1. ETS 300 253(1995).European Telecommunication Standard Equipment Engineering (EE); Earthing and Bonding of Telecommunication Equipment in Telecommunication Centers January 1995.
2. IEC 60417(2004).Graphical Symbols for Use on Equipment June 2004.
3. IEC 60204(2018).Safety of Machinery – Electrical Equipment of Machines – Part 1: General Requirements– Part 1 2018.