Upgrading Process Objects on Redundant CPU 410-5H - System Expansion Card Symmetry Rules

In a redundant SIMATIC PCS 7 CPU 410-5H (6ES7410-5HX08-0AB0) automation system, you cannot operate with asymmetric Process Object capacities between partner CPUs. Both controllers must possess identical System Expansion Card (SEC) sizing to maintain redundant coupling and synchronization. When upgrading Process Objects online using CPU 410 Expansion Packs (6ES7653-2CC00-0XB0), you must have two expansion licenses available—one for each physical CPU. If you attempt to upgrade only one controller, the system either aborts the redundant upgrade or disables fault-tolerant redundancy, restricting total plant capacity to the lower-licensed CPU.

Hardware Sizing and System Expansion Card (SEC) Principles

The SIMATIC PCS 7 CPU 410-5H controller (6ES7410-5HX08-0AB0) features a single unified hardware platform where operating memory and Process Object (PO) capacity are governed entirely by the plug-in System Expansion Card (SEC) inserted into the rear slot of the CPU.

In redundant architectures (AS 410-5H fault-tolerant pairs), two identical CPU 410-5H units synchronize continuously over fiber-optic sync modules (6ES7960-1AA06-0XA0). Each half-CPU must execute identical program structures in cycle-accurate lockstep.

The Mandatory SEC Symmetry Rule in Fault-Tolerant Systems

Siemens system architecture mandates strict System Expansion Card Symmetry across redundant partner controllers:

Both CPUs in a redundant pair must have the identical SEC PO rating (e.g. both 1000 PO or both 2000 PO).
The operating system cross-compares hardware capacity keys during redundant link-up.
If CPU A holds a 1000 PO SEC and CPU B holds an un-upgraded 500 PO SEC, the redundant operating state will reject synchronization, generating an event in the diagnostic buffer and preventing bumpless failover.
Even if the controller pair temporarily couples, the system enforces the lowest common denominator: total usable capacity is clamped to 500 PO, rendering the extra capacity on CPU A completely unusable.

Online PO Upgrade Workflow with CPU 410 Expansion Packs

In PCS 7 V8.1 and higher, PO expansion can be executed online in RUN without stopping the process using CPU 410 Expansion Packs (6ES7653-2CC00-0XB0):

Procure Dual Expansion Packs: Purchase two identical expansion packages to upgrade both CPUs simultaneously.
Load License Keys into ALM: Transfer the two PO license keys to the Engineering Station via Automation License Manager.
Execute Upgrade via PCS 7 Wizard:
- In SIMATIC Manager, select Target system > CPU 410-5H > Upgrade CPU 410....
- The upgrade wizard prompts for both controller target addresses and validates that both licenses are available.
- The wizard transfers the license to CPU 1, switches master/standby roles, and transfers the license to CPU 2, maintaining continuous plant operation without stopping the process.

Operational Consequences of Asymmetric SEC Capacities

Attempting to proceed with only a single expansion license creates serious operational risks in a live production environment:

If the primary CPU fails while holding 1000 PO, the standby CPU holding only 500 PO cannot accept the entire technological program, triggering an immediate shutdown of both controllers (complete plant STOP).
Siemens technical support explicitly classifies asymmetric SEC operation as an unreleased configuration.

Comparison of CPU 410 Upgrade Scenarios: Standalone vs Redundant

The table below contrasts upgrade requirements across controller topologies:

System ArchitectureExpansion Packs RequiredUpgrade ExecutionRedundant Failover During UpgradeSymmetry Rule EnforcedSingle AS 410-5H1 Expansion Pack (6ES7653-2CC00-0XB0)Online in RUNNot applicable (Single controller)No (Single SEC)Redundant AS 410-5H Pair2 Expansion Packs (1 per CPU)Online in RUN (Sequential)Bumpless master/standby switchoverStrict Symmetry MandatoryHardware SEC Swap (Legacy)2 Physical SEC CardsOffline (CPU STOP required)Sequential subrack de-energizationStrict Symmetry Mandatory

Verification

Verify SEC capacity symmetry and redundant synchronization:

In SIMATIC Manager, select the redundant AS station and open PLC > Diagnostic/Setting > Module Information.
Open the Performance tab for CPU 1; note the active Process Object capacity (e.g. 1000 PO).
Open the Performance tab for CPU 2; confirm the Process Object capacity matches CPU 1 exactly (1000 PO).
Check the CPU front LEDs: confirm RUN LED is solid green on both CPUs and REDF (Redundancy Fault) is off.
In the diagnostic buffer, confirm status Redundant mode established.

Limitations and Operational Precautions

Review the following commercial and operational precautions:

Commercial Procurement Guardrail: Upgrading a redundant AS 410 controller pair requires ordering TWO Expansion Pack licenses (6ES7653-2CC00-0XB0). Sizing controller PO capacity requires exact MLFBs verified against the Siemens Industry Mall.
Do Not Remove SEC Under Voltage: Never attempt to remove or insert a physical SEC card into a powered CPU rack.
Firmware Version Parity: Ensure both CPUs run the identical firmware release prior to executing online PO upgrades.

Engineer FAQ

Can I upgrade one CPU 410-5H now and upgrade the second one next month when budget is available?

No. In a redundant pair, operating with different SEC capacities is strictly unsupported. Both CPUs must have matching SEC ratings to synchronize and maintain bumpless redundancy. You must wait until both expansion licenses are procured.

Does upgrading POs online with CPU 410 Expansion Packs cause a process bump?

No. When executed via the PCS 7 CPU 410 Upgrade Wizard, the upgrade is performed sequentially across the redundant pair while the process continues running without interruption.

What happens if one CPU has a higher PO capacity than its partner?

The system either rejects redundant coupling entirely or clamps total usable program capacity to the lower-rated CPU, generating persistent redundancy diagnostic faults.