1.2 Conductor Materials: The Electrical Core

WireThe andconductor componentis the functional heart of any wire harness. Its selection isdictates anot criticalonly Designthe forelectrical Manufacturingperformance (DFM)current mandate, trading off cost, flexibility, and current-carrying capacity. Managing these material choices correctly prevents overheating,capacity, signal loss,integrity) but also the mechanical reliability of the termination. Design engineers often default to standard "hook-up wire" without considering the metallurgical and mechanical failureimplications inof the finaloperating harness.environment. A mismatch here leads to catastrophic failures: oxidation increasing contact resistance, fatigue breaks under vibration, or insulation meltdown due to improper current derating.

1.2.1 WireCopper Gauge (AWG)Metallurgy and Current DeratingPlating

WirePure size, measured in American Wire Gauge (AWG),copper is inverselythe relatedstandard conductor due to its diameter;conductivity, but it oxidizes rapidly. Plating is the mandatory defense against corrosion and is selected based on temperature and frequency requirements.

Plating Selection Matrix

Material	Temp Rating	Cost	Application Mandate
Bare Copper	Low	Lowest	Avoid in harness assembly. Oxidizes rapidly, causing high contact resistance at the crimp interface.
Tinned Copper	150˚C	Low	Standard Industry Baseline. Tin coating prevents oxidation, aids soldering, and is compatible with standard crimp terminals.
Silver-Plated	200˚C	High	High Frequency / High Temp. Excellent conductivity (Skin Effect) for RF signals. Mandatory for high-reliability aerospace.
Nickel-Plated	260˚C+	Highest	Extreme Environment. Used in engines and furnaces. Note: Harder material makes crimping more difficult; requires specialized tooling settings.

Process Note: Never mix plating types in a lowercontact AWGpair number(e.g., meansTin wire crimped to Gold terminal) without validation, as galvanic corrosion can degrade the connection.

1.2.2 Stranding Mechanics and Flexibility

Conductors are defined by their construction: Solid or Stranded. This choice is a thickertrade-off wirebetween rigidity and higherflex-life.

current

A) capacity.Solid Selectionvs. mustStranded

balance

• Solid Core: A single strand of copper. Low cost and rigid.
  • Risk: Extremely poor fatigue resistance. Prohibited in high-vibration environments (automotive, aerospace) as it will work-harden and snap.
  • Crimping: Difficult to achieve a reliable gas-tight seal; often requires soldering or IDC (Insulation Displacement Connectors).
• Stranded: Multiple smaller strands twisted together. High cost but superior flexibility and fatigue resistance.
  • Mandate: Mandatory for any application involving motion, vibration, or complex routing.

B) Stranding Geometry (Type 2 vs. Type 3)

The arrangement of strands affects the requiredwire's electricalcircularity performance withand the mechanical limitationsquality of the assembly space and connectors.crimp.

• CurrentBunched Capacity:Stranding: Strands are twisted randomly in the same direction. The primary concerncross-section is preventingirregular (not perfectly round).
  • Risk: Can lead to "hot spots" in crimps if strands shift unevenly.
• Concentric Stranding (True Concentric): Layers of strands are twisted in alternating directions. The cross-section is essentially perfectly round.
  • Benefit: Provides the most consistent, gas-tight crimp. The uniform geometry ensures even compression forces during termination.
• Rope Lay: Bundles of stranded groups twisted together. Used for large gauge power cables (e.g., 4/0 AWG) to maintain flexibility.

1.2.3 Current Capacity and Derating Rules

The "Ampacity" rating of a wire overheating,in whicha degradesdatasheet insulationis andtypically risksdefined fire.for Wiresa mustsingle bewire sizedin basedfree on the maximum required continuous current.

Derating:air Whenat multiplea specific ambient temperature (often 30˚C). In a harness, wires are bundledbundled, tightlytrapping (harnesses),heat. Using the heatdatasheet dissipationvalue isfor reduced.a Therefore,bundled theharness currentcreates a fire hazard.

The Derating Mandate

Current capacity of individual wires must be derated (reduced) based on thetwo sizefactors: ofBundle Size and Ambient Temperature.

Practical Derating Factors (Bundle Size)

When wires are bundled, the bundleinner andwires thecannot ambientdissipate operating temperature. Failing to derate is a serious safety and reliability risk.

Voltage Drop: For long harnesses or power delivery circuits, the wire gauge must be large enough (low AWG) to ensure the voltage drop (∆V) remains below the required system tolerance (e.g., 5% maximum).

1.2.2 Insulation Types and Environmental Mandates

The insulation material dictates the wire's resistance to heat, chemicals, and abrasion.heat.

