1.4 Shielding & Protection
19.3.1 Cable Harness Drawing Rules
Wire harness drawing standards are guidelines and specifications that define how wire harness drawings should be created and formatted. These standards ensure consistency, clarity, and accuracy in wire harness documentation, making it easier for designers, manufacturers, and technicians to understand and work with the harnesses.
While specific standards can vary based on industry and application, here are some common elements found in wire harness drawing standards:
- Title Block
- Scale
- Drawing Views
- Symbol Library
- Wiring Diagrams
- Wire Routing
- Connector Information
- Wire Identification
- Bill of Materials (BOM)
- Revision Control
19.3.1.1 Title Block
A title block is typically placed at the bottom right corner of the drawing and contains essential information such as the drawing title, revision number, date, part number, and the name of the drafter.
Key Information Found in a Title Block
The title block is divided into several smaller sections, each containing specific metadata:
- Part Name / Title: A clear, descriptive name of the assembly (e.g., "HARNESS ASSEMBLY, MAIN ENGINE").
- Drawing Number: The unique number that identifies the drawing. For a harness, this is almost always the same as the Part Number of the assembly itself.
- Revision Level: A critical field that indicates the version of the drawing (e.g., A, B, C, or 1, 2, 3). Manufacturers must always work from the latest approved revision to avoid building an obsolete part.
- Approval Block: This section contains the names or initials of the individuals who created, checked, and approved the drawing, along with the dates. This establishes accountability and a traceable record of the design process. Common fields include:
- DRAWN BY
- CHECKED BY
- ENG. APPROVAL
- MFG. APPROVAL
- Company Information: The name and address of the company that owns the design.
- Tolerances: A block that defines the default dimensional tolerances for any measurements on the drawing that do not have a specific tolerance called out (e.g., "UNLESS OTHERWISE SPECIFIED, TOLERANCES ARE: X.XX = ±0.50").
- Scale: The ratio of the size of the items on the drawing to their actual size (e.g., 1:1, 1:2). For large harnesses, this is often listed as "NTS" (Not To Scale).
- Sheet Information: The size of the drawing sheet (e.g., A, B, C, or A4, A3) and the sheet number if the drawing package contains multiple pages (e.g., "SHEET 1 OF 3").
19.3.1.2 Drawing Views
Wire harness drawings usually include multiple views, such as plan views, elevation views, and section views, connector View orientation to provide a comprehensive representation of the harness layout. Especially the connector's view direction, you know, from the top or from the back view have different circuits, we have the traumatic experience of viewing it wrong, then making a whole order wrong.
- The graphical representation is the core of the drawing.
- Clear, Scaled View: The main drawing should show the harness laid out flat in a 1:1 scale if possible, or a clearly noted smaller scale. All branches, connectors, and components should be shown in their correct geometric relationship to each other.
- Dimensioning: Every critical dimension must be included. This includes the overall length, the length of each branch from its breakout point, and the locations of any labels or hardware. Tolerances are essential for all lengths.
- Connector Orientation: The "clocking" or orientation of connectors (especially angled or keyed ones) must be clearly defined in a separate detail view to ensure they are installed correctly.
19.3.1.3 Symbol Library
- A standardized library of symbols is used to represent various components, connectors, terminals, splices, and other elements within the wire harness.
19.3.1.4 Wiring Diagrams
Wiring diagrams show the electrical connections between components, including wire routing, branching, and termination points. These diagrams often use standardized symbols and color codes to represent different wires, connectors, and functions.
19.3.1.5 Wiring Routing
The routing of wires within the harness should be clearly illustrated, indicating the path, bundling, and securing methods. This includes any clips, ties, or sleeves used to manage and protect the wires.
19.3.1.6 Standards and Requirements Table
The standards and requirements on a cable harness drawing are a set of notes that define the quality, testing, and manufacturing criteria for the assembly. These are typically located in a "General Notes" section on the drawing and serve as a formal instruction set for the manufacturer, ensuring the harness meets all technical and performance specifications.
19.3.1.7 BOM List
The BOM is a structured list of every component required to build one unit of the harness assembly. It serves as the primary document for procurement and inventory control. A comprehensive BOM must include:
- Item Number: A unique sequential identifier for each line item.
- Part Number: The specific manufacturer or internal part number for the component.
