MT 21 - TC 36/MT 21

IEC 60120:2020 define the dimensions of a series of standard ball and socket couplings using the standard locking devices (see IEC 60372) in order to permit the assembly of insulators or metal fittings supplied by different manufacturers. This document applies to string insulator units of the cap and pin and long rod types and their associated metal fittings. For the pin ball and the socket, dimensions apply to the finished product after any surface treatment. Extreme positions of the pin ball in the socket are given in annex. Typical examples of gauges for checking the dimensions of pin balls and sockets are given in annex.

IEC 60372:2020 is applicable to locking devices used with ball and socket couplings of string insulator units and used with the corresponding metal fittings standardized in IEC 60120, when they are supplied separately.The object of this document is
- to define the shapes and some standard dimensions for locking devices,
- to define the test methods for locking devices,
- to state the acceptance conditions for supply,
- to give other dimensions for guidance of manufacturing only.
This fourth edition cancels and replaces the third edition published in 1984. This edition includes the following significant technical changes with respect to the previous edition:
a. Two new designated size of couplings, 36 and 40, were introduced;
b. the relevant content of the 28B W-clip was deleted;
c. Annex A is informative, Annex B is normative, Annex C is informative.

IEC 60471:2020 applies to string insulator units of the cap and pin type and also of the long rod type as well as the fittings used with such insulators. The object of this document is to define the dimensions of a series of clevis and tongue couplings to permit the assembly of insulators or fittings supplied by different manufacturers.
This third edition cancels and replaces the second edition published in 1977. This edition includes the following significant technical changes with respect to the previous edition:
- there are no new clevis and tongue couplings;
- For the dimensions of the existing designated size of couplings that characterize the same location, the effective number of the size is unified.