industry news 10/06/2026 0
Overlap connections are the most common way to join zig zag wire sections in the field. They are also the most common source of failure when the spec is not followed. A connection that looks acceptable to the naked eye can still fail under load if the overlap length, crimp depth, or wire alignment falls outside the accepted range. This guide lays out the actual standard specifications used by fabricators, installers, and inspectors on real projects, not generic recommendations from a manual nobody reads.
The minimum overlap length is not a suggestion. It is a structural requirement. Getting it wrong means the joint will slip, rotate, or open under tension. The required length varies by application, but the principle stays the same: more bend cycles in the overlap means more mechanical grip.
For most non-structural applications such as fencing, barrier mesh, and light-duty screening, the minimum overlap is two full zig zag cycles. A full cycle means one peak plus one valley, measured from the start of one bend to the start of the next identical bend. On typical wire with a 20mm to 30mm pitch, this translates to roughly 40mm to 60mm of overlap.
Two cycles is the absolute minimum. Three cycles are preferred for any application exposed to wind, vibration, or repeated loading. The extra cycle adds significant resistance to slippage without adding much material or installation time.
For structural or load-bearing applications, the overlap extends to four or five full cycles. This is common in embedded concrete reinforcement, heavy-duty fencing, and industrial barrier systems. The longer overlap distributes the load across more bend points, reducing stress at any single location.
Overlap length must scale with pitch. A wire with a 15mm pitch and a wire with a 40mm pitch cannot use the same overlap dimension and expect the same performance. The spec is based on cycles, not millimeters. Always count the cycles, not the ruler.
If you are joining two wires with different pitches, use the smaller pitch as the basis for calculating overlap cycles. This ensures the joint has enough grip even at the tighter bend spacing. A joint designed for the larger pitch will have insufficient grip where the smaller-pitch wire is concerned, and that is where the failure will start.
The overlap length gets the wire in position. The crimp is what locks it there. A shallow crimp holds nothing. An overly deep crimp cracks the wire at the bend point. The depth and angle must fall within a narrow window.
Crimp depth is measured from the original wire surface to the lowest point of the compressed section. For zig zag wire, the acceptable range is between forty percent and sixty percent of the wire diameter. On a 3mm wire, that means a crimp depth of 1.2mm to 1.8mm.
Less than forty percent and the crimp does not fully engage the wire profile. The peaks and valleys are not compressed enough to create a mechanical lock, and the joint slips under light tension. More than sixty percent and the wire begins to crack at the bend points. The metal work-hardens and loses ductility. A crimped wire that has been over-compressed will snap at the crimp point long before the rest of the wire reaches its limit.
Use a crimping die that matches the wire diameter exactly. A die that is too large produces a shallow crimp. A die that is too small produces an overly deep crimp. There is no compensation. The die must match the wire.
The crimp tool must contact the wire at both the peak and the valley of the zig zag profile simultaneously. If the die only contacts one side, the crimp is incomplete and the joint will rotate under load.
The crimp angle should be between 120 degrees and 150 degrees relative to the wire axis. This range ensures the wire is bent into a locking shape without being folded flat. An angle below 120 degrees flattens the bend and eliminates the spring action that holds the joint together. An angle above 150 degrees does not compress the wire enough to create a lock.
Check the crimp angle on the first three joints of every batch. After that, check every tenth joint. If the angle drifts outside the range, stop and recalibrate the tool before continuing.
Two pieces of zig zag wire can have the same nominal specification and still not match well enough for a reliable overlap joint. Tolerances matter. The closer the match, the stronger the joint.
Wire diameter tolerance for most zig zag wire products is plus or minus 0.05mm to 0.1mm. When joining two pieces, the diameter difference between them should not exceed 0.05mm. A larger difference means one wire compresses more than the other during crimping. The thinner wire deforms permanently while the thicker wire barely moves. The joint is lopsided and weak on the thin-wire side.
Measure both wires with a micrometer before joining. Not a caliper. A caliper does not have the resolution to catch a 0.05mm difference reliably. If the diameters do not match, sort the wire by diameter and join like with like.
