Long-barrel vs standard-barrel lugs

What barrel length actually changes

The barrel is the tube that receives the conductor. Its length is measured from the conductor entry to the palm. A standard barrel takes one crimp near the palm end. A long barrel takes two crimps, spaced along the barrel, with the second one closer to the conductor entry.

The extra length is not cosmetic. It changes the strip length, the crimp schedule, the pull-out strength and the depth of terminal space the lug needs behind the stud. It also changes the bending stiffness of the termination, because a longer rigid barrel moves the flex point further back along the cable.

A common mistake is to treat barrel length as a quality grade. A long barrel is not a premium version of a standard barrel. It is a different joint design for a different duty, and on a short cable tail in a shallow enclosure it can be the wrong part.

The standard barrel

A standard barrel is sized so one crimp covers the conductor bundle. The die compresses the barrel in a single pass, and the crimp position is set by a stop on the tool or by a mark on the barrel. Cycle time is short and the tooling is simple.

The limit is the load path. With one crimp, the transition from the crimped zone to the free conductor happens over a short distance. Under tension, the strands at the edge of the crimp carry more load than the rest. That is acceptable for a static joint with a modest pull-out requirement, which covers most panel wiring.

Standard barrels also suit shallow terminal boxes, because the palm can sit close to the cable entry. If the enclosure depth is fixed and the cable has to bend immediately behind the lug, the shorter barrel reduces the bend radius the cable sees at the termination.

Strip length is easier to control on a standard barrel. The conductor only has to fill a short tube, so the tolerance on the strip is wider and the insulation gap is less sensitive to the operator. On a high volume line where the strip is made by a machine and checked by eye, that simplicity is a real advantage.

The long barrel and the second crimp

A long barrel allows two crimps. The first sits near the palm and the second near the conductor entry. The second crimp grips the conductor further back and spreads the transition over a longer length, which raises the pull-out strength and reduces the chance of strand movement under cyclic load.

The second crimp must be made with the correct die and the correct spacing. Two crimps placed too close together do not add much, and two crimps that overlap can crack the barrel. The lug datasheet normally states the crimp positions, and the die often has a locator that sets them.

Long barrels are common on heavy power cables, on connections that see vibration, and on aluminium conductors where creep over time is a concern. They are also used where the cable is pulled into position after termination, because the longer grip resists the pull.

Comparing the two barrel lengths

The table below compares the two designs on the points that change a drawing or a work instruction. Read it alongside the cable class, because a fine-strand conductor behaves differently in a long barrel than a coarse stranded one.

One row deserves a note. Cycle time is often underestimated because it is measured per crimp, not per cable. Two crimps add a second tool stroke, a second check and a second chance for the operator to place the die in the wrong position. On a high volume line that is a real labour cost, not a rounding error.

Pull-out strength and how it is proven

Pull-out strength is the tensile load at which the conductor either pulls out of the barrel or the barrel fails. It depends on the barrel diameter relative to the conductor, the crimp depth, the number of crimps and the conductor class. A long barrel usually improves the result because the load is shared over two crimped zones.

The test is a tensile pull on a prepared sample, with the load applied along the conductor axis and the palm restrained. The acceptance value comes from the product standard or from the drawing. IEC 61238-1 includes mechanical tests as part of the connector qualification, and the sample size and rate of loading should be recorded.

Do not read a pull-out figure as a working load. It is a qualification result from a sample, not a safe continuous load for the installed joint. The installed joint also sees thermal cycling, vibration and corrosion, none of which a single pull test covers.

Look at where the sample fails, not only at the load it reached. A conductor that pulls out of the barrel with clean strands points to insufficient crimp depth or a barrel that is too large. A barrel that splits points to a die or wall thickness problem. A conductor that breaks outside the barrel, away from the crimp, is the better result because it means the joint outlasted the wire.

Terminal space and the palm

A long barrel needs room behind the palm. Check the distance from the stud centre to the nearest wall, the cable gland or the next phase. If that distance is shorter than the barrel plus the bend radius of the cable, the lug will force the cable into a tight bend or press against an edge.

The palm angle matters too. A 90 degree palm with a long barrel projects the barrel sideways, which can be worse than a straight palm in a shallow box. Check the assembly in three dimensions rather than on the drawing alone.

On multi-phase terminals, the barrel of one lug can reduce the clearance to the next phase. Phase spacing is an insulation and creepage decision, so a longer barrel that closes a gap is a design change, not just a purchasing change.

How to specify barrel length

State the barrel type, the conductor size and class, the crimp count and the die reference on the drawing. Add the strip length and the crimp positions, or refer to the manufacturer's crimp schedule by part number. If the joint must meet a pull-out value, state the test standard and the sample size.

For a new part, ask for a sample with both crimps made and a pull test result. Check the barrel against the actual cable, not a nominal size, because a flexible conductor can measure smaller than its nominal area once the strands are compacted.

If the terminal depth is tight, do not solve it by cutting the barrel down or by crimping only the front half. A shortened barrel loses the second crimp and the strip control that the part was designed around. Change the palm angle, move the stud or use a standard barrel instead.

• Barrel type and part number, not just barrel length in millimetres
• Conductor size and class, with the cable standard
• Number of crimps and their positions
• Die reference for each crimp
• Strip length and the maximum insulation gap
• Terminal depth available behind the palm
• Pull-out requirement and test standard