Lightning Protection
Three metals meet in every earthing system. The Al/Cu interface is the weak spot — CUPAL strip and transition pieces remove it.
The problem you need to solve
A lightning protection system is inherently a three-metal system: copper ring earth underground, aluminium down-conductors on the façade, galvanised or stainless steel fasteners on the structure. The galvanic potential between Al and Cu is about 0.9 V — the chemistry that drives visible corrosion in any damp environment. Most designers focus on the geometry rules of EN 62305 (down-conductor spacing, conductor cross-section), but fewer focus on the fact that every component must also survive the EN 62561 impulse test — a 10/350 µs surge at the LPL peak current. A paste-and-bolt joint signals in a few years through visible façade corrosion that it is no longer in spec. And when lightning does strike, the highest current density lands exactly where the joint has already weakened.
How CUPAL solves it
CUPAL strip and transition pieces eliminate the Al/Cu galvanic couple at the joint. The aluminium side mates with the down-conductor, the copper side mates with the earthing mesh — one piece of material, two metals, joined by diffusion welding. No paste, no annual re-torque. The material is supplied in geometries that pass the EN 62561-2 component test (10/350 µs at the LPL peak current); the bond spreads the impulse energy across the full bonded surface rather than concentrating at the bolt hole. On the design side you size to EN 62305-1/-3 and VDE 0185-305-3; on the component side EN 62561-1/-2 gives you the guarantee that the joint actually carries the surge.
Lightning numbers that matter
Where the Al/Cu joint lives
Four common transitions where a lightning-protection system ages first.
Rooftop Al down-conductor → Cu ring earth
The problem you need to solve. An aluminium down-conductor comes down the façade and terminates onto the copper ring earth at ground level. The bolted joint sits exposed to weather; corrosion leaves visible staining on the façade in 4–8 years and raises earth resistance.
How CUPAL solves it. A CUPAL transition plate or strip between down-conductor and ring earth. Aluminium side to the down-conductor, copper side to the ring. EN 62561-2 component-tested geometry.
Telecom / power tower Al cabinet → Cu earthing mesh
The problem you need to solve. An aluminium equipment cabinet on a lattice tower bonds to the tower's copper earthing mesh. Thermal cycling plus regular LPL II (~150 kA) surges fatigue the bolted joint; impedance drifts over years.
How CUPAL solves it. A CUPAL bonding piece between cabinet and earthing mesh. The diffusion interface absorbs thermal and mechanical stress internally; the bolted joint does not loosen further.
Rooftop PV array equipotential bonding
The problem you need to solve. Aluminium mounting frame, copper PE conductor (≥6 mm² per EN 62305-5 guidance), steel fasteners — all on the same roof. A DC fault can drive surge current through the bonding path.
How CUPAL solves it. A CUPAL washer or strip in the frame-to-PE bolted joint. Bolt torque breaks through Al-oxide; the diffusion bond holds the interface inside; no new oxide can form.
Industrial chimney / tall mast down-conductors → earth
The problem you need to solve. Tall structures use multiple parallel aluminium down-conductors; an LPL II strike splits across them (~33 kA per conductor). Every Al/Cu bolted joint adds a voltage drop; across six joints, cascaded drops approach step-voltage limits.
How CUPAL solves it. A CUPAL transition plate on each down-conductor where it meets the earthing mesh. Low, stable transition resistance keeps the cascaded drop across the joints well inside tolerance during the strike.
Compared to alternatives
Three common approaches to a single Al/Cu lightning-protection joint.
| Approach | Initial transition resistance | EN 62305 inspection | Lead time | 20-year TCO / joint |
|---|---|---|---|---|
| Paste + Cu/Al bolted joint | Acceptable, drifts quickly | Annual visual + resistance test | From stock | High (inspection + rework) |
| Stainless hardware (separates Al from Cu) | More stable, but still an Al/Cu interface | Annual recommended | From stock | Medium |
| CUPAL bimetal transition (EN 62561-2 tested) | Stable | Extendable per EN 62305-3 Annex G | 2–4 weeks (custom) / stock (strip) | Low |
FAQs from lightning-protection designers
Recommended CUPAL products
Applicable standards for this field
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