1.1 Quality Baseline: IPC/WHMA-A-620 Classes

Requirements and environmental conditions form the foundation of cable harness design. A harness may look flawless on the bench, yet its true performance is measured over years of vibration, heat cycles, and exposure to chemicals or electromagnetic interference. By mapping electrical, mechanical, thermal, and regulatory demands up front, engineers ensure that every material and routing choice supports long-term reliability. The goal is a design that disappears into the background, working silently without maintenance or early failure.

1.1.1 Start with the environment, not the wire

Before picking a gauge or jacket, write down where this harness lives and what it must endure.

1.1.1.1 Cable Harnesses in Industries

Automotive: In the automotive industry often referred to as the "nervous system" of a vehicle, the automotive cable harness is a critical and intricate component that plays a pivotal role in the functionality of modern cars. This complex assembly of wires, connectors, and other components is responsible for transmitting electrical power and data signals to nearly every part of the vehicle, such as; engine, lightnings, mirrors, transmission, battery-power cables etc.

As a quality management standard in the automotive industry there are many standards the industry follows such as; 

• IATF (International Automotive Task Force) 16949, This is the global technical specification and quality management standard for the automotive industry. Certification to IATF 16949 is a mandatory requirement for most vehicle manufacturers' suppliers.
• ISO 9001, it defines the requirements for a quality management system for organizations involved in the design, development, production, and, when relevant, installation and service of automotive-related products, including cable harnesses.
• VDA (Verband der Automobilindustrie). The German Association of the Automotive Industry, which develops standards and best practices, including the LV standards in collaboration with German automakers.
• Above all these standards, general cable harness requirements are in compliance with IPC standards (IPC/WHMA-A-620).

White Goods: A cable harness acts as the critical electrical distribution network within the white goods we rely on daily, such as washing machines, refrigerators, dishwashers, and ovens. This engineered assembly of wires, connectors, and other components is fundamental to their operation, safely transmitting power and control signals to every part of the appliance, from the main control board to the smallest sensor. As a quality management standard in the white good industry there are many standards the industry follows such as; 

• The IEC  (International Electrotechnical Commission) develops the foundational international standards for electrical and electronic technologies. For the white goods industry, the most critical series of standards is IEC 60335, which covers the "Safety of household and similar electrical appliances."

• UL (Underwriters Laboratories) For appliances sold in the North American market, compliance with UL and CSA standards is mandatory. These standards are highly focused on fire and electrical safety.

Defence Industry: Key standards like IPC/WHMA-A-620, alongstandard with a host of military specifications (MIL-STDs) for wires, connectors, and overall system design, formis the backbonemandatory ofquality producing robust and reliable cable harnessesbenchmark for the demandingcable environmentsand wire harness industry. It establishes the criteria for acceptance and rejection of all assemblies, ensuring consistency and reliability regardless of the defensemanufacturer. industry. 

1.1.1 Start with the environment, not the wire

Before picking gauge or jacket, write down whereUnderstanding this harness lives and what it must endure.

Capture (one page)

• Electrical: voltage (nom/max), current (avg/peak/inrush), allowed voltage drop, fault/short assumptions, return path, pin assignments.
• Mechanical: route length, fixed vs moving, bend radius, clamps/strain relief, pull loads, connector ingress/IP rating.
• Thermal & chemicals: min/max ambient, hot spots, oils/coolants/solvents, UV/outdoor, plenum/halogen-free needs.
• EMC: noisy neighbors (motors, DC/DC), victim lines (sensors, RF), shield bonding plan, separation rules.
• Regulatory/specs: customer standard, UL/IEC style, flame rating, label/traceability.

Decision gates

1. D1—Requirements frozen (the list above complete).
2. D2—Prelim sizing (gauge, insulation, shield picked; calcs pass).
3. D3—Route tryout (prototype in the product: bend/pull/EMC smoke test).
4. D4—Sign-off (BOM/spec + drawing released).

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1.1.2 Scaling & Measurement in Cable Harnesses Voltage, current & drop (the sizing triangle)

The primary scaling systems for wires in cable harnesses are the American Wire Gauge (AWG), the ISO 6722 metric system, and standards from the Society of Automotive Engineers (SAE). These systems are crucial for standardizing a wire's physical size and its electrical capacity.

