WinCC V7.4 Redundancy Hardware Selection with S7-400H PLC and CP1623

Overview

Designing a redundant WinCC V7.4 SCADA system in front of a SIMATIC S7-400H requires more than duplicating servers. Every layer — server, network adapter, license, switch — has its own redundancy model, and the parts must be ordered in a specific combination. A common design error is to specify the wrong S7 communication license (SOFTNET instead of HARDNET, or a missing REDCONNECT upgrade) when the workstation hosts a CP1623 PCIe Ethernet card. This reference consolidates the correct part topology, compares two agent proposals, and documents the license logic you must verify before issuing a purchase order.

The target architecture assumed in this article is a 2-server / 2-client WinCC V7.4 SP1 SCADA cluster with redundant S7-400H PLCs and one or two SCALANCE switches forming the PROFINET/S7 backbone. All WinCC V7.4 server licenses are 6AV6371-1CA07-4AX0; all RT client licenses are 6AV6381-2CA07-4AX0; the WinCC Redundancy package is 6AV6371-1CF07-4AX0. PowerTags are bounded by RC 2048 (6AV6381-2BP07-4AX0).

WinCC V7.4 Redundancy Architecture Fundamentals

WinCC V7.4 redundancy works as an active/standby server pair that shares a project and an internal redundancy tag structure. Each server independently holds a complete image of the process database. After every configurable update cycle, the standby server compares its internal process image to the partner server. If the partner fails to respond within the configured timeout (default 25 s, settable 5–65535 s in WinCC Explorer under Computer Properties > Redundancy), the standby takes ownership of the WinCC clients and alarms.

The redundancy handshake is implemented at the WinCC application layer (TCP port 6677 for the Redundancy Synchronization service by default), not at the S7 layer. This is critical: the S7 communication itself can fail over inside a single PC if the workstation has two CP1623 cards, but the WinCC redundancy peer check is independent of which CP is used.

For a redundant S7-400H PLC, the CP1623 on the WinCC side must use the S7-REDCONNECT protocol extension to subscribe to both H-CPUs simultaneously and tolerate a CPU switch-over. This extension is licensed separately from the base HARDNET-IE S7 license.

Required software layers per WinCC server

1. Windows Server 2012 R2 / 2016 / 2019 (x64) — see WinCC V7.4 installation prerequisites in the SIMATIC WinCC V7.4 SP1 release notes.
2. SIMATIC WinCC V7.4 SP1 (RT 2048) — 6AV6371-1CA07-4AX0.
3. WinCC/Redundancy — 6AV6371-1CF07-4AX0 (one license per server, one floating license for the package itself).
4. SIMATIC NET PC software containing HARDNET-IE S7 — installed once and bound to the CP1623 hardware.
5. S7-REDCONNECT license — either as a stand-alone or as a Power Pack upgrade on top of HARDNET-IE S7.

HARDNET vs SOFTNET License Topology

Siemens S7 PC communication licenses are split into two families, and the choice is dictated entirely by the physical network adapter in the PC, not by the controller on the other end.

The decisive line in the catalog: HARDNET-IE S7 REDCONNECT (e.g. 6GK1716-0HB13-0AA0) is the correct license for a CP1623-equipped WinCC server front-ending an S7-400H. The Power Pack variant 6GK1716-0HB13-0AC0 upgrades an existing HARDNET-IE S7 license to REDCONNECT capability in place.

CP1623 Hardware Reference

The CP1623 (6GK1162-3AA00) is a PCIe x1 Ethernet card for SIMATIC PCs and supports PROFINET IO controller/IO device plus S7 / open communication. For a WinCC redundancy server, the relevant features are:

On a single physical CP1623 the integrated 2-port switch can be used either as an external MRP ring member (one port to the ring, one port free) or as a single direct connection. For redundancy to a S7-400H, only one CP1623 per server is sufficient from a pure protocol standpoint — both H-CPUs are reached through the same S7-REDCONNECT connection that internally handles the H-switchover.

Configuration Comparison: Original Agent Proposals

The original design phase produced two competing bills of material. Both used the same server and client licensing, but diverged on the PC-side communication license line and on the CP1623 count.

Configuration 1 fails because line item 2 specifies a SOFTNET license while the PC uses a HARDNET-class CP1623. SOFTNET-IE S7 REDCONNECT VM binds to a virtual adapter inside the OS, not to a CP1623 MAC/serial, so when SIMATIC NET starts it cannot find a matching license for the CP1623 and the S7 connection fails with licensing error.

Configuration 2 fails because line item 2b supplies the correct HARDNET base license but does not include the REDCONNECT upgrade. The server can talk to a non-redundant S7-400 but cannot track H-CPU switchover; alarms freeze after the first failover.

