Stranding class of the conductor is important in copper cable lug selection because it influences directly the fit, electrical performance, and mechanical reliability of the connection. Here's why:
Physical Fitness: Fine-stranded conductors like those of Class 5 and Class 6 according to DIN 57295/EN 60228 contain more overall diameter than fine-stranded or solid conductors of the same area. Socket lugs for solid or coarse-stranded wires might not fit all of the strands of a fine-stranded conductor, resulting in incomplete insertion or loose strands, which can weaken the connection.
Electrical Performance: When the lug is not specially made for the stranding class, improper contact is made by some strands, resulting in resistance increase and overheating or energy loss. Matching lugs that are properly designed ensure all the strands are tightly crimped to ensure maximum conductivity.
Mechanical Strength: Incorrect lug type will lead to unsatisfactory mechanical retention. The mechanical set-screw lugs, for instance, are not usually compatible with fine-stranded conductors since the screws may cut the strands. Compression lugs for flexible conductors (usually with a flared entrance and bigger barrel) provide a tight, vibration-resistant connection.
Safety and Compliance: Most standards and manufacturers also detail the approved types of lug for each conductor class. Installing an inappropriate lug can compromise safety standards and cause premature failure or dangerous situations.
In short:
Always choose lugs that are designed and rated to the conductor's stranding class to guarantee accurate fit, dependable electrical contact, mechanical soundness, and conformity to safety standards.