1.1.2.1 American Wire Gauge (AWG)

The American Wire Gauge (sometimes called Brown and Sharpe or B. and S.) is used almost exclusively in the USA for copper and aluminum wire. The Birmingham Wire Gauge (BWG) is used for steel armor wire. The diameters according to the AWG are defined as follows: The diameter of size 4/0 (sometimes written 0000) equals 0.4600 inch and that of size #36 equals 0.0050 inch; the intermediate sizes are found by geometric progression.

• The AWG system is the most common standard in North America. It's an inverse, logarithmic scale, meaning:
• Smaller Gauge Number = Larger Wire: A 10 AWG wire is thicker and can carry more current than a 20 AWG wire.
• Logarithmic Scale: There's a fixed mathematical relationship between the gauge numbers. For every 6-gauge decrease, the wire's diameter doubles, and for every 3-gauge decrease, its cross-sectional area doubles.

The gauge number originates from the manufacturing process, representing the number of times a wire was drawn through a die to make it thinner.

AWG Size	Diameter (mm)	Cross-Sectional Area (mm²)	Resistance (Ω/km)	Ampacity (Chassis Wiring)	Common Application
4/0	11.68	107.2	0.16	~302 A	Main battery cables, high-power DC
2/0	9.27	67.4	0.26	~220 A	Large DC-DC converters, inverters
0 (1/0)	8.25	53.5	0.32	~195 A	High-current power distribution
2	6.54	33.6	0.51	~130 A	Amplifier power, starter motors
4	5.19	21.2	0.82	~94 A	Main power feeds, alternator cables
6	4.12	13.3	1.3	~73 A	Sub-system power feeds
8	3.26	8.37	2.1	~53 A	Medium-power devices, fuel pumps
10	2.59	5.26	3.3	~39 A	High-power speakers, lighting
12	2.05	3.31	5.2	~29 A	Standard power circuits, outlets
14	1.63	2.08	8.3	~22 A	General power and lighting
16	1.29	1.31	13.2	~17 A	Low-power devices, speakers
18	1.02	0.823	21	~13 A	General signal wires, sensor power
20	0.81	0.518	33.3	~9 A	Low-voltage signals, small sensors
22	0.64	0.326	53	~7 A	Data signals (CAN bus), LEDs
24	0.51	0.205	84.2	~5 A	Data communication, logic signals
26	0.4	0.129	133.9	~3.7 A	Internal wiring, ribbon cables
28	0.32	0.081	215.1	~2.2 A	Fine-pitch interconnects, sensors
30	0.25	0.051	341.8	~1.4 A	Very fine internal wiring, prototyping

1.1.2.2 ISO 6722 (Metric System)

The ISO 6722 standard is usedessential internationally, especially inbecause the automotiverequired industryworkmanship outsideand ofaudit Northrigor America.depend It'sentirely a more direct system that avoidson the counter-intuitiveProduct nature of AWG.

• ClassDirect Measurement: Wires are designated by theirthe cross-sectionalcustomer. area

  1.1.1 inThe squareAcceptance millimetersMandate: (mm²),Three Product Classes

  The IPC/WHMA-A-620 defines three classes based on the complexity, function, and consequence of failure. These classes dictate the acceptance criteria for defects such as 0.5 mm², 1.5 mm², or 2.5 mm².

• Clarity: A larger number directly corresponds to a larger, more capable wire. This simplicity is making it increasingly popular globally.

Nominal CSA (mm²)	Number of Strands	Conductor Diameter (mm)	Max. Electrical Resistance (Ω/km @ 20°C)	Common Application
0.35	7	~0.8	52	Low-voltage signals, sensors (LIN bus)
0.5	19	~1.0	37.1	General signals, lighting, CAN bus
0.75	19	~1.2	24.7	Low-power devices, control modules
1	19	~1.4	18.5	General power, small motors, lighting
1.5	19	~1.7	12.7	Standard power circuits, speakers
2.5	19	~2.2	7.6	Medium-power devices, outlets
4	56	~2.8	4.7	Power feeds, electric window motors
6	84	~3.4	3.1	Sub-system power feeds, amplifiers
10	80	~4.5	1.8	High-power feeds, starter motor solenoids
16	126	~5.7	1.2	Main power distribution, battery links

1.1.2.3 SAE (Society of Automotive Engineers)

The SAE has its own standards, like SAE J1128, for wires used in automotive applications.