The zig zag pitch must match within plus or minus 1mm. The bend angle must match within plus or minus 3 degrees. These tolerances sound tight, but they are necessary for the overlap joint to seat properly.
Lay both wire pieces side by side on a flat surface and look at the shadow line cast by overhead light. If the shadows do not run parallel, the pitch or angle is off. Rotate one piece until the shadows align, then mark the joint position. This takes thirty seconds and prevents a joint that will never sit right no matter how hard you crimp it.
A joint that passes visual inspection can still fail under load. Testing standards exist for a reason. The most common field tests are pull tests and bend tests, and both have specific pass criteria.
Grip both wire sections on opposite sides of the joint and apply steady tension. The joint must hold a pull force equal to at least seventy percent of the wire’s minimum breaking strength. For a wire rated at 500 Newtons breaking strength, the joint must hold 350 Newtons without slipping or separating.
Apply the force slowly. A sudden yank does not test the joint. It tests your grip. Increase tension at a rate of about 50 Newtons per second. Hold the target force for ten seconds. If the joint holds for the full ten seconds without movement, it passes. If it slips at any point during the hold, it fails.
Test a minimum of five joints per hundred meters of installed wire. If more than one joint fails in a batch of five, the entire batch must be re-crimped and re-tested. There is no partial acceptance.
For applications where the joint will experience repeated loading, such as spring assemblies or vibrating screen supports, a static pull test is not enough. The joint must also pass a cyclic bending test.
Flex the joint through its full range of motion at a rate of one cycle per second for five hundred cycles. After the five hundred cycles, perform the pull test again. The joint must still hold seventy percent of breaking strength. If the pull strength has dropped below that threshold, the joint has fatigue damage and must be replaced.
This test mimics real-world conditions. A joint that passes a static pull test but fails after five hundred cycles will fail in the field within weeks. Do not skip this test on any fatigue-critical installation.
The joint is the most vulnerable point in any zig zag wire assembly. It is where two wires meet, where crimping has damaged the surface coating, and where moisture collects between the overlapping profiles. Environmental specifications protect the joint from the thing that kills it fastest: corrosion.
If the zig zag wire is coated, galvanized, or painted, the coating must remain continuous across the joint. The crimping process scrapes and compresses the coating at the overlap point. This is unavoidable, but the exposed metal must be protected.
Apply a zinc-rich coating or cold galvanizing compound to the crimped area after installation. The coating must cover the entire overlap zone, not just the crimp point. Moisture gets into the joint from the edges, not just the center. A coating that covers only the middle leaves the edges exposed, and corrosion starts there.
For outdoor installations, the coating must be rated for the expected service environment. Coastal installations require a heavier coating than inland installations. The spec does not change. Only the coating rating changes.
The overlap joint creates a crevice between the two wire profiles. That crevice traps moisture, dirt, and debris. Over time, this accelerates corrosion at a rate three to five times faster than on exposed wire.
Seal the joint with a flexible sealant or a self-fusing tape after crimping. The sealant must remain flexible after curing. A rigid sealant will crack as the wire flexes under load, reopening the crevice. Silicone-based sealants and butyl tapes work well. Epoxy does not, because it is too rigid for a joint that moves.
Inspectors see the same violations repeatedly. Most of them are preventable.
This is the number one violation. Installers cut the overlap short to save time or material. A one-cycle overlap on a wire that specs two cycles is a joint waiting to fail. It may hold during installation but will open under the first real load event.
A 2.5mm wire crimped to a 3.0mm wire at the same joint. The spec requires matched diameters. This violation happens when installers grab wire from different bundles without checking. Sort your wire before you start. It takes five minutes and prevents a failure that takes five hours to fix.
Using a generic crimping tool that does not match the zig zag profile. A flat-wire crimp die does not contact the peaks and valleys of zig zag wire properly. The crimp looks fine but only grips one side of the profile. The joint rotates and loosens under vibration. Always use a die that matches the specific wire profile you are working with.
The joint is crimped, the installer moves on. No pull test, no visual check, no angle verification. This is how bad joints get buried in the wall or hidden under mesh where nobody can see them until they fail. Every joint must be inspected before it is covered or concealed. There are no exceptions.