Siemens SIMATIC NET TeleControl SINAUT ST7 System Manual page 184

Installation and commissioning of the modems and routers
5.6 LTOP line transformer with overvoltage protection
Attachment to a 2-wire end point
2-wire end point over an LTOP 1 2-wire end point over an LTOP2
Attachment with a 4-wire end point or 2 x 2-wire end point
4-wire end point over an LTOP2 2 x 2-wire end point over an LTOP2
SINAUT ST7 station control system
184
System Manual, 09/2016, C79000-G8976-C178-10