Pull Force Testing: A Comprehensive QC Overview from a Wire Connector Harness Manufacturing Facility
In wire harness manufacturing, pull force testing is not just one test — it's a quality chain that spans from connector manufacturing to final QC. Each stage contributes a layer of assurance. Let’s break it down with a practical perspective and compare how Molex, cable assemblers, and QC teams handle this essential test.
What is Pull Force Testing?
Pull force testing evaluates the mechanical strength of a crimped connection or terminal insertion. It helps prevent issues like:
- Terminal back-out (loose fit inside the housing)
- Cold crimp (weak wire-terminal connection)
- Field disconnection due to vibration or movement
We typically distinguish between two tests:
- A. Housing Retention Force — Terminal locking into housing
- B. Pullout Force (Wire from Terminal) — Wire properly crimped into terminal
Pull Test Across the Supply Chain
To ensure every crimped terminal performs reliably in the field, pull testing is performed across multiple stages of production — each with a specific purpose and timing:
| Stage | What is tested | When it's done | Purpose |
|---|---|---|---|
| Connector Manufacturer | Terminal Housing Retention | At factory before shipment | Ensure terminals lock into housing correctly |
| Wire Harness Production | Pullout Force (Wire from Terminal) | Before production (crimp height setup) | Confirm machine setup is accurate |
| Wire Harness Production | Pullout Force (Wire from Terminal) - Sampling | Every 500–1000 pcs or tooling adjustment | Detect crimp drift or batch inconsistency |
| QC / Final Inspection | Continuity test + visual check | Final stage before packing/shipment | Double-check integrity and detect any human error |
Pull Force Standards (IEC & UL)
Based on IEC 60352-2:2013 and UL 486A/B, here’s a quick reference of required pullout forces by wire size:
| Wire Gauge (AWG) | Min. Pullout Force (IEC 60352-2) |
|---|---|
| 24 AWG | ≥ 28 N (IEC Standard) |
| 22 AWG | ≥ 40 N |
| 20 AWG | ≥ 60 N |
Note: Molex's internal specs (such as 22.2 N for 24 AWG) are minimums and may be lower than IEC for specific housing designs.
Common Issues Prevented by Pull Test
| Failure Type | Cause | Which Test Detects It? |
|---|---|---|
| Terminal push-out | Improper locking into housing | Housing Retention Test |
| Crimp | Insufficient crimp height or force | Pullout Test |
| Open circuit | Terminal not seated, wire break | Continuity / Visual Test |
| Crimp drift over time | Applicator setup not revalidated | Sampling Pull Test |
Our Best Practices
At Green Solar, we follow a two-stage pull test system:
- Pre-Production Setup: Verify applicator setup and crimp height with destructive pull test
- In-Line Sampling: Perform pull test every 500–1000 assemblies depending on batch size and tooling stability
- Continuity + Visual Check: Confirm every connector is properly locked and visually aligned
- Final QC: Conduct destructive sampling on end-of-batch pieces if required by customer
Want Peace of Mind with Your Harnesses?
Pull test is not an option — it's an essential part of quality design. If your current supplier skips or simplifies this, it may be time to upgrade.
Contact us to learn how we implement UL based pull testing tailored to your wire types, crimp specs, and industry compliance requirements.
Frequently Asked Questions
What is pull force testing in wire harness assembly?
Pull force testing checks the mechanical integrity of terminal-to-wire or terminal-to-housing connections. It ensures each crimp or insertion meets required strength standards.
When is pull force testing performed?
Pull testing is conducted at different stages—connector factory (housing retention), wire harness production (before setup and during batch sampling), but not during final QC.
What standards guide pull force testing?
Common standards include IEC 60352-2 and UL 486A/B. These specify minimum pullout forces depending on wire gauge and application.
Download Sample Pull Test Report
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