IEC 60120: String Insulator Ball-Socket Couplings — The Critical Link in Overhead Lines

String Insulator Ball-Socket Couplings — A 500 kV Line Is Strung Together by Tens of Thousands of “Balls”

IEC 60120 specifies ball and socket coupling dimensions for string insulator units. Overhead line insulator strings consist of dozens of cap-and-pin insulators connected by ball-socket couplings — connections that must be both flexible (accommodating conductor swing and vibration) and absolutely reliable (a single disconnection scatters the entire string).

Standardization core: Standard ball diameters and socket bore dimensions (typical ball sizes: 16/20/24/28/32 mm) ensure interchangeability across manufacturers. Each socket contains a locking pin (split pin or W-clip) — the smallest component in the insulator string, carrying the greatest safety responsibility.