BS EN 50588-3:2018 Medium power transformers 50 Hz, with highest voltage for equipment not exceeding 36 kV Transformers with cable boxes on the high-voltage and/or low-voltage side. Cable boxes type 1 for use on transformers meeting the requirements of EN 50588-2

Rated frequencies
Electrical insulation
Distribution transformers
Electrically-insulated bushings
Electrical impedance
High-voltage equipment
Power transformers
Sound intensity
Three-phase transformers
Rated power
Oil-immersed transformers
Short-circuit currents
Alternating-current transformers
Rated voltage

Link: BS EN 50588-3:2018 Medium power transformers 50 Hz, with highest voltage for equipment not exceeding 36 kV Transformers with cable boxes on the high-voltage and/or low-voltage side. Cable boxes type 1 for use on transformers meeting the requirements of EN 50588-2
Source: BSI Standards