About STL



Guides and

Type Test


Inside STL
About STL


About STL



The Short-Circuit Testing Liaison (STL) provides a forum for voluntary international collaboration between testing organisations. The basic aim is the harmonised application of IEC and Regional Standards for the type testing of electrical power equipment.
Note: STL is concerned with high voltage electrical transmission and distribution power equipment (i.e. above 1000V a.c. and 1200V d.c.) for which the type tests specified in Standards include short-circuit and dielectric verification tests


- The objectives to which Members of STL have agreed are:
- The uniform interpretation of IEC and Regional Standards related to IEC Standards for the testing of electrical power equipment by the preparation of STL Guides.
- The uniform presentation of test results and data in the different documents issued by each testing organisation and the conditions on which each document can be issued.
- The adoption of a uniform front sheet for the Type Test Certificates issued by and under the responsibility of individual Members, indicating that the verification tests have been performed in accordance with the appropriate Standard and the agreed interpretations of the relevant STL Guide.
- The harmonisation of measuring techniques and methods to be used when performing the type
tests specified in the Standards.


Members of STL have agreed to co-operate in the preparation of Guides to provide harmonised interpretation of IEC and Regional Standards related to IEC Standards.
STL Guides will be published, given wide circulation, and made available to other testing organisations.
STL Guides will be made available to the appropriate standardisation bodies for consideration.
STL Guides will be revised when necessary particularly to reflect changes in Standards.
The Members of STL hope that non-member-testing organisations will also follow the procedures set out in STL Guides and would appreciate mention of the appropriate STL Guide in their test documents.


STL as a collaboration does not itself issue Certificates. Each STL Member testing organisation or laboratory issuing a Test Certificate is responsible for the validity and contents of that Certificate.
STL Members pledge that when testing for certification to a Standard in respect of which an STL Guide has been issued they will test only in accordance with the agreed interpretation of the Standard as given in the STL Guide.
In addition, STL Members have agreed to present Certificates in the form given in the STL General Guide.


The affairs of STL are directed and controlled by a Management Committee. Each Member organisation has one vote but may appoint more than one delegate to each meeting. Decisions at these meetings on general policy, preparation and publication of STL Guides and acceptance of new Members are taken by a 2/3 majority.
STL Guides are prepared by the STL Technical Committee set up by the Management Committee and comprising experts designated by member organisations with a Chairman appointed by the Management Committee. Each STL Member has the right to representation on the Technical Committee. New applicants to STL are normally requested to participate in the work of the Technical Committee for a period of time prior to admission as a Member of STL. The programme of work of the Technical Committee is decided by the Management Committee.
STL is not established for commercial purposes.
Members of STL shall inform customers and users of the agreed Objectives and Principles of Operation of STL.
No Member of STL shall make any public statement or issue printed publicity on the affairs of STL in relation to matters not approved by the STL Management Committee.