Performance-Based: While it uses gauge numbers similar to AWG (e.g., 12 GA), SAE standards are primarily concerned with the wire's performance in a vehicle's specific environment.

• Not Always Interchangeable: An SAE gaugestripped wire maystrands, haveinsulation agaps, differentcrimp conductor size or stranding compared to an AWG wire of the same nominal gauge, so they are not always directly interchangeable.

SAE Gauge Size	Nominal CSA (mm²)	Min. Number of Strands	Max. Conductor Diameter (mm)	Max. Electrical Resistance (Ω/km @ 20°C)	Common Application
20	0.5	7	1.02	35.6	Low-voltage signals, sensors
18	0.8	16	1.27	22.3	General signals, lighting
16	1	19	1.47	17.6	Low-power devices, speakers
14	2	19	1.85	8.8	General power, small motors
12	3	19	2.34	5.5	Standard power circuits
10	5	19	3.12	3.5	Medium-power devices
8	8	19	4.29	2.2	Main power feeds, starter solenoids
6	13	37	5.38	1.4	High-power feeds, alternator cables
4	19	37	6.55	0.9	Main battery cables, high-current DC

 You need ampacity that’s safe, resistance low enough for drop,deformation, and insulationfinal that matches voltage.

Quick ampacity (free-air harness, short runs—derate for bundles/heat)

• 24 AWG ≈ 2 A; 22 AWG ≈ 3 A; 20 AWG ≈ 5 A; 18 AWG ≈ 7–10 A; 16 AWG ≈ 10–15 A.
  
   (Use your plant’s chart for final; these are starting points.)
  

Voltage drop check (DC or low-freq)

• Vdrop = I × Rtotal, where Rtotal = ρ(AWG) × (2 × length).
   Typical copper resistance per meter: 24 AWG ~0.085 Ω, 22 AWG ~0.053 Ω, 20 AWG ~0.033 Ω, 18 AWG ~0.021 Ω.
  

Worked example (step-by-step)

• 12 V motor, 3 A, 4 m one-way = 8 m round-trip.
• Try 22 AWG: Rtotal = 0.053 × 8 = 0.424 Ω. Vdrop = 3 × 0.424 = 1.272 V (≈ 10.6 % drop) → too high.
• Try 18 AWG: Rtotal = 0.021 × 8 = 0.168 Ω. Vdrop = 3 × 0.168 = 0.504 V (≈ 4.2 % drop) → acceptable.
  

Insulation rating

• Match or exceed system voltage and environment: common conductor temp classes 60/75/90/105/125/150 °C.
• For higher voltages, mind connector creepage/clearance, not just wire jacket.
  

Bundle derating

• Tightly tied, hot compartments, or conduit → size up or reduce allowable current. Post a simple plant rule (e.g., −20 % ampacity for dense bundles).
  

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1.1.3 Bend radius & motion class (don’t fight physics)

Pick static vs dynamic from the real use.routing.

CableIPC typeClass	StaticApplication min radiusRisk	DynamicReliability min radiusMandate	NotesManufacturing Mandate
Class 1	General PVCElectronic jacketProducts (Consumer, Disposable)	≥Functionality required for a short, specified life.6× OD	≥Focus on 10×maximum ODeconomy	Cold weatherand →basic increase 1.5×reliability.
Class 2	Dedicated ServiceShielded /(Industrial, multi-coreCommunications)	≥Extended service life where sustained performance is necessary, but failure is non-critical.10× OD	Standard Quality Baseline≥; requires measurable process controls (C15× OD	Shield & fillers need gentler bendspk).
High-flexClass (drag chain-rated)	≥ 7.5× OD3	7.5–10×High-Performance/Critical OD(Medical, Aerospace, Military)	Maximum ReliabilityUse; Classcontinuous, 5/6mission-critical fineperformance strand;where chainfailure layoutis testedunacceptable.	Most Stringent: Requires superior workmanship, maximum traceability, and near-zero defects.

