EN IEC 61394 Overhead Lines - Grease Requirements for Aluminum, Aluminum Alloy and Steel Bare Conductors

The standard “EN IEC 61394 Overhead lines - Grease requirements for aluminum, aluminum alloy and steel bare conductors”, developed by the International Electrotechnical Commission (IEC) and later published as a European standard as part of harmonization efforts, describes the requirements and test methods for greases designed to protect exposed overhead conductors from corrosion.

This standard includes requirements and test methods for greases (or similar compounds) specifically designed to provide corrosion protection for bare overhead conductors used in electrical transmission and distribution lines. These conductors typically consist of:

• Aluminum wires
• Aluminum alloy wires
• Steel wires (galvanized/zinc coated or aluminum coated)
• Or combinations of these.

Bare overhead conductors are exposed to harsh environmental conditions (rain, humidity, salt spray, industrial pollution, extreme temperatures) that can cause galvanic corrosion, especially between different metals. Greases help by filling the gaps between the wires, creating a barrier against moisture and oxygen, and remaining stable throughout the conductor's lifespan (including manufacturing, storage, installation, and operation under normal and short-circuit conditions).

The lubricant should have the following properties:

• It must provide protection against atmospheric corrosion.
• It must adhere well to the wires.
• It should not leak, drip, or deteriorate at high operating temperatures.
• The short circuit must remain effective during heating events.
• It should not damage conductive materials or increase corona noise.
• It must comply with health and safety requirements.

This standard defines two main product types:

• Products applied in a cold state (e.g., typical greases, usually thixotropic or semi-solid)
• Products applied while hot (e.g., petrolatum-based compounds)

The key performance aspects covered are:

• Dropping point (the temperature at which grease becomes liquid)
• Penetration/consistency (how hard or soft the grease is)
• Low temperature adhesion
• High temperature stability
• Aging resistance
• Corrosion protection (tested on relevant metal samples)
• Stability of the conductor under high temperature and short circuit conditions.
• Acidity or alkalinity (especially for certain types)

Tests are divided into two groups: type tests (for qualification/approval) and sample/routine tests (for quality control during production).

In general, the characteristic features of the tests are as follows:

• Sample preconditioning
• Drop point (ISO-based methods)
• Permeability / conical penetration
• Low temperature adhesion
• Aging (through preconditioning and exposure)
• Corrosion tests (typically using salt spray or similar)
• High-temperature stability in conductive samples.
• Stability under short-circuit conditions (in complete conductor samples)

The annexes to this standard provide detailed normative procedures for specific tests (e.g., acidity/alkalinity method, aging preparation, high temperature and short-circuit stability).

In overhead line design and maintenance, using a grease conforming to the EN IEC 61394 standard helps extend the service life of the conductor, especially in coastal, industrial, or contaminated areas where corrosion accelerates deterioration. Many conductor manufacturers and electricity distribution companies refer to this standard when specifying lubrication requirements for aluminum conductors, steel-reinforced conductors, or similar conductor types.

The EN IEC 61394 standard is necessary because bare overhead conductors, the most common type being aluminum conductors with steel reinforcement, especially in high-voltage transmission and distribution lines, face significant corrosion risks under real-world service conditions. Without standardized, reliable grease protection that meets this standard, conductors can prematurely degrade, leading to shortened service life, mechanical failures, increased maintenance costs, and even downtime or safety hazards.

Bare overhead conductors operate for decades (typically a design life of 40-60 years) exposed to the atmosphere and face the following:

• Atmospheric humidity, rain, moisture (water penetrates beach crevices).
• Pollutants (industrial emissions, acid rain, dust).
• Saltwater spray/marine aerosols (particularly intense in coastal or offshore areas).
• Galvanic corrosion (aluminum conductive steel-reinforced wires come into contact with a galvanized steel core, aluminum acts as the anode, and corrodes primarily when an electrolyte (moisture + salts) is present).
• Friction and abrasion (wind vibration, rapid movement, and wind-induced motion cause micro-movements between the wires, cracking protective oxide layers or zinc coatings and accelerating corrosion).
• Temperature cycling (daily or seasonal variations and heating from load currents, if not appropriate, promotes moisture ingress and grease degradation).

Under extreme conditions (e.g., in heavily polluted or marine environments), unshielded or inadequately shielded aluminum conductors with steel reinforcement have shown significant corrosion in as little as 5-10 years. Pitting in the aluminum, rusting of the steel core, loss of mechanical strength, and ultimately wire fractures or core failure have occurred.

Grease fills the gaps between the wires during production, creating the following physical barrier:

• It keeps out moisture and oxygen (preventing oxidation and galvanic effects).
• It provides protection during storage, transport, and cable laying (before the lines are energized).
• It remains effective for a long time (continuously up to 70-90 degrees at operating temperatures, even higher during overload/short circuits).
• It reduces friction damage (by lubricating the wire interfaces).
• It does not promote corona formation or increase radio interference.

However, not all greases perform the same. Some melt and leak at high temperatures, while others crack, dry out, or become acidic/alkaline. Poor greases can trap moisture or degrade under short-circuit heating.

In short, the EN IEC 61394 standard is a practical safety measure to prevent one of the leading causes of overhead line conductor failure and premature replacement.

For many years, our organization, with its competent and experienced staff, has been understanding the needs of its clients, providing the advanced testing services they require, and assisting them in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services compliant with the EN IEC 61394 standard.