A cable assembly can have the correct length and connectors yet leave a purchasing question unresolved: what supports the cable when a cabinet door opens, a battery tray moves or an operator handles the lead?
Ask for a routing drawing, the exact cable's movement limits and the proposed strain relief arrangement together. A minimum bend radius for fixed installation does not establish suitability for repeated movement. This guide turns that distinction into quotation and sample-approval questions.
Use the custom cable assembly RFQ checklist for the wider electrical and commercial specification. Here, the decision is about the mechanical route and its supporting evidence.
Separate support, bending and movement
Strain relief provides a path for external cable loads into a supporting structure. igus describes this function as protecting connections by transferring forces to the structure carrying the restraint. Its explanation supports checking the complete mounting arrangement, rather than judging a clamp by appearance alone. igus strain relief principles.
Bend radius describes the curvature allowed under stated conditions. Keep the manufacturer's measurement convention on the drawing; a radius, a loop diameter and a clearance dimension are different measurements.
Movement duty describes what happens during use. Distinguish a lead formed during installation, a service loop repositioned occasionally and a cable flexing on every machine cycle. Record twisting separately from bending. A label such as “flexible cable” leaves these questions unanswered.
Mark the connector exit, first restraint, moving segment and any surface the cable could contact. Ask the designer to show where the load is intended to go and which section is intended to move.
Why there is no universal minimum bend radius
LAPP's published data for ÖLFLEX CLASSIC 110 BK distinguishes fixed installation, occasional movement and power-chain use. The listed radii are respectively 4, 10 and 15 times the cable's outer diameter, with different temperature conditions and restrictions on chain applications. These are values for that product range, not general cable-assembly rules. LAPP product and application data.
For one specific article, 1119885, LAPP lists an 8.1 mm nominal outer diameter and radius values of 32.4 mm fixed, 81.0 mm occasional and 121.5 mm continuously flexing. The example shows why copying the smallest figure into every routing condition would misread the evidence. Read the dynamic value with the full application limits; it does not establish unlimited cycle life or select that cable for a particular assembly. LAPP article 1119885.
When a supplier proposes another cable, request its own data and applicable movement conditions. Ask which diameter and tolerances underpin the routing calculation. Do not transfer the example's multipliers, cycle allowances or temperature limits to another construction.
Create a cable routing evidence table
Number each route segment on the drawing so a bidder can answer precisely. Include both end positions and the path between them when movement is involved.
On small screens, swipe or scroll sideways to read every column. Keyboard users can focus the table and use the arrow keys.
| RFQ field | Buyer supplies | Supplier evidence and release question |
|---|---|---|
| Cable identity | Required circuits, length and environment | Exact cable reference, construction and outer-diameter data |
| Movement duty | Fixed, occasional or repeated; travel, frequency, speed and acceleration | Manufacturer permission for the specified motion, including any torsion |
| Bend geometry | Available space and dimensioned route | Applicable radius, measurement convention and worst-position check |
| Load transfer | Handling loads and mounting locations | Restraint identity, attachment drawing and assembly instructions |
| Connector exit | Connector orientation and nearby obstacles | Supported exit arrangement and required straight section, if specified |
| Moving clearance | Adjacent parts and full travel envelope | Evidence addressing rubbing, trapping and unintended tension |
| Qualification | Intended duty and approval milestones | Test configuration, acceptance criteria and any uncovered conditions |
Treat this as a purchasing framework. The responsible engineer must establish the project limits and acceptance criteria; the table does not supply universal clamp spacing, tightening torque or test force.
For a cable carrier, igus advises following the cable or hose manufacturer's bend recommendations. Its installation guidance also addresses freedom of movement, avoiding twist and positioning strain relief; some allowances are specific to its chainflex products. Request instructions for the actual cable-and-carrier combination rather than copying those exceptions into an unrelated harness. igus cable carrier installation guidance.