- Description: A concise technical description (e.g., "CONN, RCPT, 12 POS, DTM SERIES").
- Quantity: The total quantity of the component required per single harness assembly.
- Reference Designator: A unique identifier (e.g., P1, J2, W3) that links the component in the BOM to its location on the graphical drawing.
19.3.2 Specification Documentation
Cable harness specification documentation is the complete set of technical documents that formally defines all the requirements needed to manufacture, inspect, and test a cable harness. This package serves as the single source of truth and the contractual agreement between the design authority and the manufacturer.
Its purpose is to provide a clear, unambiguous, and comprehensive set of instructions that ensures every harness is built to the exact same standard.
These are separate documents that are referenced on the main drawing. They provide detailed instructions on how to perform specific tasks.
- Workmanship Standard: This is almost always IPC/WHMA-A-620. The drawing will specify the required class (e.g., Class 2 or Class 3).
- Crimp Specifications: For critical applications, there may be a separate document detailing the exact tooling, crimp heights, and pull-force requirements for each terminal.
- Test Procedures: A detailed procedure that outlines the steps for electrical testing, including the specific equipment to be used, the test voltage (for Hipot), and the pass/fail criteria.
19.3.2.1 Quantities
One of the important criteria for cable harness calculation and production is quantities.
In cable harness manufacturing, quantities are a fundamental input for all technical and logistical calculations. They directly influence cost, production strategy, and quality control. The two primary types of quantities are the per-harness quantity (defined by the Bill of Materials) and the total production quantity (the number of harnesses to be built).
The accuracy of a price quote is directly dependent on precise quantity calculations.
Bill of Materials (BOM) Cost Roll-up: Component pricing is heavily dependent on volume. A harness built in quantities of 100 will have a significantly higher per-unit material cost than one built in quantities of 10,000 due to price breaks from suppliers. Calculations must use the price points corresponding to the planned production volume.
Economies of Scale: Component suppliers offer tiered pricing. The total production quantity determines which price break the manufacturer can achieve. For example, the unit price for 10,000 terminals is significantly lower than for 1,000. A larger production volume allows for more aggressive material pricing.
Amortization of NRE Costs: Non-Recurring Engineering (NRE) costs include the design of the harness, creation of the manufacturing formboard, and programming of test equipment or any machine equipment investment. These are fixed, one-time costs. The total production quantity is used to amortize these costs, spreading them across all units.
Per-Unit NRE Cost = Total NRE Cost / Total Production Quantity A larger quantity dramatically reduces the per-unit NRE cost.
19.3.2.2 Quantities Effects on Capacity Planning
The production quantity is the central input for capacity planning, which involves allocating the necessary resources (machines, labor, space) to meet production targets.
- Machine Hours: The total quantity determines the required machine hours. For example, a run of 10,000 harnesses with 20 crimps each requires 200,000 machine cycles. The capacity planner must calculate if the available crimping presses can perform this work within the scheduled timeframe or if additional machines or shifts are needed.
- Labor Allocation: The total labor hours are calculated by multiplying the per-unit assembly time by the quantity. The planner uses this to determine the required number of assembly technicians and to schedule their work.
- Assembly Stations: The quantity and complexity of the harness dictate the number of physical assembly boards or stations required on the production floor to meet the delivery schedule without creating bottlenecks.
- Future Resource Planning: Long-term quantity forecasts are used to make strategic decisions. If a forecast shows a sustained high volume for a new project, the company may decide to invest in new automated equipment, expand the factory floor, or hire and train more staff in anticipation of the increased workload.
In this case, specifically processes evaluated as a total amount of cable harnesses and process timing to find possible machine investment decisions. It defines the usage percentage of machines.
In this case, processes calculated by the total amount of cable harnesses equal to an hour. Capacity study starting with process timing, machine capacity validation, customer transport forecast.
Braids, foils, drain wires, sleeves, and routing for noise/abrasion control.
Shielding and protection give a harness two kinds of defense—against electrical noise and against the physical abuse of heat, motion, and abrasion. Foils, braids, and combination shields each have strengths for different frequency ranges and flexibility needs, while sleeves, overbraids, and armor keep insulation intact over years of service. The most effective designs terminate shields with a full 360° bond at the entry point, minimize exposed pigtails, and route cables close to chassis metal to shrink loop areas. Smart choices in clamps, grommets, and branch protection prevent mechanical wear from undoing electrical performance. When shielding and protection are planned together, the result is a harness that stays both electrically quiet and physically durable in its working environment.
