Fast background: I'm a controls engineer at a small industrial automation integrator. I've handled 100+ emergency Siemens PLC jobs in the last decade, including same-day processor swaps during unplanned shutdowns. The following FAQ is the version I give customers when they need direct answers, not a product catalog.
You'll find answers on Siemens PLC controllers, the types of PLC in the Siemens lineup, the global PLC market share for Siemens in 2024, how a 400 amp Generac transfer switch ties into a PLC system, and the real difference between a generator and an inverter. Details are current as of January 2025.
Let's clear up one naming issue first: siemens-plc is how people search, not the model name. The Siemens PLC family is called SIMATIC, and the types of PLC you will see specified today are these four groups:
If you compare PLC types by form factor, LOGO! is fixed, S7-1200 is modular, and S7-300/400 is rack-based. In practice, choose by control tier rather than by that textbook classification: micro, compact, high-end, or legacy replacement.
Here is the honest answer: choose by maintenance reality, not by CPU price. For simple standalone equipment, LOGO! is enough. For a standard single-machine application, the S7-1200 is the no-brainer because it gives you Ethernet, OPC UA, web server, and expandable I/O without overengineering. For multiple motion axes, functional safety, or very high-speed processes, the S7-1500 is usually the right call.
I also look at what the plant already knows. If the maintenance team uses TIA Portal and S7-1200s, staying in that family will save far more than the few hundred dollars difference in hardware. In March 2024, I saw a new line specified with an older S7-300 CPU only because the buyer already had one in surplus. After two weeks of integration pain, the project switched to a current controller anyway. Bottom line: buy current hardware, match the existing skill set, and pick the smallest tier that meets the safety, networking, and speed requirements.
If you searched for the global PLC market share 2024 Siemens percentage, the short answer is about 31%. The exact figure depends on the research methodology: some studies include software and services, some count only PLC hardware, and regional splits change the number. Public summaries of the 2024 ARC Advisory Group PLC market research place Siemens at roughly one-third of the global PLC market, comfortably ahead of other suppliers.
Source note: ARC Advisory Group PLC Worldwide Market Outlook, public summary accessed January 2025; the full report is paywalled, so treat 31 percent as an estimate rather than a precise accounting figure.
Market share matters for one practical reason: you can usually find spare parts, programmers, and training for Siemens PLC controllers almost anywhere in the world. But it does not mean every project should use a Siemens PLC. If you only need a small fixed controller, say so. A supplier that tells you when you don't need their biggest controller is more credible when you do.
It is not a panic-and-rip-everything-out situation, but it is no longer a wait-and-see situation either. The part that surprises most people is that Siemens does not phase out the whole family at once; it announces S7-300 phase-outs module by module. Each part number has its own life-cycle status, and the official place to check is Siemens Industry Online Support.
Last May I took a call from a plant whose S7-300 CPU had been killed by a mis-wired 24 VDC field loop. They had no spare. The CPU was already past its last order date at Siemens, so the normal distributor route closed and the search went to surplus brokers. We found a new-old-stock unit in another state, paid close to three times the old list price, and flew it overnight. The alternative was a production line down for weeks.
Do the 20-minute inventory today: write down the MLFB number from the front of each critical CPU and power supply, put one spare CPU and one power supply on the shelf, and check which TIA Portal version the spare requires. If you have a long-term plan to migrate to S7-1500, start it before a failure forces the decision.
Yes, but the correct word is supervise. A 400 amp Generac transfer switch is a UL 1008 listed assembly with its own internal transfer controller. The switch decides when to move the load between utility and generator. That logic should not live in a Siemens S7-1200 or S7-1500 unless the entire assembly has been designed, tested, and listed as a transfer switch system.
The clean integration uses dry auxiliary contacts on the ATS. Wire those contacts into 24 VDC digital inputs on the Siemens PLC. The PLC can monitor positions, alarm, and send remote test or generator start commands through relay outputs. The actual transfer stays inside the ATS, which is also what protects the generator when the PLC is rebooted or placed into STOP mode.
Here is something vendors won't tell you: most PLC-related transfer switch failures come from integration mistakes, not from PLC hardware. Someone lets the PLC influence the interlocking logic, then later puts the PLC in STOP for a download, and the ATS no longer has a clear picture. Keep the ATS self-sufficient. When in doubt, follow the exact Generac as-built wiring diagram and the UL 1008 requirements before adding any PLC points.
Short version: a generator produces AC electricity by burning fuel to turn an alternator. An inverter converts DC electricity from batteries or solar panels into AC. A generator is an energy source; an inverter is a power converter.
That distinction matters when you size emergency power. A 400 amp transfer switch is part of a generator-backed system: utility fails, generator starts, ATS transfers, and the full load returns. An inverter cannot do that by itself unless you have a very large battery bank, because an inverter does not create energy; it only changes the form of stored energy.
In a plant, you often use both: a generator for bulk backup and an inverter or UPS for sensitive electronic loads that need uninterrupted power before the generator can pick up the building load.
One more source of confusion: an inverter generator is a small portable generator with an electronic inverter stage that cleans the output waveform. It still burns fuel. If a specification says 400 amp transfer switch, that is a real generator application, not an inverter question.