Key takeaways
- The conductor class decides whether a ferrule is needed and which barrel will accept the strands.
- A ferrule sized only by nominal area can be loose on a fine strand cable or tight on a coarse one.
- The crimp profile and the tool are part of the ferrule selection, not an afterthought.
- Inspect the strand entry and the barrel fill, then prove the joint with a pull test.
What a ferrule does
A ferrule, sometimes called a cord end terminal or an end sleeve, is a thin metal tube that is crimped over the stripped end of a flexible conductor. It keeps the strands together, gives the terminal block or clamp a solid surface to grip and reduces the chance of a strand straying outside the clamp.
It is not a current carrying device in the same sense as a lug. Its job is to make the conductor end predictable. A ferrule that is the wrong size can leave voids, cut strands or sit loose in the clamp, and the resulting joint may pass a visual check and fail a pull test.
The selection has to match the conductor, the clamp and the crimp tool. Those three are linked, and changing one without the others is how a good ferrule becomes a bad joint.
Start with the conductor class
IEC 60228 defines conductor classes. A class 2 stranded conductor has fewer, thicker strands. A class 5 or class 6 flexible conductor has many fine strands. The finer the strands, the more a ferrule helps, and the more the barrel has to contain without damaging the wire.
A ferrule sized only by nominal cross-section can be too loose on a fine strand cable because the actual strand bundle diameter is different from a coarse stranded cable of the same area. The result is a barrel with voids or a conductor that pulls back during crimping.
Check the conductor class and the strand count before the ferrule. If the cable is a special flexible type with a high strand count, ask the ferrule supplier for the recommended barrel rather than assuming the standard size will do.
Single, twin and sleeved ferrules
A single ferrule takes one conductor. A twin ferrule takes two conductors into one barrel, which is useful where two wires land in the same terminal. The twin version needs a tool and a die that match its shape, and the two conductors should be the same size.
A sleeved ferrule has a plastic collar that covers the barrel and the conductor insulation. The collar helps with insertion depth and gives some mechanical support, but it is not a seal and it does not add a voltage rating. An unsleeved ferrule is smaller and can be used where space is tight or where a separate cover is fitted.
Long ferrules are used where the clamp is deep or where a longer crimp is needed. They add length and cost. A standard ferrule in a deep clamp can leave the crimp outside the clamp, which is worse than a long ferrule.
Sleeve, colour and marking
Many plants use a colour code on the sleeve to indicate the cross-section. The code is a convenience, not a proof. A wrong colour on a correct barrel can happen, and a correct colour on a wrong barrel is harder to see. Check the marking and the fit, not only the colour.
The sleeve should sit over the barrel and the insulation without being trapped in the crimp. If the sleeve is pushed too far forward, the crimp can deform it and the conductor entry becomes a weak point. If it is too far back, the barrel is exposed and the insertion depth is harder to judge.
Some ferrules are marked with the cross-section and the standard. That marking is useful for traceability after the joint is made, especially in a panel where the wire is later covered by a duct or a bundle.
The sleeve also affects the bend. A stiff collar close to the barrel can concentrate bending at the crimp exit, while a longer flexible collar spreads it. If the wire turns immediately after the terminal, check the bend with the sleeve fitted, not on a bare barrel.
Crimp profile and tool
The common ferrule crimp profiles are square, trapezoid, hex and a four-indent form. The profile changes the contact area, the pull-out strength and the shape that has to fit the clamp. A square or trapezoid profile is common for terminal blocks because it presents a flat face to the clamp screw.
The tool has to match the ferrule and the profile. A generic plier type tool can crush the barrel without controlling the crimp height. A ratchet tool with a fixed die is more repeatable, and a tool with a die for each size range is better than one die for everything.
The crimp height or the die setting should be stated. If the tool has a calibration or a go/no-go gauge, use it. A tool that has been dropped or adjusted without a check can produce a joint that looks right and pulls out below the required force.
