I'm the procurement manager at a 45-person industrial automation company. For six years, I've overseen our Siemens PLC budget — roughly $180,000 in cumulative spending on S7-300 modules, S7-1200s, TIA Portal licenses, training courses, and service contracts.
I started this job like most buyers: I compared vendor quotes, picked the lowest number, and moved on. That approach lasted exactly one major order.
I'd found a supplier offering a batch of Siemens S7-300 modules for $340 less than the next nearest bid. I was proud of the saving for about a month — until we realised the modules arrived without the documentation our quality team required, and the supplier couldn't provide it for another week. The delay stalled a diesel generator control panel project that was already on a customer's critical path. The penalties wiped out the $340 and then some.
That's when I adopted the framework I still use today. Before buying anything, I ask: what is the difference in total lifetime cost between these options — including rework, downtime, and hidden fees? Here are the three comparisons I run most often.
Search for 'siemens plc training courses uk' and you'll see what I saw back in 2023 — a three-day SITRAIN course covering S7-300 basics in TIA Portal, quoted at £1,450 excluding travel. That's not a small number for a mid-sized company.
The alternative was tempting: Siemens publishes detailed manuals online, and plenty of free tutorials walk through S7-300 basics, memory areas, timers, and programming patterns. I honestly believed a competent technician could learn everything on the job without spending a pound.
The upside of sending one of our techs to the course was obvious: faster, more reliable programming on client projects. The risk was just as obvious — £1,450 spent on a course that might be too basic, and a technician away from billable work for three days. I kept asking myself whether the training was worth potentially wasting a quarter of our annual training budget.
I sent him anyway. Two weeks after that Manchester course, he rebuilt the control logic for a client's fire pit control panel — a compact Siemens LoGo! application with gas valve sequencing, an ignition interlock, and alarm handling. Before the course, that task would have taken him a full week of trial and error. He did it in two and a half days.
Not because he learned advanced secrets, but because he stopped making the basic mistakes: duplicate coils, incorrect addressing, sloppy timer handling. He was thinking in scan cycles instead of hoping the code would work.
Now, let me be fair to the free route. I've worked with excellent self-taught engineers. But when I pulled the timesheets for our three technicians over 18 months, the formally trained engineer logged about 30% fewer debugging hours per project than the self-taught ones. In total cost terms, that difference was way bigger than the course fee.
The verdict: if your company works with Siemens PLCs regularly, paid training is a no-brainer. If you're an individual learning S7-300 basics on your own, start free — but track your time. If you're spending weeks solving problems a course would have covered in one afternoon, free isn't free.
My second comparison is about how we handle diesel generator service.
Many of our customers run generators for backup power — hospitals, server rooms, manufacturing lines — and most gen-sets rely on a Siemens S7-300 PLC for start sequencing, load switching, and fault logging. These systems need attention whether or not there's an outage happening.
A preventive diesel generator service contract — quarterly inspections, load bank testing, and a diagnostic read-out of the PLC fault buffer — costs about £1,800 to £2,500 per year per site. Split across four visits, it's a few hundred pounds a time. It's also an easy line item to cut in a budget review. I did it once, and I still regret it.
Eight months after we cancelled a client's service contract, their generator failed during a routine start test. Root cause: a S7-300 power supply module that had been writing low-level faults to the diagnostic buffer for months. Nobody read it, because nobody was looking.
What did that emergency response cost?
That's over £900 of visible costs, versus the £2,100 preventive service contract we had cut. And the bitter part: the routine inspection would have caught the failing module, replaced it for £400 in normal time, and nobody would have noticed anything.
The worst part wasn't the money. It was telling the customer we had caused this by cancelling their preventive service.
The verdict: if you can truly tolerate unplanned outages, cancel the service contract and bank the money. But first calculate what an hour of unplanned downtime actually costs you, and multiply it by the probability of a failure. The math is why preventive maintenance is an insurance policy, not an expense.
My third comparison involves a fire pit control panel and a circuit breaker. This is the one I'll never live down.
A customer wanted a fire pit control panel built as cheaply as possible. Their facility guy had learned how to install a circuit breaker from a YouTube tutorial, and he was confident he could handle the electrical side. He installed a breaker with the wrong trip curve, the panel failed our factory acceptance test, and the rework cost $1,800. The licensed electrician who fixed it properly charged $250.
That story is a perfect metaphor for what I see when companies go bargain-hunting on Siemens PLC components.
A genuine S7-300 CPU (say, a CPU 315-2 PN/DP) costs about $1,100-$1,300 new from an authorised distributor. A used unit from a reputable reseller runs $500-$700. A compatible import can be had for $150-$250. Every dimension of that comparison looks tempting — until you zoom out.
Now, I'm not an electrical engineer, so I'm not going to lecture you on trip curves or protection coordination. What I can tell you from a procurement perspective is this: the part's price is the smallest number in the calculation if the part fails at the wrong moment.
Put a $200 compatible module in a fire pit control panel where its job is to close a gas valve when the ignition fails. Or put it in a diesel generator controller responsible for starting a hospital's backup power at 3am. If that module fails, you're not replacing a $200 part — you're dealing with a fire hazard, a production outage, and an insurance conversation.
Does that mean you must always buy new genuine modules? Not necessarily. For non-critical bench work and laboratory demonstrators, we've bought used genuine S7-300 CPUs (this was circa 2024) and saved around 40%. We tested every module before installation and documented the results. That's the responsible middle ground.
The verdict: buy genuine when safety or production continuity is on the line. Use tested genuine modules for non-critical work. Treat compatible imports as consumables. And if someone on your team learned how to install a circuit breaker from YouTube, don't let them near a control panel until a licensed electrician has signed off.
I've tracked every relevant invoice for six years — $180,000 in cumulative spending. The pattern is unmistakable: the projects where we invested in training, preventive service, and quality components have the lowest total cost per successful project. The projects where we chased the lowest quote show up later as emergency purchases, rushed replacements, and rework hours.
Five minutes of verification beats five days of correction. That's not a motivational poster — it's the summary of six years of procurement line items. I keep a 12-point checklist I review before any PLC-related purchase, and it has saved us money more times than I can count.
If you're on the fence about any of these decisions, here's my practical guidance:
There's something satisfying about finishing a project without a single emergency purchase line item. It doesn't happen by accident. It happens because somebody took the time to compare total cost instead of quote price.