Overhead line accessories are the clamps, connectors and link fittings that hold a conductor to its insulators and towers and carry current across joints. They must grip without damaging the strands, survive decades of vibration and weather, and stay cool and corona-free under load. Metline supplies aluminium alloy clamps, compression sleeves, joints and jumper terminals matched to AAC, AAAC, ACSR and ACAR conductors, to utilities and contractors worldwide; the steel and copper-alloy parts of a string are described here so the aluminium items fit them.
A conductor is only as reliable as the hardware that holds it. Most overhead line failures that are not caused by storms start at a fitting: a clamp that abraded the strands, a joint that overheated, or a bolt that worked loose under aeolian vibration.
Line hardware falls into three functional groups. Suspension fittings carry the conductor's weight on tangent towers and allow it to swing. Tension fittings anchor the conductor at angle, terminal and section towers and must hold almost its full breaking load. Connecting fittings (shackles, clevises, links, eyes and hooks) join clamps to insulators and insulators to the tower, and set the geometry of the insulator string.
Around these sit the protective and current-carrying accessories: armour rods and preformed grips that shield strands at clamps, vibration dampers and spacers, mid-span compression joints, jumper terminals, and parallel-groove or bimetallic connectors at taps and transitions.
A cast or forged aluminium alloy body and keeper that cradle the conductor on tangent towers. The aluminium body is non-magnetic, so it adds no hysteresis or eddy-current loss and runs cooler than an iron clamp on high-current lines.
Trunnion designs pivot freely so the conductor can swing without bending at the clamp mouth. Double-support clamps share load across two insulator strings for long spans, crossings and high-security lines.
An elastomer insert and preformed rods spread the clamping force over a long length of conductor, reducing stress concentration and improving fatigue life where vibration is severe.
Helical preformed aluminium alloy rods wrapped round the conductor at the clamp to protect strands from abrasion and flashover burns.
A well-designed suspension clamp has a smooth, flared mouth with a radius sized to the conductor diameter, so the conductor leaves the clamp without a sharp bend. It also limits slip: high enough to hold the conductor in normal service, but low enough to let it slide under a broken-conductor event, protecting the tower from unbalanced load.
| Fitting | How it grips | Typical use |
|---|---|---|
| Compression dead-end | Steel sleeve pressed onto the core and an aluminium sleeve pressed over the strands with a hydraulic die | Transmission lines and any ACSR or high-tension AAAC; holds close to the full conductor strength |
| Bolted tension (strain) clamp | Conductor clamped in a cast aluminium body by U-bolts or keepers | Distribution lines and lower tensions; installed without compression tools |
| Wedge-type dead-end | Conductor locked by a self-tightening wedge in a tapered body | Distribution lines and LV aerial bundled cables |
| Preformed dead-end | Helical rods wrap the conductor and transfer load by friction over their length | Distribution and some sub-transmission lines; quick installation, no tools |
| Jumper terminal | Compression or bolted pad that carries current across the tension tower | Every dead-end tower; must be rated for the conductor's current and temperature |
Full-tension fittings are commonly required to withstand at least 95 % of the conductor's rated tensile strength without slip or failure, a criterion found in IEC 61284 and in ANSI C119.4 for connectors. When a line is uprated with a high-temperature conductor, dead-ends and jumper terminals must be qualified for the new continuous and emergency temperatures as well.
Connecting fittings form the mechanical chain between tower, insulator and clamp. They are usually hot-dip galvanised forged steel, sized by their specified minimum failing load, and they must couple correctly with the insulator ends.
Always check the failing load of every link against the string design load with the required safety factor, and confirm that coupling standards match between insulator and hardware.
| Material | Typical grades and processes | Advantages | Used for |
|---|---|---|---|
| Aluminium alloy | Cast Al-Si-Mg (e.g. A356-T6, EN AC-42100); forged or extruded 6061-T6 / 6082-T6 | Light, non-magnetic, same metal as the conductor so no galvanic couple, good corrosion resistance | Suspension and tension clamp bodies, compression sleeves, jumper terminals, spacers |
| Copper alloy | Bronze and brass castings, tinned copper | High conductivity and strength in a compact part | Copper-to-copper connectors, substation terminals; bimetallic transitions with aluminium |
| Galvanised steel | Forged carbon steel, hot-dip galvanised to ISO 1461 or ASTM A153 | Highest strength at lowest cost | Shackles, clevises, links, U-bolts, steel compression sleeves for ACSR cores |
| Ductile or malleable iron | Galvanised castings | Economical for complex shapes | Some clamp bodies and hardware on distribution lines |
Where aluminium conductors meet copper equipment, use bimetallic connectors or lugs with a friction-welded or explosion-bonded joint rather than direct contact, and apply contact grease to exclude moisture. On EHV lines, choose aluminium clamp bodies so magnetic losses do not heat the conductor at the clamp.
| Standard | Scope |
|---|---|
| IEC 61284 / EN 61284 | Requirements and tests for overhead line fittings: mechanical, electrical, corona and heat-cycle tests |
| IEC 60120 | Ball and socket couplings of string insulator units |
| IEC 60471 | Clevis and tongue couplings of string insulator units |
| IEC 61897 | Stockbridge-type aeolian vibration dampers |
| IEC 61854 | Spacers for overhead lines |
| ANSI C119.4 | Electric connectors for aluminium and copper conductors (North American practice) |
| ISO 1461 / ASTM A153 | Hot-dip galvanised coatings on iron and steel fittings |
Typical type tests include mechanical failing load, slip strength of clamps, heat-cycle tests on current-carrying fittings, magnetic loss on clamps, and corona/RIV tests at line voltage. Routine and sample tests cover dimensions, galvanising thickness and visual inspection on each lot.
Yes. The same families of fittings are used at every voltage; what changes is size, failing load, the number of strings and, above roughly 132 kV, the need for corona-controlled profiles and grading rings.
Aluminium is non-magnetic, so it does not create hysteresis and eddy-current losses around a high-current conductor. It is also lighter and galvanically compatible with aluminium conductors.
Not automatically. AAAC has no steel core, so compression dead-ends and joints use an all-aluminium design, and clamp grooves must match the AAAC diameter. Always select fittings for the exact conductor.
Most aluminium clamps and sleeves are standard catalogue items sized by conductor and failing load. Special aluminium fittings, such as custom jumper terminals or clamp bodies for unusual conductors, can be made to the customer's drawing.
Yes. Ordering conductor and aluminium hardware together lets us check that clamp grooves, compression dies and jumper terminals match the conductor exactly, and simplifies shipping and documentation.
Compression dead-ends hold nearly the full conductor strength and are standard for transmission lines and high tensions. Bolted clamps are quicker to install without hydraulic tools and are common on distribution lines with lower tensions.
Send the conductor, voltage and set quantities by tower type. We will reply with drawings, test documents and a delivered quote for the aluminium clamps, sleeves and terminals.