The ferrule and the die are one selection
A correct ferrule with the wrong die is an incorrect joint. Choose them together and prove them on the actual cable.
Strip length and insertion
The strip length should leave enough conductor to fill the barrel and no more. Too little and the barrel is short of strands. Too much and bare conductor sits outside the ferrule, which can short to a neighbouring terminal or corrode.
The sleeve usually sets the insertion depth. Push the conductor until it stops at the collar, then check that the strands are visible at the far end of the barrel before crimping. For an unsleeved ferrule, mark the strip length on the tool or use a strip gauge.
Fine strands are easy to bend back during insertion. A twisted or folded strand bundle can enter the barrel partly and leave a void. A small twist in the direction of the strand lay, without crossing the strands, helps. A badly twisted bundle is worse than a straight one.
Inspection and pull test
Check the barrel fill, the strand entry and the crimp shape. The barrel should be full, the strands should not be cut at the entry and the crimp should be symmetrical with no cracks. The sleeve should not be trapped or split.
A pull test is the usual proof. The sample size and the acceptance value should come from the product standard, the terminal supplier or the customer requirement. A visual check alone does not show whether the barrel is full or whether the tool is set correctly.
For a critical joint, cut a sample and inspect the cross-section. The section shows voids, folded strands and the wall thickness after crimping. It is the only way to see what the outside hides. Keep the section with the first article so a later change in the tool or the ferrule can be compared against it.
- Conductor class and strand count match the ferrule
- Strip length leaves the barrel full without bare wire outside
- Sleeve not trapped, split or pushed past the barrel
- Crimp profile matches the clamp and the tool
- Pull test at the stated sample size
- Cross-section on a sample where the joint is critical
The selection sequence and a comparison table
Classify the conductor, measure the strand bundle, choose the ferrule type and length, select the sleeve, match the crimp profile and tool, then prove the joint. The sequence is short, but each step depends on the one before it.
| Conductor class | Typical ferrule | Crimp profile | Watch |
|---|---|---|---|
| Class 2, coarse stranded | Single, standard length | Square or trapezoid | Barrel may be loose on the strand bundle |
| Class 5, flexible | Single, standard or long | Square or trapezoid | Fine strands can fold at insertion |
| Class 6, very flexible | Single, long sleeve | Square or hex | High strand count needs the correct barrel |
| Two wires in one clamp | Twin ferrule | Twin die profile | Both conductors must be the same size |
| Deep clamp | Long ferrule | Square or trapezoid | Crimp must sit inside the clamp |
| Tight space | Unsleeved ferrule | Square or hex | Insertion depth needs a gauge |
The table is a starting point. Confirm the ferrule and die against the actual cable and clamp.
Frequently asked questions
When should I use a ferrule?
Use one on a flexible conductor when the clamp or terminal block is designed for a solid end, or when fine strands could stray or be damaged. The conductor class, the clamp type and the project standard decide whether it is required.
Does the ferrule colour tell me the size?
It often indicates the cross-section, but it is a convenience rather than a proof. Check the marking and the fit on the actual conductor. A wrong colour on a correct barrel can happen.
Which crimp profile is best for a ferrule?
It depends on the clamp and the terminal. Square and trapezoid profiles present a flat face and are common for terminal blocks. Hex and indent profiles are also used. Match the profile to the tool and prove it with a pull test.
Can I crimp a ferrule with a generic tool?
A generic tool can crush the barrel without controlling the crimp height. A ratchet tool with the correct die is more repeatable. If a generic tool is used, check the crimp height and run a pull test on a sample.
Sources and further reading
- IEC 60228, Conductors of insulated cables
- DIN 46228-1, Tubular end sleeves
- DIN 46228-4, Twin tubular end sleeves
Qumek Engineering Desk
Engineering team
The engineering team behind Qumek drawings, DFM notes, tolerances and inspection standards. Every guide is reviewed against the drawings and processes used on live programmes.
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Send the conductor class, the clamp and the tool. The engineering desk will check the barrel, the sleeve and the crimp profile together.
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