I’ve Bought Industrial PLCs for 6 Years. The PLC Isn’t the Starting Point

Most industrial automation purchases start at the wrong end. Companies pick the PLC first — the brain — and then try to bolt a SCADA system, network infrastructure, drives, and components around it. I think that’s completely backwards.

After six years of buying industrial PLCs, variable frequency drives, and everything connected to them, here’s my conclusion: the PLC is not the starting point. The system is.

Don’t get me wrong — PLC quality matters. A reliable industrial PLC is the foundation of any automated line. But the difference between a good purchase and a bad one is almost never the CPU speed. It’s how that PLC fits into the larger system: how it connects to the SCADA layer above it, how it talks to the drives below it, and whether you’ve thought about your PLC network before you pick a model.

If you’ve ever signed off on a PLC purchase without asking how it will communicate with your SCADA system, you already know where this is going. The PLC itself is rarely the problem. It’s everything around it that eats your budget and your timeline.

The PLC and SCADA Integration Trap

When I took over purchasing in 2020, the most common request I heard was, “we need a PLC for this production line.” Sounds simple. It isn’t.

Here’s something vendors won’t tell you: a PLC’s compatibility with a SCADA system is often determined by drivers, middleware, and OPC servers that cost extra and take weeks to commission. People assume the PLC is the product. The reality is the integration is the product.

We bought a controller once that looked outstanding on paper — fast scan times, plenty of I/O, attractive price. Got it installed. Then the SCADA integration required a third-party communication server that our integrator spent a full week configuring. What should’ve been a weekend retrofit turned into a two-week project. The hardware savings evaporated the moment we paid for integration hours.

I’m not naming the brand, because that’s not the point. The point is how we bought it: we treated the PLC as the decision, when we should’ve treated “PLC and SCADA connectivity” as the decision.

The bottom line: when someone says “we need a PLC,” the next question should always be, “what SCADA system is it connecting to, and what driver does that require?” If the answer is unclear, you’re not ready to buy.

PLC Network Architecture Determines the Project — Not the CPU Speed

This is where most procurement people check out, and I don’t blame them. Networks aren’t exciting. But here’s what I’ve learned the hard way: the PLC network architecture determines your total cost more than the PLC brand does.

Think about it this way. A PLC’s CPU speed determines how fast it executes logic. But if the network it’s on can’t move data reliably, that speed means nothing. You’re buying a sports car and parking it on a dirt road.

In our 2024 vendor consolidation project, we replaced controllers across three facilities. Processing 60-80 orders annually gives me a clear picture of what things cost, but I still almost got this wrong. We were comparing CPU specs, memory, redundant power supplies — the usual checklist items. What actually determined the outcome was network coverage and protocol support.

We standardized on Mitsubishi PLCs partly because their CC-Link and Ethernet options integrate cleanly with our infrastructure. But honestly, the more important decision was mapping the network first: every remote I/O rack, every drive, every HMI that needed to communicate. That roadmap dictated the PLC model. Not the other way around.

And another thing about PLC networks: don’t underestimate cabling and commissioning. The hardware cost of adding network nodes can double once you factor in shielded cable, termination resistors, and the integrator’s time to get everything talking. These costs are rarely in the initial quote. Referencing IEC 61131-3 helps standardize the programming side, but networking standards aren’t nearly as universal — so the network plan deserves far more attention than it usually gets.

Here’s what you need to know: the part number is secondary to the network plan. Always.

The VFD and Component Blind Spot That Costs Real Money

Now for the counterintuitive part. The smaller and less glamorous components can sink your budget faster than the main equipment ever will. This is the stuff nobody in the procurement conversation talks about.

Take variable frequency drives. A three-phase frequency converter isn’t just a “big switch.” It’s a complex piece of power electronics. When you’re modernizing a control system, you have to think about how these drives communicate with the PLC. Modbus? DC bus sharing? Pulse train references? These questions determine everything from wiring costs to spare parts strategy. If the drive and the PLC can’t speak the same protocol, you’ll spend a fortune on converters or a second integrator visit.

And then there’s the really granular level — semiconductors.

When a drive fails after a surge, the repair usually comes down to swapping out an IGBT module. A part like the FGA30N120 — that’s a 30A, 1200V IGBT, for anyone curious — ends up being the difference between a one-day repair and a four-day shutdown. I learned this the expensive way.

A few years back, a $20,000 production line sat idle for four days because nobody had stocked a spare IGBT for the frequency converter. The distributor’s lead time was five days. We paid $300 in expedited shipping fees on a component that costs less than a single hour of downtime, just to get the line moving again. Meanwhile, our other plant had been through the exact same scenario a year earlier and now keeps a locked drawer of spare IGBTs. The maintenance manager there buys FGA30N120 modules in pairs without even asking for approval.

Want to know the irony? We were in the middle of a “cost optimization initiative” and had trimmed spare parts budgets to fund PLC upgrades. Penny-wise, pound-foolish. The $300 rush fee was nothing compared to the lost production hours — that was closer to $12,000 in downtime.

Also, let’s clear up a common misunderstanding: a variable frequency drive is not a phase converter. I’ve seen quotes where someone tries to run a three-phase motor from a single-phase supply using a standard VFD. It won’t work. A VFD needs a clean three-phase input to do its job. If the facility only has single-phase power, you need either a genuine phase converter or a drive specifically designed for single-phase input.

Why does this matter to a buyer? Because the person writing the PO doesn’t always know the difference, and vendors don’t always ask the right questions. The cost of a wrong specification isn’t just the price of the drive — it’s the days of downtime while you figure out why nothing works. That’s a deal-breaker at any budget level.

“But My Integrator Handles All That” — Rebuttals I Hear on Repeat

I’ve had this conversation at least a dozen times. And I’m not saying integrators aren’t worth their fees. A good one is worth every dollar. But here’s the thing: if you can’t specify the basics — what network you’re on, what SCADA you’re integrating with, whether your facility’s power matches the drive input — you’re leaving every decision to someone else’s schedule, billable hours, and brand preferences.

That’s not delegation. That’s abdication. I learned this the hard way with a parts vendor that couldn’t provide proper invoicing for a rush shipment — handwritten receipt only. Finance rejected the expense, and I ended up eating $2,400 out of the department budget. Now I verify a supplier’s invoicing process before I commit to anything.

And to the folks who say “all PLCs are basically the same now” — no. They’re about as similar as trucks with engines and wheels. Connectivity, programming software, spare parts availability, and local technical support vary widely between brands. Once you standardize on one platform, switching later is painfully expensive. Brand standardization is a long-term marriage, not a casual date.

Bottom Line: Buy Outcomes, Not Hardware

So here’s where I land after six years and well over $1.5 million in automation purchases: stop buying hardware. Start buying outcomes.

There’s something satisfying about getting this right. After all the stress of commissioning, seeing a line run smoothly — PLCs, SCADA, drives, and networks all working as one system — that’s the payoff. No midnight calls. No angry production managers. No rush orders. Just a quiet line humming along.

An informed buyer asks better questions. Here are mine:

• What SCADA system is this PLC connecting to, and which driver does the integration require?
• What network protocol will carry data between the PLC, the drives, and the HMIs?
• Does the equipment match the facility’s power supply? Three-phase input drives need three-phase power.
• What spare components keep the system running when a device fails? (Hint: FGA30N120 is a good place to start.)

Ask those questions before you sign anything. Map the system before you spec the parts. And, for the love of your budget, stock the spare IGBT.