Buy a CAN harness against an approved network drawing that identifies each signal pair, its routing, every branch and the permitted end preparation. Correct pin-to-pin continuity is necessary, but it does not demonstrate that the physical pair arrangement and network topology match the design. A quotation saying “CAN cable, tested” leaves those questions open.
The useful purchasing package combines a connection table, a pair schedule, a dimensioned topology and an acceptance plan. Keep the cable manufacturer's construction evidence separate from the network designer's operating limits. Then require the assembly supplier to show how the delivered harness reproduces that agreed configuration.
This guide concerns the harness interfaces of high-speed differential CAN networks, including projects using CAN FD. It does not set a universal twist pitch, maximum untwist length or allowable stub. It also does not prescribe live testing or certify a network design. The engineering owner must approve the physical layer for the selected equipment, bit timing, installation and operating conditions.
Start with the network identity, not the cable nickname
Record whether the project uses Classical CAN, CAN FD or another explicitly identified implementation. Name the equipment interfaces and their applicable specifications. For CAN FD, request the configured arbitration and data-phase requirements rather than accepting one unqualified speed label.
CiA's CAN CC overview distinguishes the data link layer from physical medium access options and identifies high-speed CAN as one such physical layer. This distinction matters to procurement: a controller protocol designation does not completely specify the external harness.
Ask the engineering owner to identify the transceiver types or a controlled equipment interface specification that already incorporates them. The harness supplier may not need confidential board drawings, but it does need an authoritative boundary document. A product brochure advertising a maximum communication rate cannot replace approval of the actual connected network.
Also define the installation states that matter: normal equipment operation, an optional module fitted, a service adapter connected, or a branch deliberately unused. Treat these as named configurations. An assembly approved only for one configuration should not silently become the approved cable for every later accessory.
Add a pair schedule to the pinout table
A pinout table says where each conductor goes. A pair schedule says which two conductors must remain a physical pair between defined locations. These records answer different questions and should be reviewed together.
Assign a stable pair identifier, such as P-CAN1, with CAN_H and CAN_L as separate signal entries. Record the approved cable or paired-wire reference, conductor identifiers, endpoints and permitted interruption zones. If a harness contains two CAN networks, give each its own pair identifier and keep the networks distinct throughout the drawing.
Two conductors can reach the correct connector cavities while being taken from different physical pairs in a multi-pair cable. A basic continuity table may not reveal that construction error. Require the manufacturing drawing to preserve both the endpoint mapping and the pair grouping.
Use the existing pinout, cavity-view and wire-identification guide for connector orientation. Here, the additional control is the relationship between the two conductors along the route, including places where the jacket, sleeve or overmold later hides that relationship.
Consider a separate hypothetical pair-assignment check for two isolated networks, CAN1 and CAN2. The drawing requires physical pair A to carry CAN1_H and CAN1_L, and pair B to carry CAN2_H and CAN2_L. A proposed build instead groups CAN1_H with CAN2_H in pair A and both low signals in pair B, while still connecting every named signal to its correct connector cavity at both ends. That connection map can agree with the pinout while the physical pair schedule fails.
The appropriate disposition is to hold that build against the pair-schedule requirement, not to report a measured communication failure that has never been tested. Request a corrected construction record and the inspection evidence needed before the pair arrangement becomes hidden. This simple comparison makes the acceptance question specific without inventing a signal-integrity result or a universal cable limit.
Make the topology visible on one controlled drawing
Show the main bus, all branch junctions, every equipment connector and the intended termination locations. Identify the delivery boundary between the harness and the equipment. A neat bundle drawing that shows only external shape is insufficient when the electrical branch point is somewhere inside it.
Texas Instruments' SLLA270 application report, sections 4 and 4.8, explains the relationship between bus wiring, termination, propagation and reflections from unterminated stubs. It is a January 2008 report about the high-speed CAN context of that period; its example limits are not blanket CAN FD acceptance values.
For a purchasing drawing, define where each measured branch begins and ends. A dimension to the connector backshell is not automatically the complete electrical path to the transceiver. Have the equipment owner account for any additional internal wiring or board path in its network assessment.
Identify each junction by a reference that also appears in the splice or distribution-component drawing. Where the supplier delivers only one section, request the adjoining section's interface reference. This prevents each supplier from measuring a different fraction of the same branch and assuming the other fraction is negligible.
