When I first started handling PLC purchases for our plant, I figured the smart move was simple: find the lowest quote on the CPU, submit the PO, and move on. Three budget overruns later—one of them big enough to get flagged by finance—I stopped treating Siemens PLC procurement like a commodity parts order. If you’re about to order hardware, this is the checklist I wish someone had handed me before my first S7-1200 purchase. It’s seven steps. The first six take about an hour at your desk. Step seven is the one most people skip.
Who’s this for? Engineers who got told to handle the PLC order, small and mid-size panel builders, and maintenance managers who know the machine they need but not the purchasing process. If that’s you, work through the steps in order—and don’t jump to the vendor quote until you’ve done Step 2.
Siemens is a massive company, and the PLC side alone spans three families you’re likely weighing:
That sounds basic, but I have personally reviewed a PO that ordered an S7-1500 for a job that only needed an S7-1200, and another where the reverse happened because “the bigger one is safer.” The hardware price is the first number people compare, and in my experience it’s the least important number in this exercise.
Rule of thumb I use now: assume software, accessories, and commissioning can add 30–50% to the hardware price. It’s not exact, but it’s a realistic gut check.
Here’s the mistake that taught me about total cost. In my first project, I allocated about $4,800 for hardware and zero for software. The TIA Portal license came out to roughly $2,000 (I might be misremembering the exact figure, but it was a four-digit number I hadn’t planned for). That’s a 40% add-on that nobody warned me about.
Confirm three things with your vendor before you commit:
The software line also needs engineering hours. TIA Portal is powerful, but it has a learning curve. If a contractor is doing the programming, ask for programming hours as a separate quote item. If you’re programming in-house, add a 20% contingency to the time estimate. I have yet to see a TIA Portal project come in under the original hour estimate. I want to say it has happened once, but don’t quote me on that.
Siemens CPUs often ship without the SIMATIC memory card. It’s a small line item—somewhere in the $50–$90 range—but if nobody orders it, the CPU won’t start in certain operating modes. The same goes for the 24 V power supply, PROFINET cable, mounting rail, and terminal blocks. I’ve seen a “complete” quote that was short about $400 of accessories because the sales engineer assumed the panel builder would supply them.
A vendor once offered us a “free setup” that ended up costing $450 more than the next quote once accessories and assembly were added. Read the quote line by line, and ask for a full BOM, not a price.
If your application uses variable-frequency drives, don’t leave drive commissioning as an unnamed “controls guy” task. Siemens SINAMICS drives have their own parameter sets, and the fault codes they throw are often misread during startup. F0001 (overcurrent) and F0002 (overvoltage) are classic examples: they look like hardware failures, but in a new installation they’re just as likely to be a wrong ramp time or an incorrect motor data parameter.
Drive troubleshooting will probably take longer than anyone estimates. At least, that’s been my experience across roughly a dozen integration projects. A rough rule from our cost tracking: budget one commissioning day for the first drive, then half a day for each additional drive—and don’t be upset if you need a bit more.
The most overlooked budget category is the one-hour checkout that saves the three-week emergency. For motor starter circuits, a standard test is to check the starter solenoid with a multimeter: measure the coil resistance against the datasheet value, then check voltage drop across the contacts while the coil is energized. It’s so basic that it feels like it doesn’t belong on a professional checklist. It does.
And then there’s the time I skipped it. I was on-site during a commissioning because the budget was spiraling and I wanted to see where the hours were going. There was a row of starter solenoids, and I tested all but one—because “coils either work or they don’t.” That one failed in week two. The PLC logic was fine. The whole problem was a $40 part. That was the one time it mattered.
I built a TCO spreadsheet after getting burned on hidden fees twice. Comparing hardware price across three vendors takes thirty minutes. Comparing support response time, local stock, and what the vendor actually does when something goes wrong takes longer—but that’s where the real difference lives.
The spreadsheet itself is simple: one column per vendor, rows for unit price, shipping, software, accessories, support (what does one support call actually cost?), and delivery lead time. The line that surprises people is the last one—how many days is your line down if this vendor can’t deliver a spare part? Multiply that by your hourly cost of downtime.
Everything I’d read about procurement said to chase the lowest quote. My experience tracking about $180,000 in cumulative spending across six years suggests otherwise. The vendor I have a long-term relationship with has saved me more money in emergency support than I’ve lost on their slightly higher unit prices. To be fair, the low-quote vendors do force the bigger ones to keep their pricing honest—so we still ask all three for numbers.
Standard S7-1200 and S7-1500 units are built for controlled indoor environments. Siemens publishes ambient temperature ratings in the datasheet, and for many standard CPUs that’s around 0–60 °C depending on mounting orientation. That’s fine inside a panel in a factory. It is not automatically fine for outdoor installation, hot climates, or coastal sites where salt air finds its way into every enclosure.
I remember a project that shipped a well-built marine panel for a vessel operating in the Red Sea. It had a slide-out control panel so technicians could pull the whole assembly out at the dock for maintenance. In the workshop it looked perfect. In service, the standard CPU kept overheating because the enclosure trapped all the heat and the ambient temperature sat right at the edge of spec. The lasting fix was the SIPLUS version, which has a wider temperature range—and the cost of swapping it in after commissioning was several times the price difference.
Before you place the order, put the installation condition in writing: indoor, outdoor, or coastal. If the answer is anything other than “indoor,” expect your vendor to quote a SIPLUS CPU or a better enclosure strategy.
This checklist works for most S7-1200 / S7-1500 / LOGO! purchases. At least, that’s been my experience with small and mid-sized projects. If you’re buying hundreds of units across multiple plants, your process will look different—that’s volume-agreement territory. But an hour spent on these seven steps will probably save you from the most common budget surprises.