A harness can match its quoted overall length and still put a branch in the wrong place. Before comparing prices, define what each dimension measures, where it starts and ends, and which tolerance applies. Require the supplier's drawing and inspection record to use those same definitions.
This guide focuses on finished dimensions and breakout locations. Use the custom cable assembly RFQ checklist for the wider electrical, material and commercial specification. Correct length does not establish correct wiring, movement capability or equipment suitability.
Define the measurement before the number
A datum here means an explicitly identified measurement reference on the drawing. It might be a connector back face, terminal-hole center or defined junction feature. These are alternatives to identify, not interchangeable ways to measure one nominal length.
Separate conductor cut length, finished assembly length and installed route length. Wire consumed inside a termination or housing must not disappear into an unstated assumption. Ask the supplier to identify which finished dimension its cutting and assembly process is intended to achieve.
Molex's 2019 cable assembly design guide recommends using connector back faces as length references where possible. This is useful design guidance for the assemblies discussed there, not a universal rule overriding a project's approved drawing. Molex Cable Assembly Design Guide, page 18.
Label both ends of each dimension. Specify whether it follows the cable path or measures a direct distance between features. A route around an obstacle and the straight distance across it are different quantities. Add units and a detail view when a connector, boot or sleeve could conceal the intended reference.
Keep connector orientation tied to the same references used in the harness pinout drawing guide. Changing a viewing direction does not authorize changing the measurement endpoint.
Make the measurement state repeatable
Agree whether the assembly is measured laid out, in a defined fixture or in its installed route. Record how connectors are located, how branches are arranged and which supports or accessories are fitted. Identify any specified conditioning or measuring force; do not let an inspector pull an assembly until it reaches the nominal number.
The buyer's drawing should distinguish a service loop from dimensional tolerance. A loop is an intentional route feature; tolerance is the permitted variation in a defined dimension. Do not remove the loop during inspection unless the agreed measurement method requires that configuration.
For moving installations, review the separate strain relief and bend radius guide. A dimensional inspection alone does not verify freedom from tension, acceptable bending or repeated-motion life.
Give each breakout its own controlled definition
Name every junction, branch and connector. Define the breakout reference with a detail that both parties can locate consistently. The visible edge of tape, the end of a protective boot and the point where conductors diverge may describe different features; do not silently substitute one for another.
Samtec's IDSS/IDSD/IDMS/IDMD catalogue separately identifies assembled length, breakout and daisy-chain options, with their own dimensional information. It illustrates why “cable length” alone does not describe all configurable features. Its ribbon-cable conventions and limits apply to those series, not every branched harness. Samtec IDC cable catalogue, page 2.
Use a dimension schedule such as this original RFQ checklist:
On small screens, swipe or scroll sideways to read every column. Keyboard users can focus the table and use the arrow keys.
| Drawing field | Definition to agree | Hold if missing |
|---|---|---|
| Main length | Named start/end references and measurement path | “Overall” has no defined endpoints |
| Junction location | Identified datum and repeatable locating detail | Tape edge and junction location are confused |
| Branch length | Junction reference to named connector feature | Branch measured from an unspecified point |
| Connector position | Orientation and accessory state during measurement | Different connector positions change the result |
| Permitted range | Nominal value, lower limit and upper limit | A tolerance has no sign, unit or scope |
| Inspection method | Assembly state, fixture and reporting rules | Buyer and supplier measure differently |
Read the applicable tolerance, not just the title block
Molex's design guide presents recommended tolerances for both overall and branch lengths and discusses the cost effect of tighter requirements. Those recommendations are a manufacturer's design starting point. They do not establish an industry-wide default or a confirmed capability for a SINAWATTS quotation. Molex guide, pages 7 and 18.
A product-specific drawing can use a different scheme. Molex drawing 1203410890, revision A8 dated 21 March 2024, has a dedicated cable-length tolerance table as well as a general decimal-dimension block. Its length table uses positive tolerance entries. The procurement lesson is to read the specific length callout and applicable table, rather than borrowing the title-block value. Molex cable assembly drawing, sheets 1–2.