Check the transition from restraint to moving cable
A quotation should identify the clamp, gland, backshell or other proposed restraint and the structure to which it attaches. Ask which cable diameter range and jacket construction the arrangement covers, and how its installation is controlled.
Require the drawing to identify the transition where restraint ends and bending begins. Ask whether the cable or connector manufacturer specifies a straight section or another exit restriction. Mark an unresolved requirement as open instead of inventing a distance from a photograph.
For enclosure entries, assess sealing and mechanical restraint as separate documented functions. The cable gland diameter and sealing guide covers the dimensional and ingress questions. An ingress label alone does not answer the routing table's load-transfer questions.
Compare two hypothetical quotations
The following comparison is invented for procurement training. It is not a customer case, supplier report or test result.
A buyer needs a harness for a tray that moves during every operating cycle. Drawing C provides the travel, temperature envelope, connector positions and available bend space.
Offer A quotes a cable reference and attaches only a fixed-installation radius. Its assembly photograph shows a restraint, but the restraint reference and mounting instructions are missing. Hold mechanical approval: request evidence for repeated movement and the complete restraint arrangement. A lower price cannot resolve these omissions.
Offer B identifies the cable and restraint references, returns an annotated drawing and supplies a motion-evaluation report. Before accepting it, compare the report's cable, geometry, travel, speed, temperature and termination arrangement with Drawing C. Record every difference and its technical disposition.
Accept the defined mechanical scope only when the relevant documents apply, the agreed qualification and sample checks pass, and the responsible engineer closes the deviations. If Offer B's report used a different route or leaves a required condition uncovered, keep that item on hold. “Tested” without the configuration is incomplete evidence.
Keep a short closure record for each hold: drawing segment, missing requirement, document requested, owner and accepted revision. Separate evidence missing from proposed configuration fails the requirement. The first needs applicable documentation; the second needs a revised proposal and renewed engineering review. This prevents an unanswered question from disappearing when a quotation is revised.
Make sample approval repeatable
Agree the sample identity, drawing revision, fixture and observations before evaluation. A useful record links the as-built routing photographs to the dimensions and restraint instructions being checked.
For an agreed movement evaluation, request the motion profile, cycle-count definition, environmental conditions, inspection intervals and acceptance limits. Identify who performed and reviewed the work. Let the responsible engineer define the evaluation safely; a buyer's informal hand-flex check does not establish service life.
Record slippage, jacket damage, interference and other specified observations against the agreed criteria. Require the specified post-evaluation checks and a disposition for each discrepancy. The harness electrical test report guide covers the separate electrical records; an electrical pass alone does not close an unverified mechanical duty.
Freeze the accepted cable, restraint, route and instructions in the purchase record. Require notification before substitutions or dimension changes that affect that approval.
Buyer FAQ
Can I use the fixed-installation radius for a moving tray?
Only if the exact cable manufacturer's evidence covers the proposed motion at that radius. Otherwise, obtain the applicable movement data and revise the route or cable selection through engineering review.
Does a flexible jacket prove repeated-bending life?
No. Request evidence for the cable construction and actual motion conditions. Ease of bending by hand does not establish an accepted cycle life for the assembly.
Can the supplier replace a clamp without changing the cable?
Require a documented comparison. Check the replacement's cable range, attachment, installation instructions and effect on the restraint-to-bend transition before approving it.
What should I send for price and lead-time confirmation?
Provide the route drawing, quantities, cable and connector requirements, movement conditions and required approval records. Request separate terms for samples, fixtures or evaluation work, and identify any unresolved technical milestones.
Send a cable routing inquiry
Use a consistent enquiry line for each drawing segment: drawing/revision; fixed or moving; cable identity and diameter; available radius; travel and motion profile; restraint arrangement; required qualification evidence; order quantity. Ask each bidder to return the same line with its proposed references and unresolved items.
Send a cable routing RFQ with the drawing, movement description, available bend space and restraint questions. Ask for the proposed component identities and evidence needed to close each open routing item.
Technical sources checked on 11 September 2026.