Environmental Armor

If the conductor is the heart of the harness, the insulation and cable structure are its skin and skeleton. They define the harness's ability to survive the physical reality of the application—heat, abrasion, chemicals, and electrical noise. A failure here is just as catastrophic as a broken wire; a cracked jacket leads to shorts, while crushed dielectric destroys signal integrity.

1.3.1 Insulation Chemistry: The First Line of Defense

Insulation selection is a balance between thermal range, mechanical toughness, and dielectric properties.

Material Selection Matrix

Material	Temp Range	Key Strength	Key Weakness	Typical Use
PVC (Polyvinyl Chloride)	-20˚C to +105˚C	Low cost, flexible, easy to strip.	Melts easily (soldering risk); poor cut-through resistance; brittle in extreme cold.	Standard consumer/industrial wiring (UL 1007/1015).
XLPE (Cross-Linked PE)	-40˚C to +125˚C	Tougher than standard PVC; resists melting during soldering.	Stiffer than PVC; harder to strip without nicking strands.	Automotive engine bay (GXL/TXL), power distribution.
PTFE (Teflon)	-60˚C to +260˚C	Chemical inertness (fuel/oil), non-flammable, low friction, excellent dielectric.	High cost; prone to "cold flow" (creep under pressure); requires specialized stripping blades.	Aerospace, military, high-temp industrial.
Silicone	-60˚C to +200˚C	Extreme flexibility; high voltage resistance.	Very poor abrasion resistance (soft); easily cut or torn during installation.	High-voltage leads, robotics, flexible joints.

Process Mandate: Production tooling must be matched to the chemistry. PVC strips easily with V-blades, while PTFE and XLPE often require die-blades or rotary strippers to prevent conductor damage due to the force required to cut the tough insulation.

1.3.2 Complex Cable Anatomy: Structure and Risks

Beyond single wires, complex cables introduce geometry that controls electrical performance. Altering this geometry during processing destroys the cable's function.

A) Coaxial Cables (RF Signals)

Coaxial cable performance relies on the precise concentric spacing between the center conductor and the shield, maintained by the dielectric.

Structure: Center Conductor – Dielectric – Shield (Braid/Foil) – Jacket.
Processing Risk (Crushing): Using a clamp or tie-wrap that is too tight crushes the soft dielectric (e.g., foam PE). This changes the capacitance and impedance at that spot, causing signal reflection (VSWR failure).
Stripping Risk: Cutting too deep slices the shield strands; cutting too shallow leaves dielectric residue on the center pin. Rotary stripping machines are mandatory for repeatability.

B) Twisted Pair (Differential Signals)

Twisted pairs (e.g., CAN bus, Ethernet) reject electromagnetic interference (EMI) via their specific twist rate (lay length).

Untwisting Limit: When terminating, the "untwist" length must be minimized (typically ≤ 13 mm or 0.5 inch) to maintain noise rejection. Excessive untwisting creates an "antenna" for noise right at the connector.

C) Shielded Cables (EMI Protection)

Shields (foil or braid) contain internal noise and block external noise.

Termination: The shield must be terminated 360 degrees (via backshell) or via a drain wire. Pigtailing (twisting the braid into a wire) introduces high inductance and should be kept as short as possible.
Stripping Risk: Slicing the shield during jacket removal breaks the ground path. Using a scribe-and-break technique or thermal stripping avoids this damage.

1.3.3 Ribbon and Flat Flex Cables (FFC)

Flat cables offer high density and repeated flexing but are mechanically fragile.

A) Pitch Definitions

Pitch is the center-to-center distance between conductors.

Ribbon Cable: Standard pitch is 1.27 mm (0.050 inch) designed for IDC (Insulation Displacement Connectors).
FFC (Flat Flexible Cable): Common pitches are 0.5 mm and 1.0 mm.

B) Processing Risks

Scribing/splitting: Separating ribbon cable conductors for discrete termination requires a slitter that cuts precisely between wires. Misalignment exposes the conductor, creating a short risk.
FFC Contact Damage: FFC contacts are thin and plated. Manually forcing an FFC into a Zero Insertion Force (ZIF) connector can peel the plating fingers (gold/tin) back, ruining the connection.
Creasing: FFCs are designed for rolling flex, not hard creasing. A "hard fold" fractures the thin copper tracks permanently.

Final Checklist: Cable Structure Mandates

Mandate	Criteria	Verification Action
Material Match	Insulation rated for the environment (e.g., PTFE for solvents, XLPE for heat).	BOM check against environmental requirements specification.
Stripping Integrity	Rotary stripping used for Coax/Shielded cables; no nicked shields.	Visual inspection under magnification (10 times) for broken braid strands or sliced dielectric.
Coax Geometry	Dielectric must remain round and uncrushed.	Impedance/VSWR test or visual inspection of clamping points (no deformation).
Twist Maintenance	Twisted pairs maintained up to ≤ 13 mm from termination.	Visual audit of the connector backend to verify twist integrity.
FFC Handling	No hard creases; contacts pristine (no peeled plating).	Visual inspection of FFC fingers before insertion into ZIF connectors.