Why a Bare Stranded End Fails Under a Screw
The failure is mechanical before it is electrical. A screw clamp is sized for a defined cross-section, but stranded wire compresses unevenly. The outer strands creep out of the clamping zone at the edges; the effective contact area drops, and joint resistance rises. Heat accelerates the cycle until the connection runs hot or trips a drive.
Fine-stranded conductors are the worst case. Individual strands are thin enough to shear at the clamp edge during installation, and every service cycle removes a few more. Control-cabinet standards assume a prepared wire end for exactly this reason - the remaining question is which end form to prepare.
Solid, Stranded, or Fine-Stranded: Preparing the Conductor
Solid wire holds its shape under a screw and often needs no end treatment in dry, fixed installations. Stranded wire is where the decision starts. Fine-stranded classes - the flexible conductors used in robotics, e-mobility, and vibration-heavy enclosures - should always carry a prepared end, because their strands are the first to shear and the hardest to re-terminate in the field.
Strip length is the second half of the spec. Too short and the crimp grips insulation instead of copper; too long and bare conductor shows behind the collar, inviting a short in tight rows. A drawing that fixes strip length per wire size removes the judgment call from the bench.
Pin Terminal, Ferrule, or Ring Tongue: Matching the End to the Clamp
The end form is not a styling preference; it follows the clamp hardware.
|
End form |
Where it fits |
Limit to plan around |
|
Insulated pin terminal |
Screw-clamp terminal blocks in tight rows; the plastic collar keeps the pin aligned and stops strands fraying back |
The collar adds width - check the block pitch first |
|
Bare pin end |
Spring-cage and push-in clamps too narrow for a collar |
No insulation stop, so strip length must be controlled |
|
Wire-end ferrule |
The standard for spring-cage terminals per DIN 46228 |
Each conductor size needs its matching crimp die |
|
Ring tongue |
Stud and bolted joints |
Cannot enter a side-entry terminal block |
When a panel mixes screw clamps and stud lugs, the harness usually ends up with two prepared end forms per conductor. Ordering both from one supplier keeps sleeve colors and crimp tooling consistent across the whole build, which is a quieter benefit than it sounds during production ramp-up.
Pin Machining Changes
Stamped thin strip and rolled pin ends are most common. In volume, this method is cheap and reliable, but the junction may require a pin diameter matched to a clamp, a pin length trimmed to a strip dimension, or a material swap for the workplace.
, KEY-CNC turns pin terminal connections from free-cutting, dimensionally stable C36000 brass bar or contact resistance-driven C11000 copper. Stainless 303/304 is for vibration-corrosion joints. To prevent chips from entering the terminal block, all contacts are deburred and ultrasonically cleaned. Pin diameter and concentricity are kept to 0.01 mm. Before packaging, CMM and digital callipers check batches against the drawing.
The drawing rules because the part is machined, not stamped. In control panels made in small series with extended service lives, where one clamp family must be served exactly, machined pin ends are used since non-standard diameters, tip chamfers, and mixed materials within one harness are first-pass possibilities, not tooling requests.
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