Understanding IEC 60840 for Cable Accessories

In the world of high-voltage power cables, reliability is everything. A single failure can cause widespread outages, costly repairs, and even safety hazards. That is why international standards exist—to ensure that cables and their accessories are designed, tested, and proven to perform safely over decades of service. Among these standards, IEC 60840 stands as one of the most important for high-voltage cable systems.

1. What Is IEC 60840?

IEC 60840 is an international standard that specifies test methods and requirements for power cable systems—including cables alone and accessories alone—for fixed installations. It is published by the International Electrotechnical Commission (IEC), the global organization that sets standards for electrical and electronic technologies.

The standard covers rated voltages above 30 kV (Um = 36 kV) up to and including 150 kV (Um = 170 kV). In simpler terms, it applies to the "high-voltage" range of power cables—the kind used to transmit electricity over long distances between cities, from power plants to substations, and within large industrial complexes.

What does the voltage notation mean?

• U = rated voltage (the normal operating voltage)

• Um = maximum system voltage (the highest voltage the system can sustain)

So when IEC 60840 says "above 30 kV up to 150 kV," it is referring to cables that operate in this critical voltage range—the backbone of modern power transmission.

2. What Does the Standard Cover?

IEC 60840 applies to single-core cables and individually screened three-core cables, as well as their accessories. The accessories covered include:

• Cable joints (straight joints, transition joints between different cable types—though not between extruded and paper-insulated cables)

• Terminations (both indoor and outdoor types)

• Other connecting devices used in cable systems

However, the standard does not cover special cables such as submarine cables, which may require modifications to the standard tests or entirely different test conditions. It also excludes transition joints between extruded insulation cables and paper-insulated cables.

3. The Testing Framework: Three Levels of Assurance

IEC 60840 establishes a comprehensive testing framework with three distinct levels:

A. Type Tests
Type tests are performed on a small number of samples to verify that the design and manufacturing process can produce accessories that meet all performance requirements. These are the most demanding tests, covering electrical, mechanical, thermal, and environmental performance.

For accessories, type tests include:

• Partial discharge measurement—to detect microscopic discharges within voids or at interfaces

• Power frequency withstand voltage tests—to verify insulation strength under operating conditions

• Lightning impulse voltage tests—to simulate surge events

• Heating cycle voltage tests—to verify thermal performance under load

• Bending tests—to verify mechanical flexibility

• Water penetration tests—to verify sealing integrity

B. Sample Tests
Sample tests (also called acceptance tests) are performed periodically on random samples taken from production batches. They verify that the factory can consistently reproduce the quality established during type testing. These typically include a subset of the type test sequence—partial discharge measurement, withstand voltage tests, and dimensional checks.

C. Routine Tests
Routine tests are performed on every single accessory before it leaves the factory. These are relatively quick but essential for catching individual manufacturing defects:

• Visual inspection

• Partial discharge measurement

• Power frequency withstand voltage test

• Dimensional verification

• Material property checks

4. The Prequalification Test: The Ultimate Trial

For cables with high electrical stress—specifically, those with a calculated nominal conductor electric stress above 8.0 kV/mm or a nominal insulation electric stress above 4.0 kV/mm—IEC 60840 requires a prequalification test.

The prequalification test is not a factory test but a long-term field trial. After successful type testing, the complete cable system (cable plus accessories) is installed outdoors under realistic conditions. A voltage of 1.7 U₀ is applied, and 180 heating cycles are performed over the course of a year.

This test ensures that the cable system can withstand decades of real-world operation before it is approved for commercial installation.

5. What's New in the 2020 Edition?

The latest edition of IEC 60840—Edition 5.0, published in 2020—introduced several significant technical changes:

These changes reflect the evolving demands of the industry—greater focus on fire safety, environmental performance, and compatibility with modern switchgear technologies.

6. How IEC 60840 Relates to Other Standards

IEC 60840 is part of a family of standards for extruded insulation cables:

IEC 62067 has been aligned with IEC 60840, but with one key difference: IEC 62067 recognizes only high-stressed cable designs and therefore exclusively accepts testing on a system basis (cable plus accessories together), whereas IEC 60840 differentiates between high-stressed and normal-stressed designs.

7. Why IEC 60840 Matters

For manufacturers, IEC 60840 provides a clear, internationally recognized framework for designing and testing cable accessories. Passing the tests required by the standard is essential for gaining market access in most countries.

For utilities and project developers, specifying accessories that comply with IEC 60840 provides assurance of quality and reliability. It means the accessories have been rigorously tested—not just once, but through type, sample, and routine testing—to verify their performance under electrical, thermal, mechanical, and environmental stress.

For engineers and installers, understanding IEC 60840 helps in selecting the right accessories, interpreting test reports, and ensuring that installations meet the required standards.

8. A Standard That Evolves with the Industry

IEC 60840 is not static. It has evolved through multiple editions—from the first edition in 1988 (which covered only cables) to the second in 1999 (which added accessories), through editions in 2004, 2011, and the current 2020 edition.

Amendments continue to refine the standard. Amendment 1 (2023) updated terminology, test procedures, and requirements, and aligned specific tests with related IEC documents. A corrigendum followed in 2025.

This continuous evolution ensures that IEC 60840 remains relevant to the latest technologies—from fire-resistant materials to SF₆-free switchgear—and continues to provide the assurance that the industry depends on.

IEC 60840 is the backbone of quality assurance for high-voltage cable accessories in the 30 kV to 150 kV range. It establishes a comprehensive testing regime—type, sample, routine, and prequalification—that verifies the performance of accessories before they are installed in the field. By specifying test methods for electrical, thermal, mechanical, and environmental performance, the standard ensures that the accessories we rely on to keep the power flowing are designed and manufactured to last—often for decades—in some of the most demanding conditions imaginable.

Whether you are a manufacturer, a utility engineer, or a project developer, understanding IEC 60840 is essential for ensuring that the cable accessories you specify, install, or maintain meet the highest standards of safety and reliability.