1.1.2 Mandates for Critical Applications (Class 3)

GoodManufacturing practicea Class 3 harness is significantly more demanding than Class 2, requiring tighter controls across every stage of the assembly process.

A) Workmanship and Inspection

• Zero-Defect Philosophy:Add For critical attributes like crimp deformation, wire strand damage, and insulation gap, the acceptable tolerance window is minimized or eliminated. Any condition deemed "Acceptable" for Class 2 may be a service loopReject nearfor movingClass joints.3.
• Strain-reliefVisual bootsInspection: Requires higher magnification inspection and detailed logging of acceptance attributes.
• Destructive Testing: The frequency of mandatory destructive tests, such as the Terminal Pull Test and proper clamps beforeMicro-Section Analysis, theis firstoften bend.
• No 90° kinks; guide with saddles or grommets.
  increased.

B)

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1.1.4 Temperature, chemicals & jacket choice (survive the neighborhood)

Pick insulation/jacket for heat, cold, abrasion,Process and fluids.

Material

Exposure	Better materials	Why
Cold starts (≤ −20 °C)	TPE, PUR, CPE	Flexes in cold; PVC gets glassy
Hot zones (≥ 90 °C)	XLPE, FEP/PTFE, silicone	High temp class; stable dielectrics
Oils/coolants	PUR, CPE, TPU	Oil & abrasion resistant
Solvents/fuels	FEP/PTFE, XLPE	Broad chemical resistance
UV/outdoor	PUR, PE, UV-PVC	UV stable jackets
Tight space / plenum	LSZH, plenum-rated	Low smoke/halogen for building codes

Flame/halogen

• Match customer/building code: examples VW-1/FT-4 (UL/CSA), IEC 60332-1, LSZH where required.
  

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1.1.5 EMC: make quiet signals stay quiet

Layout & routing

• Separate power/switching from signals (rule of thumb: ≥ 100 mm; if you must cross, do it at 90°).
• Run along metal chassis and clamp at intervals (200–300 mm) to reduce loop area.
  

Twist & shield

Control

• TwistedTraceability: pairsClass 3 demands complete lot traceability for differentialevery signalscomponent in the harness (keepwire, twiststerminals, connectors, heat shrink). The MES system must be able to link the final harness serial number back to the terminal).raw material lot number.
• Shields:
• • FoilTool + drainCalibration: →All high-frequencycrimp electrictools, fields.wire strippers, and pull-test equipment must be under a strict calibration and maintenance schedule. The Crimp Height Measurement (CHM) must be logged and audited more frequently.
  • BraidCleanliness: →Requirements low-frequencyfor magneticcleanliness noise.(e.g., flux residue limits, use of gloves) are highly controlled, particularly for harnesses used in vacuum or harsh chemical environments.

  1.1.3 Acceptance Criteria: The GO / NO-GO Principle

  The IPC/WHMA-A-620 defines all acceptance criteria using three standard categories for any specific attribute (e.g., conductor deformation or strand damage):

  1. Acceptable: The condition is preferred and meets all design and performance requirements.
  2. ComboAcceptable, Target for Process Indicator: (foil+braid)The condition is acceptable but is considered a signal that the process may be drifting. Requires monitoring but is not yet a defect.
  3. Defect: The condition is unacceptable and violates the minimum performance requirement. The assembly must be rejected or reworked.

  The difference between Class 2 and Class 3 often determines whether a Target for broad-bandProcess pain.

Termination: aim for 360° shield bond with backshells; if pigtails are unavoidable, keep them <10 mm.

Bonding strategy

• Both-ends bondIndicator for EMIClass control2 whenbecomes noan DC/ground-loop issues.
• Single-end bond (one end to chassis) if DC currents/ground loops are a risk; addoutright common-mode chokes if needed.

Connector/pin tactics

• Interleave ground pins between fast signals.
• Keep return next to source (adjacent pins/pairs).
• Avoid starved grounds on high-di/dt loads; add extra grounds.
  

