This part of EN 50123 specifies requirements for outdoor d.c. switch-disconnectors, disconnectors and earthing switches for use in outdoor fixed installations of traction systems. NOTE 1 EN 50121-5 specifies requirements for electromagnetic compatibility (EMC). NOTE 2 In this document the word ""unit"" means ""switch-disconnector and/or disconnector and/or earthing switch"" as defined in 3.1.4, 3.1.5 and 3.1.6 of EN 50123-1.