1.1 Requirements & Environments
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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, along with a host of military specifications (MIL-STDs) for wires, connectors, and overall system design, form the backbone of producing robust and reliable cable harnesses for the demanding environments of the defense industry.
1.1.1 Start with the environment, not the wire
Before picking gauge or jacket, write down where 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
- D1—Requirements frozen (the list above complete).
- D2—Prelim sizing (gauge, insulation, shield picked; calcs pass).
- D3—Route tryout (prototype in the product: bend/pull/EMC smoke test).
- D4—Sign-off (BOM/spec + drawing released).
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.
1.1.2.2 ISO 6722 (Metric System)
The ISO 6722 standard is used internationally, especially in the automotive industry outside of North America. It's a more direct system that avoids the counter-intuitive nature of AWG.
- Direct Measurement: Wires are designated by their cross-sectional area in square millimeters (mm²), 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.
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 gauge wire may have a different conductor size or stranding compared to an AWG wire of the same nominal gauge, so they are not always directly interchangeable.
You need ampacity that’s safe, resistance low enough for drop, and insulation 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).
1.1.3 Bend radius & motion class (don’t fight physics)
Pick static vs dynamic from the real use.
Good practice
- Add a service loop near moving joints.
- Strain-relief boots and proper clamps before the first bend.
- No 90° kinks; guide with saddles or grommets.
1.1.4 Temperature, chemicals & jacket choice (survive the neighborhood)
Pick insulation/jacket for heat, cold, abrasion, and fluids.
Flame/halogen
- Match customer/building code: examples VW-1/FT-4 (UL/CSA), IEC 60332-1, LSZH where required.
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
- Twisted pairs for differential signals (keep twists to the terminal).
- Shields:
- Foil + drain → high-frequency electric fields.
- Braid → low-frequency magnetic noise.
- Combo (foil+braid) for broad-band pain.
- Termination: aim for 360° shield bond with backshells; if pigtails are unavoidable, keep them <10 mm.
Bonding strategy
- Both-ends bond for EMI control when no DC/ground-loop issues.
- Single-end bond (one end to chassis) if DC currents/ground loops are a risk; add 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.
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.
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.
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 cycling for moving harnesses (small shaker/drag chain rig).
1.1.9 Common traps → smallest reliable fix
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