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1.1.6 Connector, strain relief & sealing

• Pick contact plating (Sn vs Au) to match mating cycles and current; size pin count so per-pin current stays relaxed.
• Use backshells that give 360° shield term where required.
• Seal to the environment: grommets, over-mold, or heat-shrink boots; meet target IP rating.
• Clamp cables before the connector to avoid load on contacts.
  

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1.1.7 Quick selector tables (get to 80% fast)

A) Choose conductor gauge by current & drop (short runs, free air)

• 0–2 A → 24–22 AWG
• 2–5 A → 22–20 AWG
• 5–10 A → 20–18 AWG
• 10–15 A → 18–16 AWG
  
   Then check Vdrop with the real length (1.1.2) and bump up if needed.

B) Pick insulation/jacket by environment

• Office/indoor benign → PVC or TPE, 60–90 °C.
• Machine bay with oil/drag chain → PUR, high-flex, 90 °C.
• Hot compartment → XLPE/FEP, 105–150 °C.
• Outdoor/UV → PUR/PE, UV-stable.
• Plenum/LSZH needed → LSZH jacket.

C) Bend class

• Fixed install → static rule.
• Door/hinge or robot → dynamic rule; pick high-flex cable.
  

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1.1.8 Validation (quick checks before you freeze the drawing)

• Route mockup with the real product: confirm clamp points, bend radii, and connector reach.
• Pull test at the first clamp (does the strain-relief work?).
• Heat soak at max ambient: watch jacket softening, contact temps.
• EMC sniff: scope common-mode on quiet pairs, try shield bond both vs one end.
• Continuity + flex cyclingDefect for movingClass harnesses (small shaker/drag chain rig).3.

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1.1.9Final CommonChecklist: trapsIPC →Class smallest reliable fixImplementation

TrapMandate	SymptomCriteria	FixVerification Action
Product Class Definition	SizedThe onlyrequired IPC Class (1, 2, or 3) is defined by ampacitythe customer contract and documented on the assembly drawing.	BigEnsures voltageall dropmanufacturing underprocedures, load	Dotooling, and inspection efforts are aligned to the Vdropcorrect math;risk upsize or shorten return pathlevel.
Traceability Mandate	PVCFull inlot cold/oilygenealogy baysis maintained for Class 3 projects.	Cracked,MES stiff,system oraudit swollenverifies jacketsthat	wire lot and terminal lotSwitch can be traced back to TPE/PUR;the raise temp classsupplier.
Tool Calibration	SharpAll 90°critical exitstermination tooling is under a strict Preventive Maintenance (PM) schedule.	EarlyCalibration conductorlogs break	Addprove grommet/boot;that increasecrimp radius;applicators repositionand clamppull-test machines are operating within spec.
Process Metrics	ShieldCpk pigtailsmonitoring longis implemented for critical processes (e.g., strip length and crimp height).	EMI fails	360° backshell or pigtails <10 mm; bond at both ends if allowed
Bundles packed tight	Overheat, crosstalk	Derate current; add spacers; split into two looms
Twists stripped early	Noisy sensors	Maintain pair twist toEnsures the contact;production pinprocess pairsmaintains adjacentlythe necessary statistical margin (≥1.33) required for Class 3 reliability.

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1.1.10 Pocket checklists

D1—Requirements

• Voltage/current/limits; drop target
• Route length, moving vs fixed, min radius
• Temp/Chem/UV; IP/flame/LSZH needs
• EMC sources/victims; shield/bond plan

D2—Sizing & selection

• Gauge passes ampacity + drop
• Bend class fits install; clamps placed
• Jacket/insulation match environment
• Shield type & termination defined

D3—Prototype tryout

• Fit/radius OK; no pinch points
• Pull + heat soak passed
• EMC quick test acceptable

D4—Release

• Spec table on drawing (gauge, jacket, temp, shield, radius)
• Connector pinout & plating; strain-relief details
• Labels/marking and test plan included

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Well-defined requirements and environment-driven design decisions transform cable harnesses from fragile assemblies into durable system lifelines. Freezing requirements early and validating them in real installations prevents costly rework and secures dependable operation across industries.