Ask each bidder to return explicit minimum and maximum finished dimensions. Resolve whether the limits are bilateral, one-sided or individually stated. Have the responsible engineer approve any deviation; a wider range can change fit even when the nominal value remains identical.
Worked comparison: the same total can hide a misplaced junction
This is a fictional drawing-review exercise, not a customer case, production result or recommended tolerance. In harness H-032 revision B, A and B are defined connector back-face references. S is a junction datum located by an agreed detail and fixture. The main path comprises two contiguous measured segments through S; a third segment leads to connector P3.
On small screens, swipe or scroll sideways to read every column. Keyboard users can focus the table and use the arrow keys.
| Controlled dimension | Requirement in this example | Permitted interval |
|---|---|---|
| A to S | 540 ±6 mm | 534–546 mm |
| S to B | 360 ±8 mm | 352–368 mm |
| S to P3 reference face | 180 ±5 mm | 175–185 mm |
The nominal sum along the main path is 900 mm. The drawing marks that sum as reference information; the segment limits control acceptance. This avoids adding an unexplained, independently toleranced total to the same chain.
Reply A quotes only “900 ±20 mm overall.” Hold dimensional approval: it neither accepts the segment limits nor establishes the junction and branch locations. Request a completed schedule.
Reply B reports 552 mm from A to S and 348 mm from S to B. Its total is exactly 900 mm, yet the first segment exceeds 546 mm and the second falls below 352 mm. Reject those dimensions against this drawing revision; a correct sum does not cancel either failure.
Reply C reports 538, 364 and 182 mm against the three controlled dimensions, using the agreed references and method. Each lies within its stated interval. The main-path sum is 902 mm, which does not conflict with the 900 mm reference value. Accept only this dimensional comparison, subject to the agreed inspection decision rules and valid records; other release requirements remain separate.
This addition works because the two segments share S and follow the same defined main path. Do not add unrelated straight-line distances or silently apply this arithmetic to a differently routed three-dimensional assembly.
Connect inspection evidence to the accepted drawing
Request a dimensional report that identifies the assembly, drawing revision, inspected quantity, date, method and measuring equipment. Each controlled dimension should have a stable identifier, specified limits, actual result and disposition. Agree how measurement uncertainty and borderline results will be handled before deciding acceptance.
A fixture photograph is helpful only when it identifies the locating features and corresponds to the agreed method. Ask how the fixture revision is maintained and how its suitability is checked. Do not treat a photograph beside a ruler as complete evidence for a junction hidden under sleeving.
Keep an unresolved dimension open until the named reviewer accepts a correction or documented deviation. Require change notification when a different connector, boot, sleeve or assembly route changes a reference or the resulting finished dimensions. The first-article and change-control guide covers the broader release record.
Send a dimensioned harness RFQ
Attach the drawing revision, datum details, dimension schedule, measurement state, quantities and sample requirements. Ask bidders to separate production price from any fixture, documentation or additional inspection work, and identify the approval milestones affecting delivery. No price or delivery assumption should conceal an unresolved dimensional deviation.
Buyer FAQ
Is nominal cable length enough for a replacement harness?
No. Identify the finished endpoints, measurement path, breakout locations and accepted ranges. A matching nominal number measured from different features does not establish dimensional equivalence.
Should every dimension have the tightest possible tolerance?
Have engineering identify the dimensions that control fit and function, then obtain a feasible proposal. Unnecessarily tight limits can add work; an unsupported loose limit can prevent fit. Resolve the actual requirement before comparing costs.
Can an overall measurement replace branch inspection?
Only if the approved requirements explicitly make the other dimensions unnecessary. In a branched harness, a passing total generally leaves the junction and individual branch dimensions unverified.
Does one approved sample establish production consistency?
It establishes only what was checked on that sample. Agree the production inspection scope, traceability, decision rules and change controls separately, with any associated commercial terms.