Siemens S7-400 Rules for Connection, Type of Connection Maximum Total Cable Length

Installing the S7-400

Rules for Connection

When you connect a central rack to expansion racks, you must observe the following rules:

•You can connect up to 21 ERs of the S7-400 to one CR.

•The ERs are assigned numbers to identify them. The rack number must be set on the coding switch of the receive IM. Any rack number between 1 and 21 may be assigned. Numbers must not be duplicated.

•You may insert up to six send IMs in one CR. However, only two send IMs with 5 V transfer are allowed in one CR.

•Each chain connected to the interface of a send IM can comprise up to four ERs (without 5 V transfer) or one ER (with 5 V transfer).

•The exchange of data via the communication bus is limited to 7 racks, meaning the CR and ER numbers 1 to 6.

•The maximum (total) cable lengths specified for the type of connection must not be exceeded.

Type of Connection	Maximum (Total) Cable Length
Local connection with 5 V transfer via	1.5 m
IM 460-1 and IM 461-1
Local connection without 5 V transfer via	5 m
IM 460-0 and IM 461-0
Remote connection via IM 460-3 and	102.25 m
IM 461-3
Remote connection via IM 460-4 and	605 m
IM 461-4

Automation System S7-400	Hardware and Installation	2-5
A5E00850741-01