Merging Multiproject Subnets in SIMATIC PCS 7 to Connect Engineering Station to Plant Bus

In SIMATIC PCS 7, Industrial Ethernet subnets created within individual subprojects of a multiproject remain logically isolated local subnets until merged. If an Engineering Station (ES) or Operator Station (OS) cannot connect to the Plant Bus configured in an Automation System (AS) subproject, right-click the Multiproject root in SIMATIC Manager, select 'Multiproject -> Adjust Projects...', navigate to the 'Merge/Split Subnets' tab, select 'Industrial Ethernet', and click 'Execute...'. In the dialog, combine the local subnets (e.g., Plantbus_AS, Plantbus_ES, Plantbus_OS) into a single global multiproject subnet. Once merged, open NetPro to attach all station network adapters (CP 1623 or IE General) to the unified Plant Bus and configure S7 Named Connections.

Executive Summary

When creating large-scale SIMATIC PCS 7 architectures with distributed subprojects (e.g., dedicated AS, OS, ES projects, and a Master Data Library), engineers often discover that the Engineering Station cannot establish communication with the AS controller or browse its Plant Bus in NetPro. This occurs because subnets created within isolated subproject hardware configurations default to local network scopes. Attempting to assign cross-project connections without adjusting multiproject subnets fails. This article provides the definitive engineering procedure to merge Industrial Ethernet subnets across PCS 7 subprojects, configure global plant buses, and establish S7 Named Connections.

Architecture and Fundamental Mechanics

The SIMATIC Manager Multiproject structure modularizes extensive engineering databases into manageable subprojects. In HW Config, network interfaces (such as CP 443-1, CPU 410-5H internal PN-X5 interfaces, CP 1623, or standard network cards) must be attached to an Industrial Ethernet subnet.

When created locally, each subproject maintains an independent subnet object table within its local database. Even if two subnets share identical names (e.g., 'Plant Bus'), they possess distinct internal GUIDs and cannot route cross-station S7 communication.

Executing 'Adjust Projects -> Merge/Split Subnets' scans the multiproject database, unifies disparate local Industrial Ethernet identifiers into a single multiproject-wide subnet object, and synchronizes NetPro connection tables. Once merged, cross-project routing, S7 Named Connections between WinCC Applications and CPU 410 controllers, and centralized ES downloads operate seamlessly across the shared physical Ethernet infrastructure.

Step-by-Step Implementation Procedure

Standardize Subnet Configurations in Subprojects:
a. Open the AS subproject in SIMATIC Manager, launch HW Config, and verify the controller network interface (PN-X5 or CP 443-1) is attached to an Ethernet subnet named 'Plantbus_AS'.
b. Open the ES subproject HW Config, verify the PC station communications processor (CP 1623 or IE General) is attached to an Ethernet subnet named 'Plantbus_ES'.
c. Open the OS subproject HW Config and verify station adapters are attached to 'Plantbus_OS'.
Execute Multiproject Subnet Merge:
a. In SIMATIC Manager, select the root Multiproject folder in Component View or Plant View.
b. Right-click and choose 'Multiproject -> Adjust Projects...'.
c. Switch to the 'Merge/Split Subnets' tab.
d. Under 'Subnet type', select 'Industrial Ethernet' and click the 'Execute...' button.
e. In the 'Merge Subnets' dialog, select 'Plantbus_AS', 'Plantbus_ES', and 'Plantbus_OS', then click 'Merge'. Assign a global name such as 'PlantBus_Global' and click 'OK'.
Verify Connections in NetPro:
a. In SIMATIC Manager, open NetPro from the Multiproject root.
b. Verify that all stations (AS, ES, OS servers) are visually connected to the single thick green Industrial Ethernet line representing the global Plant Bus.
c. Highlight the ES WinCC Application or STEP 7 connection table, insert a new S7 Connection targeting the CPU 410-5H, and set the connection type to 'Named Connection'.
d. Execute 'Network -> Save and Compile' in NetPro to ensure zero routing or addressing errors.
Download Station Configurations:
a. In NetPro, select each station and download network configurations to the local Station Configuration Editor (SCE) and AS controllers.

Verification

In NetPro, verify that 'Save and Compile' completes with 0 errors and 0 warnings.
From the Engineering Station, open a command prompt and ping the IP addresses of the CPU 410-5H PN interfaces and OS server adapters across the Plant Bus.
Open SIMATIC Manager, highlight the AS S7 Program, and execute 'PLC -> Diagnostic Buffer' to confirm online connectivity from the ES.
Open the WinCC Explorer on the ES, run Channel Diagnosis, and verify S7 Named Connections display a healthy 'OK' state with active telegram exchanges.

Limitations and Operational Precautions

Merging subnets requires exclusive access to the multiproject database; ensure all engineering team members close HW Config, NetPro, and CFC editors before executing the merge. Never delete a merged subnet directly from a single subproject, as this breaks cross-project references and necessitates re-merging. If IP address or subnet mask overlaps exist between subprojects, NetPro compilation will abort until IP uniqueness is resolved.

Engineer FAQ

Why did my AS Plant Bus disappear from the merged section after clicking OK?

If an individual subproject was locked by an open editor during the merge operation, or if duplicate subnet properties collided, the merge transaction rolled back. Close all subproject windows and re-run Adjust Projects.

Can I merge PROFINET IO fieldbuses using Adjust Projects?

No. Adjust Projects is designed for Plant Bus and Terminal Bus Industrial Ethernet subnets. Field-level PROFINET IO networks (connecting ET 200SP HA remote I/O) are local to their specific CPU controller and must not be merged across controllers.

Do I need separate physical network cards for Plant Bus and Terminal Bus?

Yes. Industrial best practice and Siemens PCS 7 security architectures mandate physically separated subnets: Plant Bus (connecting AS, OS servers, and ES) and Terminal Bus (connecting OS servers, OS clients, and engineering stations).

Does merging subnets change existing IP addresses?

No. Merging subnets harmonizes logical network objects in the engineering database without modifying configured IP addresses or MAC addresses.

What happens if I split a merged subnet later?

Splitting subnets breaks all cross-project S7 connections in NetPro, causing OS compilation and runtime tag communication to fail until connections are re-established.