Cable assembly types
Overmolded cable assemblies: when to specify them and what to ask
Overmolding encloses the connector-to-cable joint in molded plastic. Done well, it seals the joint, relieves strain and survives rough handling. It also adds a mold, a material choice and a process that a supplier has to control.
What overmolding is
In an overmolded cable assembly, the cable is terminated to its connector or contacts first, and then placed in a mold. Molten thermoplastic is injected around the termination, bonding to or mechanically locking onto the cable jacket and connector body. When it cools, the termination is enclosed in a single solid part that forms the strain relief and, where designed for it, a seal.
Some assemblies use an inner mold, sometimes called a pre-mold, to hold the wires in place and protect them before the outer mold is shot.
When overmolding is worth it
- Exposure to water, dust, oil or washdown, where the joint must be sealed.
- Repeated flexing or pulling at the connector, where a molded strain relief spreads the bending load.
- Rough handling: cables that are dropped, stepped on or dragged.
- Tamper resistance, where the termination should not be opened in the field.
- Consistent appearance and branding on a product that customers handle.
- Enough volume to justify the mold.
For low volumes, or where the termination may need repair, backshells, heat shrink with adhesive lining, or potting can be alternatives.
Low-pressure vs high-pressure molding
| Low-pressure molding | Conventional injection overmolding | |
|---|---|---|
| Typical materials | Polyamide and polyolefin hot-melt compounds | Thermoplastics such as PVC, TPU and TPE |
| Stress on the assembly | Lower pressure, gentler on fine wires, solder joints and electronics | Higher pressure; the termination must be protected or pre-molded |
| Tooling | Often aluminum molds | Aluminum or steel molds depending on volume |
| Common use | Encapsulating small electronics, sensors, delicate terminations | Rugged strain reliefs and sealed connector ends |
Pressures, temperatures and material grades vary by machine and compound. Ask the supplier which process they propose for your part and why.
Material compatibility
The overmold must bond or lock to the cable jacket. Similar material families generally bond better, for example a PVC mold on a PVC jacket, or a TPU mold on a TPU jacket. A mismatch can leave a joint that looks sealed but lets water track along the jacket. Specify the cable jacket and ask the supplier to confirm the molding compound is compatible with it, and with any chemicals the assembly will meet in service.
Tooling: what you are buying
- Mold cost and ownership. Ask for the mold to be quoted separately, and state who owns it and where it will be kept.
- Cavities. More cavities cost more up front and reduce piece price at volume.
- Mold life and maintenance. Ask how many shots the mold is expected to make, and who pays for refurbishment.
- Mold lead time. A new mold adds time before the first article. Ask for it separately from the production lead time.
- Design approval. Agree the molded shape, color, markings and any logo before the mold is cut; changes afterwards are expensive.
What to put in the specification
- Mold shape and dimensions, or a model, with critical dimensions identified.
- Molding material, hardness if relevant, color and any flammability rating required.
- Sealing requirement, stated as an ingress protection rating and the test that proves it.
- Strain relief performance, for example a flex test with a stated number of cycles.
- Markings on the mold: part number, logo, date code.
- Electrical tests after molding, because molding can damage terminations. See cable assembly testing.
- Workmanship criteria. IPC/WHMA-A-620 includes criteria for molding and potting; name the class.
Common overmold defects
| Defect | What it looks like | Why it matters |
|---|---|---|
| Short shot | Mold not completely filled | Exposed termination, weak strain relief |
| Voids and bubbles | Holes on the surface or inside | Leak paths, weak spots |
| Flash | Thin excess material at the mold parting line | Fit and appearance; can interfere with mating |
| Poor bond to jacket | Mold can be peeled or slid on the cable | Water tracking, loss of strain relief |
| Damaged termination | Opens or shorts found at test after molding | Scrap; molding pressure or heat not controlled |
| Burn or discoloration | Dark streaks | Material overheated, may be degraded |
Ask how the supplier inspects for each of these, and whether sectioning a sample mold is part of first article.
What to ask a supplier
- Do you mold in-house or through a partner, and who is responsible for mold quality?
- Which process and compound would you use, and have you molded onto this jacket material before?
- How do you check for voids, flash, short shots and incomplete bonding?
- What tests do you perform after molding?
- Who owns the mold, and can it be moved if we change suppliers?
Common questions
Can an overmolded assembly be repaired?
Generally not in a practical way; the mold has to be cut away, which usually means replacing the assembly. That is one reason to test after molding.
Does overmolding make a cable waterproof?
It can seal the termination if the materials bond and the design is right, but the connector's mating interface and the cable itself also need to be rated for the environment. Specify an ingress rating for the whole assembly and a test to prove it.
Is overmolding worth it for a prototype?
Usually not with production tooling. Prototypes often use heat shrink or a temporary strain relief, with the mold made once the design is stable.
Related: cable assembly vs wire harness, cost drivers, and lead times. For cables on trailers and cargo equipment, see the sister guide on PVC, PUR and TPE cable jackets.
Last reviewed 2026-09-17