InsulationNumber Typeof Current-Carrying Wires	KeyDerating CharacteristicFactor	TypicalPractical Application	MandateExample
PVC1 (PolyvinylFree Chloride)Air)	Highly1.0 flexible, low cost, good dielectric strength.(100%)	General10A purpose,rated internalwire chassiscarries wiring (low heat).	Avoid10A high-temperature areas or where chemical resistance is critical..
Polyethylene2 (PE)- 5	Excellent low-temperature performance, low dielectric loss0.8 (good for RF/High Speed).80%)	Outdoor,10A low-temperature,rated orwire data cables.	Susceptiblelimited to cracking and melting at high temperatures.8A.
PTFE6 (Teflon)- 15	Superior0.7 resistance to high heat, solvents, and abrasion.(70%)	Aerospace,10A automotiverated enginewire compartments,limited harshto chemical environments.	Mandatory7A for high-temperature or solvent exposure; higher cost..
Silicone16 - 30	Extremely0.5 flexible, wide temperature range.(50%)	Applications10A requiringrated constantwire flexinglimited orto tight bending radii.	5ALow abrasion resistance; requires mechanical protection..

1.2.3

Ambient ConnectorTemperature Family Selection

Correction

SelectingAs the correct connector is a system-level DFM decision based on environmental exposure,temperature matingrises requirements,towards andthe mechanicalinsulation's durability.rating, the allowed current drops to zero.

• Contact Plating: Plating dictates contact resistance and durability. Gold plating is mandatory for low-voltage/low-current signal integrity and high mating cycles (≥100). Tin plating is sufficient for high-current power applications and low mating cycles. Never mix tin and gold contacts in the same mated pair due to corrosion risk.
• Durability (Mating Cycles): The connector must be rated for the expected number of connect/disconnect cycles over the product's life. Standard industrial connectors may be rated for 50 cycles, while high-reliability test connectors may exceed 5,000 cycles.
• Sealing and Retention: For harsh environments, IP-rated (Ingress Protection) sealed connectors are mandatory to prevent moisture and dust ingress. Connectors must also feature locking or latching mechanisms to guarantee mechanical retention under vibration and shock.

1.2.4 Managing Wire and Component Traceability

In high-reliability manufacturing (IPC Class 3), traceability of raw materials is mandatory.

• Lot Control: Every reel of wire, batch of terminals, and lot of connectors must be tracked by its Manufacturer's Lot Number. This information must be logged against the final harness Serial Number (SN) in the MES.
• Purpose:Rule: If a defect occurs (e.g., terminal fatigue orPVC wire insulationis degradation),rated traceabilityto allows immediate quarantine105˚C and rootthe causeengine analysisbay againstis 85˚C, the specificwire only has a raw material batch20˚C used,thermal preventingheadroom. widespread field failures.
• Wire Marking: The wire itselfCurrent must be clearlydrastically identified with permanent printing (e.g., wire type, gauge, and supplier code)limited to prevent incorrect gauge insertion during manual assembly.melting.

Final Checklist: WireConductor Selection Mandates

Mandate	Criteria	RationaleVerification Action
CurrentPlating Selection	Tinned Copper is the minimum standard for general interconnects.	Verify BOM calls for tinned/plated wire to prevent oxidation-induced crimp failure.
Vibration Control	Stranded wire is mandatory for all environments subject to vibration or flexing.	Solid core is blocked from use in automotive/industrial harnesses unless specifically justified.
Crimp Geometry	Concentric stranding preferred for high-reliability crimps (Class 3).	Visual inspection of crimp cross-section (micrograph) verifies consistent strand compression.
Safety Derating	WireCurrent capacity is calculated using Derating Factors for bundle size and temperature.	Design review confirms wire gauge is deratedsufficient basedfor onthe harness bundle sizebundled andload, not just the free-air rating.
ambientGalvanic temperatureMatch	Conductor plating matches the terminal plating (e.g., Tin-to-Tin).	Prevents insulationlong-term degradationgalvanic andcorrosion fire risk due to overheating in bundled harnesses.
Connector Plating	Gold plating is mandatory for signal integrity and high mating cycles. Tin for power and low cycles.	Ensures stable contact resistance and required mating durability.
Insulation Match	Select insulation based on chemical exposure and ∆T range (e.g., PTFE for high heat/solvents).	Protects wire integrity againstat the operatingcrimp environment.
Traceability Link	Every wire and terminal lot is linked to the final harness SN in the MES.	Allows rapid quarantine and root cause analysis of material-related failures (IPC Class 3 mandate).
Voltage Drop	Wire gauge is selected to maintain the voltage drop (∆V) below the system's required tolerance (e.g., ≤ 5%).	Guarantees stable voltage supply to distant loads.interface.