Use this checklist if you're about to order a Siemens PLC for a project—whether it's a small machine, a water treatment upgrade, or an emergency backup power skid. I'm an office administrator for a 40-person automation integrator. I manage about $200k in PLC hardware orders every year, and I report to both operations and finance. This is the checklist I wish someone had handed me in 2020.
Here are 8 checks I run on every Siemens PLC order. Some are obvious. One is almost never on anyone's template. All of them have cost me time or money at some point.
Siemens PLC model numbers look simple until they don't. An S7-1200 CPU 1214C has multiple part numbers, and the firmware revision tells you what TIA Portal versions can actually address it. If you order by description only, you can end up with a CPU that needs a firmware update before it can be programmed.
Check the Siemens part number yourself. Don't let the distributor's salesperson guess. I once approved a PO for an 'S7-1200 CPU' without catching the firmware difference. It cost us a day of labor on site.
TIA Portal versions are not backward compatible with every CPU firmware. A CPU that requires TIA V18 won't open in V15. That's a common problem when the warehouse sends 'the same thing you ordered last year.'
Ask the engineer: what TIA version is the project running? Then look it up on Siemens Industry Online Support. Trust but verify. Real talk: the distributor's 'it should work' has burned me before.
If you've been searching for 'siemens s7-300 plc price', here's the honest answer: S7-300 is an old platform. Some CPUs are still sold, but a lot of the family is in phase-out. New old stock can be expensive. Used modules are cheaper but riskier.
From distributor quotes I've seen in 2024 and early 2025, used S7-300 CPUs often run $300 to $700. New old stock can be $800 to $2,500 depending on the CPU and availability. For a new project, I'd spend that money on an S7-1200 or S7-1500 instead. You get better support, faster delivery, and a longer spare-part outlook.
I should add: PLC pricing changes with tariffs and inventory. Get a written quote with a validity date.
Market share sounds like a finance topic, but it matters when you're waiting for a spare module. In the 2024 global PLC market share reports, Siemens and Rockwell are consistently the two names at the top. Siemens leads overall worldwide; Rockwell is stronger in North America.
For a buyer, the practical point is this: Siemens has a huge installed base, so you'll usually find training, parts, and engineers who know the platform. If your local support ecosystem is Rockwell-heavy, that's a real consideration. Don't buy on brand pride. Buy around who will help you at 2 a.m. And if cybersecurity compliance is in your spec, check whether the specific CPU carries IEC 62443 certification on the Siemens support site.
Here's something vendors won't tell you: standard PLC quotes often assume you already have the power supply and memory card. The first time I ordered an S7-1200, I forgot the 24V DC power supply. We had a CPU, a relay, and no way to power anything.
Check the quote for the power supply, memory card, PROFINET connector, and bus connector. If the CPU doesn't have integrated PROFINET, add the network module. This is the step I tell every new administrator to check twice.
A Siemens PLC doesn't care whether it's controlling a production line or a generator. But the equipment around it matters. For a home or small facility, you need a whole home transfer switch. That's what stops a generator from backfeeding the utility and keeps the loads safely connected to one source.
For industrial projects, an automatic transfer switch (ATS) does the same job with a heavier enclosure. The PLC and ATS are separate products, but they need to talk to each other. Put the ATS in the project scope before you order. Don't assume your PLC vendor will supply it.
During one commissioning, permanent power wasn't connected. The controls crew needed to test the PLC and the field wiring anyway. We searched for 'diesel generator rental near me' and found a small portable unit for two days.
It was enough to power the PLC, the 24V supply, and a few I/O circuits. A rental is the right call if you only need temporary power for commissioning. Just check the voltage and phase match your equipment. A 120/240V generator won't run 480V three-phase gear.
People use 'electrical panel' and 'breaker box' like they're the same thing. On a PLC project, they are not. A breaker box is usually the residential load center where the utility feed splits into branch circuits. An electrical panel is a broader term; when I'm buying controls, the panel is the enclosure that holds the PLC, relays, terminals, and a disconnect.
Ask your vendor: does this quote include the panel, or just the PLC components? If you don't clarify it in writing, someone will add the enclosure and wiring as a change order. I've seen that happen more than once.
One more thing: ask for a sample invoice before the first order. If a vendor can't provide a proper commercial invoice, finance will have a bad day.
Here's the thing: I've made most of these mistakes at least once.
Small orders deserve real service. A vendor that answers a small S7-1200 order with clear delivery dates and a correct invoice is worth more than one that only smiles on a $20,000 quote. When I was starting out, the vendors who treated my $200 orders seriously are the ones I still use for $20,000 orders. Small doesn't mean unimportant—it means potential.
If you keep the PLC, power supply, backup power, enclosure, and delivery terms straight, your install will go smoother than you expect. Not perfect. But better than the time I showed up with a CPU and no power supply.