Memory Wire Composite Harness, Enameled Copper on Steel Core

What a memory wire composite harness actually does

A memory wire composite harness puts two metals in one cable and gives each one a different job. The enameled copper carries current. The stainless steel core underneath does no electrical work at all; it simply holds whatever shape you bend the lead into. That division of labor is what lets a small device keep its position without a clip, a bracket or an external stay, and it is why this construction shows up in products where the cable itself has to be a structural part.

The build we produce most often is straightforward: enameled copper wound around a single stainless shaping wire, then jacketed. Winding the conductor around the core rather than laying the two side by side keeps the assembly round, keeps it flexible enough to route, and gives one cable instead of two that would have to be taped or sleeved together later. Where the lead has to carry more current, we wind multiple conductors around the same core; where it has to resist repeated handling, we add a serving layer between the winding and the jacket.

One word matters more than the rest of this page: formable. See the next section before you send us a drawing.

Formable is not shape memory, and that difference decides your design

Two quite different materials get sold under the name memory wire. Confusing them is the fastest way to burn a round of samples.

We build the left column. A stainless core is formable and dead-set: you bend it, it stays. It is inexpensive, it is easy to work with, and for the great majority of products that is exactly what is wanted. If instead your device needs a wire that actively pulls back to a trained shape when current or heat is applied, that is a shape memory alloy actuator, it is a different industry with different suppliers, and it is not something this page covers. Tell us early if that is what you need so neither of us spends money finding out.

Which core does the job: solid, stranded, or served?

The core is the part that decides how the finished lead feels in the hand, and it is the first thing to settle.

If you are not sure, send us the shape you need the lead to hold and how many times it has to be re-bent in service. Those two answers narrow the field faster than any datasheet.

Why the enamel wears through on a steel core

This is the failure mode that catches people out, and it is specific to this construction. The enameled conductor is wound around a steel core, which means every time the lead flexes, the enamel on the inside of the winding rubs against the steel. Steel is harder than cured enamel. Over enough cycles it wears through, the copper touches the core, and depending on what the core is connected to you get a leak, a short, or an intermittent fault that only shows up when the lead is held at one particular angle.

Three things control how long that takes. The first is bend radius: a tight bend loads the winding much harder than a gentle curve. The second is whether there is anything between the copper and the steel, which is what the serving layer in the table above is for. The third is the enamel grade, and that one involves a real trade-off, covered next.

Solderable enamel or scrape-resistant enamel: you have to pick one

The enamel on the conductor has to do two jobs that pull in opposite directions. It has to survive being rubbed against a steel core, and it has to come off cleanly at the ends so the conductor can be terminated.

We strip solderable grades by controlled immersion, which removes the coating and tins the strands in one step. We do not claim to strip every enamel type with that method, and we will tell you plainly if the grade on your drawing needs a different process. Because the choice affects both cost and field life, the enamel grade is something we confirm with you before quoting rather than assume.

For background on how these coatings are classified, see the general reference on magnet wire.

How the steel core gets terminated

Stainless steel does not solder the way copper does. Standard rosin flux will not wet it, and a joint made with aggressive flux is not something we would put into a product that gets handled. So in most builds the core is not part of the electrical path at all: it is crimped, spot welded, or simply captured inside the overmold at the strain relief so it cannot migrate.

If your design does need the core bonded or grounded, say so on the drawing, because it changes the tooling. It also matters that stainless has roughly forty times the resistivity of copper, so the core is never a substitute for a conductor. If a lead needs both structural stiffness and real current capacity, the answer is a bigger copper conductor on a modest core, not a thicker core.

Where these harnesses get used

The same construction turns up in more places than most people expect. In personal care and wearable devices it is the element that lets an applicator head or a sensor pad keep contact without a clamp pressing on the user. In audio it is the formable hook that keeps a headset in place. In inspection equipment it is the neck that lets an operator aim a probe and let go.

Where the lead also has to be tested and documented to a wiring standard, our patient monitor ECG lead set and surgical handpiece cable with silicone jacket are built under the same build-to-drawing discipline. Devices that route a formable neck through a sealed wall usually pair this harness with a medical panel feedthrough set. If instead of holding a shape the assembly has to survive continuous motion, start from our surgical robot cable harness or custom industrial robot wire harness. Where the cable should retract rather than stay put, a coiled retractable cable is the better starting point. And for imaging heads that combine a formable neck with many coax elements, see the ultrasound probe cable assembly.

What we need from you to quote

How we build and inspect them

We assemble in Shenzhen with four production lines and around forty assembly operators, and we cut our own tooling in house, which is why a custom overmold does not add weeks to the schedule. Typical minimum order quantity is 500 pieces, samples ship in about three days, and production runs in about fourteen days depending on the process. Every assembly is built and inspected to IPC-WHMA-A-620 Class 3 and receives a 100% continuity and pinout test before it leaves the floor.

Frequently asked questions

Everything on this page is general guidance. Each harness is built and inspected to your drawing.