Cable lugs & crimp connections — requirements for compression connectors (IEC 61238-1)

A cable connection is rarely stronger than its weakest joint — a poorly executed cable lug or crimp connection can form a local hotspot that eventually leads to an arc-fault (see also the arc-fault guide and the thermographic-inspection guide, which is often used to detect such hotspots). IEC 61238-1 sets out the test and performance requirements for compression and mechanical connections for power cables.

What the standard governs

IEC 61238-1 (part 1: test methods and requirements) applies to compression and mechanical connectors for power cables with copper or aluminium conductors, in accordance with the cross-sections from IEC 60228. Among other things, the standard describes:

• Electrical requirements: the contact resistance of the connection must be low enough that the connection does not become hotter than the conductor itself under normal operating conditions — in practice this requires that the electrically effective cross-sectional area of the crimp is everywhere larger than that of the conductor.
• Mechanical requirements: tensile strength of the connection.
• Environmental/durability tests: including thermal-cycling tests to verify the long-term stability of the contact resistance.

Note: the exact contact-resistance limit value and the precise test regime are conductor-cross-section- and type-specific and follow from the manufacturer's classification in accordance with IEC 61238-1 — this article provides the standard's framework, not a universal resistance value.

Copper-aluminium: galvanic corrosion

When directly connecting a copper and an aluminium conductor (for example when connecting an aluminium supply cable to copper equipment terminals), there is a risk of galvanic corrosion: in the presence of moisture, the two dissimilar metals form an electrochemical couple, in which the aluminium gradually corrodes. This increases the contact resistance of the connection over time — a creeping problem that only becomes visible when there is a fault or during a thermographic inspection.

The common solution is a bimetallic cable lug (copper on the equipment side, aluminium on the cable side, mechanically/metallurgically joined within the lug itself) instead of a direct copper-aluminium clamped connection.

Practical relevance

When extending cabling in a company hall or cultivation operation — particularly for heavier supply cables where aluminium is used for weight/cost reasons — the choice of the correct cable-lug type (copper, aluminium, or bimetallic) directly affects the long-term reliability of the connection. An incorrectly chosen cable lug is often indistinguishable to the naked eye from a correct one; the manufacturer's specification and the right crimping tool (with matching die) are decisive here.

Common mistakes

1. Crimping a copper cable lug directly onto an aluminium conductor (or vice versa) without a bimetallic version — risk of galvanic corrosion and a gradually rising contact resistance.
2. Using the wrong crimping die or crimping force relative to the manufacturer's specification for the cable lug — this cannot guarantee the required contact resistance, even if the crimp looks visually correct.
3. Never periodically checking crimp connections thermographically — a deteriorating connection often first manifests as a local temperature rise, well before a visible fault occurs.

Related

• Thermographic inspection
• Arc flash — risks and control measures