I Buy Siemens PLCs for a Living — Here's My 7-Step Cost Checklist Before Any PO

This checklist is for anyone who has to sign off on a Siemens PLC purchase — procurement managers, automation engineers with budget authority, or systems integrators quoting a project. It won't help you if you're buying one Logo! for a hobby bench. It's built for people spending real money on siemens-plc hardware and trying not to get burned by the line items that don't show up on the first quote.

Seven steps. I run them in this order every time, and I've been doing it for seven years across roughly $420,000 in cumulative automation hardware spend.

Step 1: Lock the exact model and I/O count — not the family

"S7-1200" is not a part number. The plc siemens s7-1200 1214c entradas y salidas configuration alone has several variants: 14 digital inputs with 10 relay outputs (AC/DC/RLY), or 14 DI with 10 transistor outputs (DC/DC/DC), plus 2 analog inputs on both. The relay version is cheaper upfront. The transistor version is what you want if you're driving anything at high switching frequency.

I've watched a project manager order the relay variant to save $60 per unit, then buy external interposing relays at $18 each for 12 outputs. That's $216 to save $60. Do the math before the PO, not after.

What to check:

• Exact order number (6ES7...), not just "1214C"
• Output type: relay vs. transistor
• Whether the 2 onboard analog inputs are enough, or you need a signal module
• Firmware version compatibility with your TIA Portal install

Step 2: Size the CPU for the machine you'll have in three years

The siemens plc 1500 line is where budgets quietly blow up. A 1511-1 PN is fine for a small cell. But if the customer mentions "we might add a second line next year," you're now sizing for growth, and the next CPU up is often 40% more expensive with a different memory card requirement.

My rule: spec the CPU at 60% of projected memory and connection count. Not 90%. I learned this the hard way in 2022 when a customer added four remote I/O drops to a system we'd sized at 85% capacity. The CPU swap cost us $2,300 in parts and two days of re-validation — on a project where we'd already quoted fixed price.

"The CPU is the one component where over-speccing is almost always cheaper than under-speccing."

Ask yourself: how many PROFINET devices today? How many in 24 months? If the answer is "I don't know," buy one tier up.

Step 3: Price the TIA Portal license correctly — this is where quotes lie

TIA Portal licensing is the single most common source of post-PO surprises I've seen. Step 7 Basic comes bundled with some S7-1200 kits. Step 7 Professional does not. WinCC Unified is a separate line. And the floating vs. single license distinction matters the moment you have two engineers programming.

What most quotes don't include:

• The correct TIA Portal version license (V17 vs. V18 vs. V19 — they're not interchangeable)
• WinCC Runtime licenses per HMI panel
• Simulation software (PLCSIM) if you're doing FAT before shipping
• Teamcenter or version control add-ons, if your shop uses them

I now require every PLC quote to itemize software licenses separately. One distributor quoted me a "complete package" in 2023 that turned out to be hardware plus a Basic license — we needed Professional. The $1,850 delta showed up three weeks later as a change order.

Step 4: Add training and support cost to the TCO spreadsheet

This is the step most procurement teams skip, and it's the one I regret ignoring early in my career. A new S7-1500 platform means your maintenance techs need TIA Portal training. Siemens instructor-led courses typically run $2,000–$3,500 per seat, depending on level and location. Multiply by however many people touch the line.

Then add the support contract. Siemens technical support is not free after the warranty window. A support agreement on a mid-size installation typically runs a few hundred dollars per year — trivial on its own, but I've seen it dropped from budgets, then re-added at a premium when a line goes down at 2 AM.

Total cost of ownership (i.e., not just the unit price but every dollar attached to keeping the thing running) is the number that matters. If your spreadsheet only has hardware and software columns, it's wrong.

Step 5: Confirm cybersecurity compliance before the auditor does

IEC 62443 compliance isn't optional anymore for most of our customers — especially anyone supplying into food, pharma, or water treatment. Ask your distributor for the security documentation package up front. If they hesitate, that's information.

This was accurate as of Q1 2025, but standards and customer audit checklists drift. Verify your specific end-customer's requirements before assuming IEC 62443-3-3 is enough. I had a customer last year who required 62443-4-2 component certification documentation on the CPU, and we didn't have it in the quote package. Took two weeks to source.

Step 6: Don't forget power infrastructure — and don't confuse industrial backup with consumer gear

PLC cabinets need clean, backed-up power. For most industrial installations, that means a proper UPS, not a portable generator. I've been asked whether a dual fuel remote start inverter generator could back up a PLC rack, or whether a what is the best solar generator to buy search would solve an outage problem. Both questions miss the point: consumer power products are not rated for industrial duty cycles, transfer times, or harmonic tolerance. If you need backup for a PLC, size a UPS to ride through the transfer, and put the generator behind it for extended outages.

Budget line: UPS is usually 5–10% of the control panel cost. Easy to forget, expensive to retrofit.

Step 7: Build the spare parts allowance into the first PO

Industry practice is to hold 10–15% of installed base value in critical spares. On a project with eight S7-1200 CPUs, that's one spare CPU, one spare signal module, and one spare power supply. Order them with the initial PO — they're cheaper bundled, and you avoid the 4–6 week lead time when a unit fails.

I keep a simple rule: if the line can't run without it for 48 hours, it goes on the spares list. That's usually the CPU, the power supply, and any specialty communication module.

Common mistakes I've made (so you don't have to)

Substituting consumer components. I once had a contractor suggest using a maytag oven control panel as a stopgap HMI display because it was "basically the same screen." It is not. Industrial HMIs are rated for temperature range, vibration, EMI, and 24/7 duty. Consumer panels are not. That conversation ended quickly, but it happened.

Trusting verbal lead times. Get delivery dates in writing with penalty clauses on critical-path items. Looking back, I should have pushed for that on every project over $50K. At the time, it felt like overkill for "trusted" distributors. It isn't.

Forgetting the firmware/TIA Portal version lock. If your shop is on V17 and the distributor ships V19 hardware, you may be fine — or you may be reflashing firmware before commissioning. Confirm compatibility in writing.

This approach worked well for us, but we're a mid-size systems integrator with predictable project pipelines. If you're a plant maintenance team buying one CPU at a time through a distributor portal, some of these steps collapse. And if you're dealing with international sourcing or export-controlled configurations, there are layers I haven't had to navigate. Your mileage may vary.

The checklist, in order: exact part number, CPU headroom, software licenses itemized, training and support in TCO, compliance documentation, power infrastructure, spares allowance. Seven steps, one spreadsheet, and far fewer change orders.