This standard deals with the requirements for auxiliary circuits mainly consisting of control circuits. This publication is the new stage of development of standard DIN VDE 0100-557 (VDE 0100-557):2007-06 which the German national committee had proposed to the IEC in 2007 as a new international standardization effort. The requirements given are to be considered in conjunction with those of the other standards of the series DIN VDE 0100 (VDE 0100). The following significant modifications have been made with respect to DIN VDE 0100-557 (VDE 0100-557):2007-07: a) new requirements for cross-circuit protection have been formulated; b) new functional performance requirements have been formulated; c) the layout has been editorially revised; d) additions to the Clause "Terms and definitions" have been incorporated; e) references have been updated. The responsible committee is DKE/UK 221.1 "Schutz gegen elektrischen Schlag" ("Protection against electric shock") of the DKE (German Commission for Electrical, Electronic and Informational Technologies) at DIN and VDE.