Provides specifications applicable to the following types of transformers for use in resistance welding equipment: - single-phase transformers for a.c. welding, typically operating at 50 Hz or 60 Hz; - single-phase transformers with connected rectifier for d.c. welding, typically operating at 50 Hz or 60 Hz; - single-phase inverter transformers with connected rectifier for d.c. welding, typically operating at 400 Hz to 2 kHz; - three-phase transformers with connected rectifier for d.c. welding, typically operating at 50 Hz or 60 Hz.