On small screens, swipe or scroll sideways to read every column. Keyboard users can focus the table and use the arrow keys.
| Controlled item | Required drawing entry | Useful evidence | Hold the quotation when |
|---|---|---|---|
| Signal pair | Pair ID and both conductor IDs | Cable construction and pair schedule | “Two wires” replaces a specified pair |
| Main route | Named endpoints and dimensional datums | Controlled harness drawing | Overall length has no measurement basis |
| Branch path | Junction, connector and equipment boundary | Complete topology reference | Only the visible breakout is dimensioned |
| End preparation | Defined untwist and exposed zones | Approved detail and inspection method | “As short as possible” is the only rule |
| Termination | Location, owner and configuration | Equipment or accessory specification | Every supplier assumes another installs it |
| Optional connection | Permitted accessory and state | Configuration approval record | A new service lead is treated as invisible |
Distinguish twist pitch, untwist and jacket removal
Twist pitch describes the axial distance associated with one full turn of the pair. Untwist length describes a region where the intended pair geometry is opened or separated. Jacket strip length describes removal of the outer covering. These dimensions can be different and must not share one ambiguous callout.
If the selected bulk cable already has a controlled pair construction, cite that exact cable and its applicable specification. Do not instruct an assembler to recreate its electrical properties merely by copying an apparent number of twists from a photograph. If production twists discrete wires, the design owner must define the approved construction and its verification basis.
Show the start and end datums for the untwist inspection. State whether the dimension follows the conductor path or a defined axial projection. Include the permitted assembly state during inspection: relaxed, fixtured or otherwise specified. Without this information, two inspectors can report different values on the same article.
Where a connector requires conductor separation for insertion, resolve the end geometry against its actual terminal and sealing arrangement before release. Do not demand a visually tighter twist if it conflicts with the approved assembly instruction. The decision belongs in a reviewed end detail, not in an operator's informal adjustment.
Control concealed preparation before closure
A final external photograph cannot establish pair condition inside an overmold or covered junction. Put the inspection point before the relevant feature becomes inaccessible, and identify the evidence that will accompany the first article.
For example, the purchase package can request a photographed preparation stage with the sample ID, pair ID, datum and measuring reference visible. It can also request the matching operation record for the subsequent closure. These are documentation choices, not claims that photography alone proves electrical performance.
Keep the accepted image linked to the drawing revision. A sample image from an earlier connector arrangement may remain useful background, but it should not be accepted as evidence for a changed exit geometry. If destructive examination is part of the project plan, agree its scope and sample disposition before ordering.
The objective is a repeatable process boundary: production knows what must be preserved, inspection knows when it can observe it, and purchasing knows which record closes the requirement. Avoid asking for a generic “internal quality checked” statement when the actual concern is one concealed separation zone.
Read the actual cable data rather than the marketing category
Compare the offered cable reference with the approved electrical and mechanical requirements. Preserve qualifiers such as nominal, maximum and typical, as well as the associated measurement conditions. A value without its qualifier can create a false pass.
Belden's 3105A product page provides a concrete documentation example: it lists one 22 AWG pair, nominal characteristic impedance of 120 ohms, and nominal conductor DC resistance of 18.2 ohms per 1,000 feet in separate fields. These are different properties; a resistance check does not substitute for the characteristic-impedance specification.
That example is not a recommendation of 3105A for every CAN installation or an assertion that SINAWATTS supplies it. Its product category and listed attributes help illustrate what information to request. The selected cable still requires approval for the actual environment, connector interfaces, routing and network.
Ask bidders to identify substitutions explicitly. Matching conductor size and jacket color does not establish matching pair construction. Compare the complete offered reference and supporting document against the baseline, and send unresolved electrical differences to the network owner before accepting a cost reduction.
Treat CAN FD and CAN SIC as configuration details
Do not transfer a length table from one network directly into another because both are called CAN. The useful RFQ question is which approved network assessment covers this exact topology and equipment set.
NXP's Reimagining CAN for Industrial discusses ringing in branched networks and contrasts conventional CAN FD transceivers with CAN signal improvement capability, or SIC, in a specified topology and simulation context. It supports checking the transceiver technology and topology together. It does not grant a universal branch-length allowance.
If the equipment changes to a different transceiver family, retain the original harness identity while the engineer evaluates the change. Conversely, do not assume an unchanged electronic unit approves a new branched harness merely because the cable carries the same signal names.
Record the conclusion as a configuration decision with the reviewed document references. A supplier statement that its cable is “CAN FD ready” may be a useful starting claim, but it needs a defined meaning and applicable evidence before it becomes an acceptance requirement.
Assign termination ownership and service-state responsibility
Specify who supplies each termination component or terminated accessory and where it belongs. Distinguish a component inside equipment from one built into a removable cable. Identify any switchable state and the controlling equipment instruction.