19.34.1 Why shield & protect (two jobs, one harness)
- EMC job: keep noisy stuff in, keep sensitive stuff quiet. That’s about impedance to ground and small loop areas.
- Mechanical job: survive rubs, edges, heat, and motion without nicking insulation or the shield itself.
Design both at once—an elegant shield that frays on the first bracket is still a failure.
19.4.2 Picking the shield (what each does best)
Rule: Signals near switchers or long harnesses → combo. Short sensor runs in quiet boxes → foil + drain often suffices.
19.4.3 Termination that works (and what to avoid)
Gold standard: 360° bond of the shield to a metal backshell or clamp—no gaps, no whiskers.
- Backshells with spring fingers/cones give true 360°.
- Band clamps or dedicated EMI glands do similar at bulkheads.
Pigtails (if you must):
- Keep total exposed length ≤10 mm.
- Use drain wire for foil shields; braid pigtails are last resort.
- Bond as close as physically possible to the chassis entry.
Bonding strategy:
- Both-ends bond when possible (best EMI).
- If ground loops/DC offsets are a risk: bond at one end and add AC path (e.g., 1–10 nF to chassis or a common-mode choke on the pair) to keep RF currents off the conductors.
Checklist at drawing time: call out “360° shield termination at Jx backshell” or “Drain to chassis, pigtail ≤10 mm @ Jx.”
19.4.4 Drain wires (foil’s best friend)
- Must touch foil continuously—factory-applied under the foil is ideal.
- Terminate the drain with the shield (not to signal ground pins unless specified).
- If you splice, cap and insulate the drain at the splice; don’t leave “antennas.”
19.4.5 Sleeves, jackets & armor (save the insulation)
Edges & pass-throughs: always use grommets/bushings and edge guards. No bare metal on insulation—ever.
19.4.6 Routing rules that buy dB (and years)
- Separate power/switching from low-level signals by ≥100 mm; if they must cross, do it at 90°.
- Hug chassis metal and clamp every 200–300 mm to shrink loop area.
- Avoid parallel runs with antennas/RF; keep to one side of high-di/dt cables.
- Put the bond point at the entry to the metal enclosure (don’t carry “RF” inside).
- First bend after strain relief, not at the backshell.
19.4.7 Clamps, strain relief & branch points
- Use cushioned P-clamps; size so rubber compresses slightly.
- Place the first clamp before the first bend and within 50–80 mm of the backshell.
- Branches: reinforce with heat-shrink boots or molded splitters; no zip-tie cuts—use lacing tape or rounded ties over sleeves.
19.4.8 Validating shielding & protection (quick but honest)
- Continuity to chassis: < 0.05–0.10 Ω from backshell to chassis; verify both ends if bonded.
- Transfer sanity check: near-field probe the noisy board, compare with/without shield bond; aim for a clearly lower trace.
- Flex/abrasion test: cycle through expected bend radius; inspect sleeves and any braid for broken filaments or jacket scuff.
- Ingress check (sealed families): IP test or at least soapy water spray + pressure decay on suspect connectors.
- Pull test at clamp: the clamp should take load—not the pins.
19.4.9 Common traps → smallest reliable fix
19.4.10 Pocket checklists
At design freeze
- Shield type chosen (foil/braid/combo) per noise & flex
- Termination called (360° backshell vs pigtail ≤10 mm)
- Bond strategy (both ends or single + AC path) noted
- Sleeve/armor picked for environment; grommets specified
- Clamp spacing & first-clamp distance on drawing
During build
- Shield strands tidy; no whiskers; boots shrunk clean
- Drain tied only to the intended bond point
- Labels outside clamps; no ties over bare insulation
- Bend radius respected at exits/branches
Verification
- Chassis bond resistance measured & logged
- Quick probe/EMI sniff improved with bond on
- Flex/abrasion spot check OK; no jacket cuts at edges
Bottom line: pick a shield for the spectrum you’re fighting, bond it 360° at the right place, keep loop areas small with smart routing, and dress the harness with sleeves, boots, and clamps so it survives real life. Do that, and you’ll get a cable that’s both quiet and tough—exactly what the product needs.