Quick Answer / Summary: Terminate the conductor, close the shell fully over the jacket, fit the collar so bending load bypasses the joint, mark polarity at both ends, then check continuity and pull-test. A lead that passes all four steps will outlast one assembled without them by years, regardless of plug price.
The difference between a lead that lasts and one that fails at the plug is almost never the contact: it is strain relief, shell closure and whether anyone tested the joint before putting it into service.
Strain Relief Is the Whole Job
A plug concentrates all cable movement at the point where the conductor meets the terminal. A collar clamps the jacket and transfers that movement to the jacket, which is designed for it. Without a collar, the conductor work-hardens and breaks inside the shell, where the failure is invisible until the channel drops out.
Collar Types
Screw collars compress a tapered insert onto the jacket; push-fit collars rely on a moulded grip. Screw collars hold better on smooth jackets; push-fit suits soft rubber where compression could cut the insulation.
Heat Shrink as a Supplement
Adhesive-lined heat shrink over the collar-to-cable transition adds a second barrier and stops the jacket flexing at the collar’s edge. It is cheap and it is the single most effective addition to a DIY lead.
Closure, Marking and Testing
The shell must close completely: a partly closed shell exposes the terminal and reduces the grip the body provides. Marking polarity at both ends prevents the reversed-channel fault that is otherwise invisible. Testing is the last step and the one most often skipped.
Polarity Marking Methods
Coloured shells, coloured heat shrink or a printed label at each end. Whatever the method, apply it to both ends before the lead is coiled, because after coiling the ends are indistinguishable.
The Two Tests
Continuity end to end confirms the conductor path; a pull test confirms the mechanical joint. A lead that passes continuity and fails the pull test will fail in service, usually at the worst moment.
Re-Terminating Without Shortening
Cut back only to sound copper, not to the first sign of damage. Removing an extra few centimetres each time a lead is repaired is how a long lead becomes a short one after three repairs.
Assembly Checks
| Step | Requirement | Failure Mode |
|---|---|---|
| Conductor termination | Full insertion | High resistance |
| Shell closure | Fully seated | Exposed terminal |
| Collar | Clamps jacket | Conductor fatigue |
| Polarity mark | Both ends | Reversed channel |
| Tests | Continuity and pull | Intermittent failure |
Practical Applications
Building a set of leads for a system, re-terminating a lead that failed at the plug, standardising an assembly procedure for staff, and inspecting bought leads before use.
Frequently Asked Questions
Why do my banana leads fail at the plug?
Almost always missing strain relief. Without a collar clamping the jacket, all bending load reaches the conductor joint and the strands break inside the shell.
Does heat shrink help on a banana plug?
Yes. Adhesive-lined heat shrink over the collar-to-cable transition adds a barrier and stops the jacket flexing at the collar’s edge, which is where DIY leads usually fail.
How should I mark polarity on a lead?
With coloured shells, coloured heat shrink or labels at both ends, applied before the lead is coiled. Marking one end only is useless once the lead is stored.