Preventing galvanic corrosion between copper and aluminum

Galvanic corrosion (also called contact corrosion or bimetallic corrosion) is one of the most common problems in the electrical industry whenever dissimilar metals — typically copper and aluminum — are brought into direct contact. This article explains why it is dangerous, what consequences it can produce, and how the CUPAL bimetal material solves it.

What is galvanic corrosion?

Galvanic corrosion is an electrochemical process that occurs when two dissimilar metals are placed in direct contact in the presence of an electrolyte (moisture, humidity, condensate). The electrochemical potential difference between the two metals drives an electric current; the less noble metal (the anode) gradually dissolves — corrodes.

The electrochemical series

To understand galvanic corrosion, it helps to know where the metals sit in the electrochemical series:

The thermodynamic standard-potential difference is close to 2 V, but that is only an upper bound for pure metals in special electrolytes. In practice — on copper and aluminum electrodes covered with passive oxide films installed in equipment — the open-circuit voltage of the Cu/Al galvanic pair typically settles around ~0.5–1 V depending on the state of the passive layer. The driving force is nevertheless permanently present, which is why a direct Cu/Al joint corrodes progressively in the presence of moisture.

Why is the copper-aluminum combination particularly dangerous?

In electrical distribution it is extremely common for copper cable lugs to connect to aluminum busbars. This pairing is dangerous for several reasons:

1. Significant potential difference

As shown above, the thermodynamic potential difference between copper and aluminum is one of the largest among practical metal pairs; even with passive films, a ~0.5–1 V driving force for galvanic corrosion remains.

2. Moisture presence

Switchgear, distribution boards and outdoor installations almost always have moisture present — either as condensate or as humidity in the air. This provides the electrolyte for the galvanic cell.

3. Growth of aluminum-oxide layer

When the aluminum surface corrodes, an aluminum-oxide layer forms — an electrical insulator. This oxide layer increases the joint's contact resistance.

4. Loosening joints

Corrosion products (aluminum oxide) have larger volume than the original metal, which physically loosens bolted joints.

Real-world consequences

Galvanic corrosion at copper-aluminum joints has serious practical consequences:

Rising contact resistance

The oxide layer and corrosion products increase contact resistance. That leads to temperature rise at the joint, which further accelerates corrosion — a self-sustaining cycle.

Overheating and fire risk

Increased contact resistance generates heat. In high-current applications this temperature rise can reach fire-hazard levels. This is not a theoretical risk — many documented fires trace back to inadequate copper-aluminum joints.

Failure and outages

Loosening, corroded joints fail over time: intermittent contact, arcing, eventually a full outage.

Loss of warranty

Inadequate copper-aluminum joints do not meet the joint requirements specified by the equipment approval standards (IEC 61439, IEC 61238), which can void equipment warranty and raise liability questions.

How does CUPAL solve the problem?

CUPAL bimetal sheet contains both copper and aluminum simultaneously, cold-roll-bonded and diffusion-welded together inseparably. The solution addresses the galvanic corrosion problem on several levels:

1. Same metal contacts same metal

A CUPAL washer or transition element sits between the copper and aluminum conductors so that:

• the copper side faces the copper cable lug
• the aluminum side faces the aluminum busbar

The outer faces contact the same metal on both sides — no potential difference, no galvanic corrosion.

2. The transition zone is protected

The copper-aluminum interface lives inside the CUPAL sheet, where the diffusion weld ensures a permanent, hermetic connection. This transition zone never meets moisture, never grows an oxide layer, never starts the galvanic-corrosion process.

3. Low and stable contact resistance

CUPAL joint contact resistance stays low and stable over the equipment's lifetime, because the critical Cu/Al interface lives in a protected environment within the composite and never contacts moisture.

4. Long-term reliability

CUPAL is a proven, decades-validated material (langjährig bewährt). It is successfully used across Europe in energy-distribution systems, switchgear, lightning protection and renewable-energy installations.

Practical applications

CUPAL washers

The simplest and most common application: M6–M20 CUPAL washers placed between copper cable lugs and aluminum busbars. Installation takes minutes and immediately provides a protected, corrosion-free joint.

CUPAL strips

In lightning-protection systems and cable-lug joints, CUPAL strip is wrapped around the connection point to ensure a corrosion-free transition.

CUPAL transition plates

For larger contact areas (busbars, distribution-board rails), CUPAL transition plates provide uniform contact and full corrosion protection.

Prevention or after the fact?

Preventing galvanic corrosion is always cheaper and simpler than repairing it after the fact. A CUPAL washer costs a fraction of replacing a failed joint, refurbishing switchgear, or — worst case — covering damage from a fire.

Equipment and connector standards (DIN 43671 for busbars, IEC 61439 for low-voltage switchgear, IEC 61238 for cable connectors) set requirements on joints between dissimilar metals — contact resistance, temperature rise, long-term stability — that CUPAL transition elements can meet thanks to decades of proven use.

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