Quick Answer / Summary: Moulded assemblies add a polymer strain relief bonded to the cable jacket and connector. Specify the material, hardness, IP rating, bend and pull requirements, and tooling ownership. Test with a pull test and a bend test, not only an electrical check.
Overmoulding is the difference between a cable that survives being pulled and one that fails at the connector. It is also the least understood line in a custom assembly quote, because the material and the tool are invisible in the finished part.
Overmoulding is a mechanical specification with a tooling cost.What Overmoulding Actually Does
The mould encapsulates the connector-to-cable junction, replacing a boot or a crimp with a bonded polymer transition. The result is mechanical, not electrical.
Strain relief and sealing
A well-formed overmould spreads bending force over a length of jacket rather than concentrating it at the connector. With the right material and adhesion, it also provides an ingress protection rating that a loose boot cannot achieve.
Where it fails
Poor adhesion between jacket and mould creates a path for water and a stress point just behind the mould. This is a process problem, not a design problem, and it shows up as field failures rather than inspection rejects.
Material and Hardness Choices
The mould compound decides flexibility, chemical resistance and appearance. It also decides whether the assembly can be repaired.
Common materials
TPU and PVC dominate; TPE appears where flexibility matters. Each has a different temperature range and chemical resistance, and a supplier that cannot name the material cannot support a failure analysis.
Hardness and feel
Shore hardness affects how the assembly handles and how it wears at a panel entry. A soft mould feels better but can tear; a hard mould protects but transfers stress to the jacket. The right choice depends on how the cable is routed.
Specification and Testing
Moulded assemblies need mechanical acceptance criteria, because the electrical test says nothing about the part that fails.
What to specify
IP rating if required, pull strength, minimum bend radius, operating temperature and any chemical exposure. Add the colour and any marking requirement, because moulded parts cannot be re-labeled after production.
What to test
Pull test to the specified load, bend test around the minimum radius, visual inspection of the mould for flash and voids, and the electrical or optical test appropriate to the cable. A sample flex test is worth adding for cables that move in service.
Tooling and Commercial Reality
Moulding requires a tool, and the tool is the reason moulded assemblies have minimums.
Tool cost and ownership
A new mould is a real cost, often several thousand dollars. Ask whether it is charged once, amortised or owned by you, and record its location. Buyer-owned tooling is the only way to move a design to a second source.
Minimums and lead time
Expect a minimum run per mould and a lead time that includes tool making on the first order. Subsequent orders are faster, which is why the second order is usually much cheaper than the first.
Moulded Assembly Specification Sheet
| Parameter | What to state | Test method |
|---|
| Material | TPU, PVC or TPE with grade | Material certificate |
| Hardness | Shore A or D target | Durometer check |
| Ingress protection | IP rating if required | Sealing test |
| Pull strength | Load in newtons | Pull test to load |
| Bend radius | Minimum operating radius | Bend test |
| Temperature | Operating range | Material datasheet plus sample |
Practical Applications
Moulded assemblies are used in industrial machines, outdoor and washdown environments, medical carts, automotive test rigs and any cable that is plugged and unplugged frequently. They are also common where a cable exits an enclosure and needs a sealed transition. For assemblies that will be handled daily, ask for a sample with the production mould rather than a machined prototype. A prototype can be perfect and unrepresentative, because the moulding process that produces the volume part has different flow, adhesion and cooling behaviour. Testing a production-mould sample for pull strength and bend life is the only way to know how the part will behave after the first thousand insertions. Ask whether the mould tool is single or multi-cavity, because it changes both the unit price and the lead time. A multi-cavity tool costs more up front and produces faster, which matters when the first order is large. For small orders, a single-cavity tool is usually the better compromise, and the supplier should be able to explain the trade-off in numbers rather than in generalities. Ask for the mould maintenance schedule and who performs it. A mould that is not maintained produces flash, short shots and inconsistent sealing, and those defects appear gradually rather than all at once, which makes them easy to attribute to the wrong cause.
Reviewed by ZONG Cable Editorial | Last updated: 3 November 2026 | Reviewed against TIA-568 structured cabling practice and ISO/IEC 11801 fiber channel requirements.
How this guide was built: Moulding guidance covers material, hardness, sealing and mechanical acceptance, which are the parameters that decide field life. Electrical and optical tests are treated as separate acceptance criteria because they do not measure the mould.
Disclosure: We do not mould cable. Confirm material grade, tooling ownership and mechanical test criteria in the order.
Frequently Asked Questions
What is a moulded cable assembly?
An assembly where a polymer mould is formed over the connector and cable junction to provide strain relief and, where specified, sealing.
Does moulding improve electrical performance?
No. It improves mechanical robustness and sealing. Electrical performance comes from the cable and connector.
Why is the first order more expensive?
Because it includes tool making. Later orders reuse the tool and are cheaper per unit.
Can a moulded assembly be repaired?
Usually not. The mould is bonded, so a failure means replacement rather than re-termination.
What test matters most?
A pull test plus a bend test at the specified radius. Electrical tests will not reveal a weak mould.
