The subracks form the basic mechanical framework of the SIMATIC S7-400. Their functions are as follows:

• Mechanical fixing of the modules
• Supplying the modules with the operating voltages
• Connecting the individual modules over the backplane bus

The subracks are designed for wall mounting and installation in frames and cabinets

Various subracks are available for setting up the SIMATIC S7-400.

UR1 (Universal Rack)

• For setting up central controllers and expansion units
• For holding up to 18 modules
• Also suitable for S7-400H
• Also available as aluminum rack

UR2 (Universal Rack)

• For setting up central controllers and expansion units
• For holding up to 9 modules
• Also suitable for S7-400H
• Also available as aluminum rack

CR2 (Central Rack)

• For setting up central controllers
• For holding up to 18 modules
• Segmented rack:
  For operating two mutually independent S7-400 CPUs without S7-400 Multicomputing, but with communication between the CPUs over the backplane bus (C bus). Both CPUs can address their own local I/O modules (segmented P bus).

CR3 (Central Rack)

• For configuring central racks
• Optimized for distributed automation solutions due to holding up to 4 modules

UR2-H

• For configuring a complete S7-400H system in one subrack
• Also suitable for S7-400:
  Operation of 2 separate CPUs with their own I/O (separate P and C buses)
• Can also be used as an expansion unit
• For holding up to 18 modules
• Also available as aluminum rack

ER1 (Extension Rack)

• For setting up expansion units economically
• For holding up to 18 modules with restricted functionality
• Also suitable for S7-400H
• Also available as aluminum rack

ER2 (Extension Rack)

• For setting up expansion units economically
• For holding up to 9 modules with restricted functionality
• Also suitable for S7-400H
• Also available as aluminum rack