This standard specifies the requirements for the Terminal Block Assemblies intended for checking and changing the energy measuring devices, both for Low and High Voltage supplies. Such units are also known as Test Block Units (TBUs) and are intended to be fitted and connected between transformers and the measuring equipment, where indirect or semi-direct measuring is involved, and between the feeding installation and the individual outgoing connection, where direct measuring is involved. It applies to Test Block Units intended to connect round copper conductors with or without a special preparation, having a cross section between 1,5 mm² and 35 mm², intended to be used in circuits of a rated voltage not exceeding 400 V a.c. up to 1000 Hz. This standard can also be used as a guide for Test Block Units as intended for checking protection equipment.