The purchasing risk is an ownership gap: the equipment supplier excludes external termination while the harness supplier assumes it is internal. The opposite problem is an unrequested additional termination included in an adapter. Both require an accurate configuration list rather than a generic instruction to include resistors.
For every detachable branch or service lead, ask what happens to the approved topology when it is connected or removed. Have the network owner define permitted service states. A dust cap should not be described as an electrical termination unless the exact item and evidence establish that function.
Keep spare assemblies and service accessories in the same configuration register as production harnesses. A replacement cable that physically fits but changes the termination arrangement should require a documented review, even when its pin-to-pin mapping appears identical.
Compare evidence at cable, assembly and equipment level
Use three separate evidence levels. Cable evidence identifies construction and specified properties. Assembly evidence shows the approved cable was processed into the required harness. Equipment evidence establishes that the complete network meets its operating requirements in the represented configuration.
A communication demonstration on a short bench setup may help identify an obvious error. It does not automatically cover the installed routing, all nodes, optional branches or operating conditions. Request the configuration record and the scope of the result rather than accepting an isolated “communication passed” label.
Similarly, a continuity test can confirm the tested connection map while leaving pair grouping and hidden preparation unexamined. Build an inspection matrix that names the requirement and the evidence that addresses it.
On small screens, swipe or scroll sideways to read every column. Keyboard users can focus the table and use the arrow keys.
| Evidence level | What it can support | What remains outside that evidence |
|---|---|---|
| Exact cable data | Defined construction and listed characteristics | Finished breakout geometry |
| Pair and preparation inspection | Agreement with specified physical arrangement | Complete network timing margin |
| Connection-map test | Tested connectivity and specified isolation | Installed communication suitability |
| Approved network assessment | Suitability of represented configuration | Unreviewed cable or equipment changes |
| First-article package | Traceability of the approved sample | Unlimited future substitution permission |
Use the harness electrical-test guide to keep inspection purposes distinct. Agree any specialist signal-integrity or communication verification with the responsible engineer; do not improvise test voltages or acceptance limits from this article.
Send the network drawing, pair schedule and unresolved interface questions for a harness RFQ.
Worked example: compare three branch-harness offers
The following example is hypothetical. Its dimensions, identifiers and limits are invented solely to demonstrate document review. They are not universal CAN limits, measured results, customer cases or SINAWATTS product specifications.
Assume the project engineer has already approved network configuration N-24 revision D for the named equipment. Its purchasing interface allocates a maximum 0.50 m electrical branch path from junction J1 to the transceiver boundary. The equipment drawing assigns 0.06 m maximum to the internal path. Harness drawing H-24 requires the external branch to be no more than 0.40 m, leaving 0.04 m unallocated margin in this simplified dimensional check.
The same hypothetical drawing requires pair P-CAN1 to remain associated through the branch and specifies no more than 25 mm of conductor separation at one named connector detail, measured between its defined datums. It also prohibits an additional termination inside the delivered harness.
On small screens, swipe or scroll sideways to read every column. Keyboard users can focus the table and use the arrow keys.
| Offer | Declared external branch | Preparation and topology evidence | Procurement disposition |
|---|---|---|---|
| A | 0.38 m with +0.02 m tolerance | Correct pair, 20 mm maximum separation, no added termination | Dimensional and document screen passes; verify the first article |
| B | 0.46 m with +0.02 m tolerance | Correct pinout; other details match | Hold: maximum total path is 0.54 m |
| C | 0.38 m with +0.02 m tolerance | Pair detail absent; termination added without approval | Hold despite acceptable branch dimension |
For offer A, the maximum external path is 0.40 m. Adding the specified 0.06 m internal allowance gives 0.46 m, which is below the assumed 0.50 m allocation. This arithmetic supports only the stated dimensional screen. It does not independently prove waveform quality, EMC performance or network reliability.
Offer B reaches 0.48 m externally and 0.54 m with the equipment allowance. Do not compare its nominal external value alone with the full-path limit. Ask for a corrected branch or a formal engineering reassessment; purchasing cannot waive the mismatch because a sample happens to communicate.
Offer C illustrates a separate decision. Its length fits, but the missing pair detail and additional termination leave the approved configuration unproven. Return those differences for resolution rather than combining all three offers into a price-only ranking.
Before ordering A, confirm that the quoted cable reference, connector preparation and equipment revision are exactly those represented by the approved configuration. The example starts with that engineering approval; it does not explain how to create it or suggest that the invented limits would suit another network.
Build a first-article checklist from the drawing
For each critical requirement, provide its drawing reference, acceptance basis, inspection stage and record location. Keep the checklist specific enough that an inspector can distinguish a completed check from a generic signature.
