IEC 62640:2011 applies to residual current-operated devices (RCD) incorporated in, or specifically intended for use with two pole socket-outlets, with or without earthing contact for household and similar uses (SRCD: socket-outlet residual current devices). SRCDs, according to this standard, are intended to be used in single phase systems such as phase to neutral or phase to phase or phase to earthed middle conductor. SRCDs are only intended to provide additional protection downstream of the SRCD. SRCDs are intended for use in circuits where the fault protection (indirect contact protection) is already assured upstream of the SRCD.