Corrected Bill of Materials

The corrected BoM uses one CP1623 per server, one HARDNET-IE S7 REDCONNECT license per server, and two SCALANCE switches in MRP. This is the minimum configuration that achieves both server-side and network-side redundancy without single points of failure.

How Many CP1623 Cards per Server?

The original Config 1 specified two CP1623 per server. This is technically valid but almost never necessary when the entire server is already redundant.

If dual CP1623 per server is chosen, the two cards must be on different PCIe buses (avoid shared upstream link) and the S7 connections must be split in WinCC so that primary variables are read through CP A and redundant variables through CP B. Otherwise both CPs will fail together on the same PCIe root complex fault.

SCALANCE Switch Selection and Network Redundancy

A single SCALANCE switch between the S7-400H and the two WinCC servers is the most common single point of failure in the proposed architecture. If that switch fails, both servers lose their S7 connections simultaneously and the entire HMI cluster goes dark — server redundancy cannot compensate because both servers are equally blind.

The minimum acceptable switch topology is two SCALANCE units configured as an MRP ring. Each WinCC server connects one CP1623 port to SCALANCE-A and the second port to SCALANCE-B. Each S7-400H CPU (H-CPU1 and H-CPU2) likewise connects to both switches through its PROFINET ports. The S7-REDCONNECT license tolerates one switch segment failure, the WinCC redundancy tolerates one server failure, and the union of the two tolerates any single hardware loss except simultaneous dual-server-plus-switch failure.

Logical Topology (Server, Switch, PLC)

The connection map below summarizes the validated topology. Each S7-400H CPU has its own PROFINET interface module (e.g. CP443-1) and is reachable through both SCALANCE switches. Each WinCC server has a single CP1623 with both ports connected to different SCALANCE units. WinCC redundancy peer traffic uses the same network but is logically separated by IP subnet and TCP port.

+-------------------+              +-------------------+
|   WinCC Server A  |              |   WinCC Server B  |
|   WinCC V7.4 SP1  |              |   WinCC V7.4 SP1  |
|   CP1623 [p1]-----+-------+      +----- CP1623 [p1]  |
|                   |       |      |                   |
|   CP1623 [p2]-----+   +---+--+---+-----+ CP1623 [p2] |
+-------------------+   |       |   |   +---------------+
                        |       |   |
                   +----+--+ +--+----+
                   |  SC-A | |  SC-B |
                   | SCAL. | | SCAL. |
                   +--+----+ +-+--+--+
                      |          |
                      +---+  +---+
                          |  |
                  +-------+--+-------+
                  |   S7-400H        |
                  |   CPU 410-5H     |
                  |   PN-H-CPU-1     |
                  |   PN-H-CPU-2     |
                  +-------------------+

S7-400H Connection Parameters

When WinCC connects to an S7-400H through HARDNET-IE S7 REDCONNECT, configure the S7 connection in the WinCC project with the following parameters under Tag Management > SIMATIC S7 PROTOCOL SUITE > New Connection:

Commissioning and Verification

1. Power up both S7-400H CPUs, wait for H-link up and RUN-Redundant state (LEDs: RUN green, REDF off on both).
2. Power up SCALANCE-A and SCALANCE-B. Verify the MRP ring closes within ~50 ms.
3. Power up WinCC Server A first. Install HARDNET-IE S7 REDCONNECT license and bind it to the CP1623 serial number using SIMATIC NET > Commissioning PC Station.
4. Confirm S7 connection establishes under WinCC Explorer > Tag Management; status icon must be green.
5. Power up WinCC Server B. Repeat the license binding. Verify WinCC Redundancy Synchronization is OK in WinCC Explorer under Computer Properties > Redundancy > Status.
6. From each server, force an H-system switchover in STEP 7 via H-CPU > Operating Mode > Switchover. Verify that the WinCC tag values continue to update on both servers without a single alarm freeze > 5 s.
7. Pull the network cable from one SCALANCE; verify MRP reconverges and S7 stays connected on the surviving switch path.
8. Stop the WinCC Runtime on Server A; verify Server B becomes Master within the configured redundancy timeout and clients reconnect automatically.

Common Fault Conditions

Reference Documentation

For deeper configuration of a redundancy-enabled WinCC HMI device (especially for WinCC Unified), see the official Siemens TIA Portal cloud documentation:

• Configuring redundancy — WinCC Unified (TIA Portal V21 documentation)

Refer to the SIMATIC WinCC V7.4 SP1 System Manual for the exact redundancy timeout default values, and to the SIMATIC NET PC Software Commissioning Manual for license binding procedures.