Begin with assembly and cable identity. Continue with pair assignments, junction locations, connector orientation and dimensions. Then inspect the end-preparation features at the stage when they remain accessible. Finally, verify the delivered termination configuration and the controlled connection map.
Request records for actual measured values where the plan requires measurement, rather than a pass mark beside every dimensional requirement. The accepted method must account for tolerances and the defined measurement state. If a feature cannot be measured reliably in the proposed process, resolve the method before production approval.
Use the length, datums and breakout-tolerance guide for the general dimensioning framework. For this CAN harness, add the electrical-path boundary and pair geometry so the physical inspection remains linked to the network requirement.
Keep shield decisions separate from signal-pair decisions
A shield arrangement and a twisted-pair arrangement are related parts of the assembly, but they are not interchangeable specifications. A complete shield path does not prove that CAN_H and CAN_L remain the intended pair. Equally, a correctly paired cable does not settle the equipment's shield connection.
Reference the approved shield drawing separately and preserve its intended connections and isolations. Do not use a drain wire as an unnamed substitute for a signal conductor or reference connection. If the network interface includes additional reference conductors, identify them explicitly in the interface document.
The end-to-end shield termination guide covers drain wires, connector shells and circumferential interfaces. This article instead controls signal-pair association, branch geometry and network evidence. Review both records where the project uses a shielded CAN cable, without assuming that one approval covers the other.
Manage changes without repeating unnecessary qualification
Create a concise change-impact list for the approved harness. Include cable reference, pair construction, connector or contact arrangement, end preparation, junction location, branch length, termination content and service accessories. These features are candidates for engineering review when changed.
Not every change requires the same work. A label wording correction may need document reconciliation, while a longer branch or different cable construction can require a new network assessment. Ask the responsible engineer to record the required verification scope and its reasoning.
Keep the earlier approval and record the change against it rather than erasing the original configuration. For supplier transfers, request evidence that the new manufacturing process reproduces the approved preparation and junction details. A drawing shared between factories does not establish that hidden assembly operations are identical.
This approach also helps purchasing compare lead time honestly. Request separate estimates for drawing review, sample preparation, inspection and any equipment-level evaluation. Do not promise a fixed production date until the required evidence and responsibilities are agreed.
FAQ
Is a correct CAN pinout enough to approve a harness?
No. The pinout addresses signal endpoints. The purchase package should also control physical pair association, branch paths, end preparation and termination content. A correctly wired sample can still differ from the configuration evaluated by the network designer.
What maximum untwist length should the RFQ specify?
Use the limit and measurement method approved for the actual cable, connector and network. This guide does not provide a universal value. If no limit exists, request an engineering decision before releasing the preparation drawing; “minimum possible” is not a repeatable inspection criterion.
Can a generic twisted pair replace a specified CAN cable?
Only after the proposed construction and evidence have been reviewed against the project requirements. Conductor size and a twisted appearance do not establish equivalent electrical or environmental properties. Ask for the exact substitute reference and a marked comparison, with approval retained in the configuration record.
Does CAN FD always require the same branch-length limit?
No. The applicable assessment depends on the represented topology, equipment and operating configuration. CAN FD or SIC terminology alone does not supply an approved limit. Preserve the engineer's full-path definition and do not borrow a value from an unrelated demonstration.
Does shield continuity prove the signal pair is acceptable?
No. Shield connectivity and signal-pair geometry address different requirements. Review the shield record separately from the pair schedule, and link each inspection result to its actual purpose. Neither result alone proves complete equipment communication performance.
What should a supplier include with a first-article quotation?
Request a marked drawing, exact cable and connector references, pair schedule, preparation details, branch tolerances and proposed inspection records. Identify any assumptions about equipment paths or termination. List specialist verification separately so its cost, owner and scope are visible.
Which information is needed before price and lead time can be confirmed?
Provide quantities, the controlled assembly drawing, approved cable alternatives, connector references and acceptance scope. Explain whether network approval is complete or still pending. Ask the supplier to distinguish confirmed manufacturing scope from unresolved engineering work; this article does not state SINAWATTS pricing, availability or delivery commitments.
Prepare a CAN harness inquiry that can be evaluated
Start with the OEM and ODM project page, then attach the network interface document and assembly requirements. Explain whether the inquiry concerns a repeat build, a supplier transfer or a proposed topology change. These situations need different evidence even when the requested cable looks similar.
The most useful submission has one consistent configuration: named equipment, approved cable, pair schedule, dimensioned branches, end details, termination ownership and acceptance responsibilities. Highlight unresolved requirements openly so they can be addressed before sample or production release.
Send your CAN topology, pair schedule and harness drawing for a project RFQ.