How to Source Delta PLCs, VFDs, and Relays: A 7-Step Buying Checklist

When This Checklist Applies

If you're the person placing procurement orders for industrial automation parts—Delta PLCs, VFDs, relays—and you need to get a clean purchase order out to the floor, this checklist is for you. Seven steps. No fluff. If you're short on time, skip to Step 4—that's the one most buyers gloss over.

Quick context: I handle purchasing for our company—roughly 60 to 80 orders a year across a dozen vendors. Engineering tells me what's needed, I make it happen. I've made some mistakes worth sharing so you don't have to repeat them.

Step 1: Get the Spec in Writing Before You Call Anyone

My biggest screw-up came from accepting a verbal request. An engineer said "get a Delta PLC," so I ordered a DVP series unit. Turns out they needed a safety PLC. Completely different animal.

So: before you dial a single vendor, get the spec in writing. Ask your engineering contact for:

• The exact model or series (e.g., Delta DVP-SS2, DVP-ES3—not just "Delta PLC")
• I/O count and type (digital vs. analog, how many inputs/outputs)
• Communication protocol (Modbus RTU, Ethernet/IP, etc.)
• Power supply and mounting requirements
• Any safety functions—and if so, whether it's a safety-rated PLC or just a standard one doing safety-adjacent work

"We want a Delta PLC" is only half a sentence. Filling in the rest takes five minutes and saves you a return shipment later.

Step 2: Pull the Right Catalog PDFs

Next: the Delta PLC catalog PDF and the VFD catalog. Both are available on the manufacturer's site. Using the wrong revision means everything downstream is wrong too.

I made this mistake once. Used a Delta PLC catalog PDF from two years prior—the drive specs listed firmware that had since been updated. The units arrived with different default parameters, and our programmer spent half a day reworking the logic.

So: before you download, check the publication date. Delta updates these documents regularly. If engineering has asked for a specific revision, have the vendor confirm in writing which one they're quoting from. And if you're specifying for VFD OEM applications, ask for the OEM-specific selection guide—the default parameter sets can differ from the general catalog.

Step 3: Vet the Supplier Before You Ask for a Quote

Before I get pricing from anyone new, I run a basic check. Ten minutes, and it's saved me from several bad situations.

Here's what I verify:

• Can they issue a proper invoice? This is non-negotiable. I once had a vendor offer a handwritten receipt "to save on paperwork." Finance rejected the expense report outright. That vendor is no longer in our system.
• Are they an authorized distributor? Ask directly: "Are you an authorized Delta distributor?" If the answer is vague, that tells you something.
• Can they provide lot traceability or warranty info? Legitimate channels can. Gray-market sellers usually can't.

If this step raises flags, walk away—regardless of how good the price looks.

One more thing about the "local is always faster" assumption. That thinking comes from an era before modern logistics. Today, a well-organized remote supplier can often beat a disorganized local one. Don't default-score a vendor just because they're not on the same street.

I have mixed feelings about consolidating to one supplier. On one hand, fewer vendors means less overhead and often better pricing. On the other, redundancy saved us during the supply chain mess in 2023. I compromise with a primary-plus-backup model.

Step 4: Calculate Landed Cost, Not Unit Price

This is the step most buyers skip. My view: the lowest quote is rarely the cheapest option. What I mean is—the sticker price is just one slice of the pie.

Here's what actually goes into total cost:

• Freight and customs/clearance fees
• Companion parts—relays, terminal blocks, wiring, mounting hardware
• Engineering time for configuration and commissioning (including rework if the wrong part ships)
• Time spent managing returns or claims if something fails
• Downtime cost if the production line is waiting on a delayed delivery

I once switched to a vendor who was $200 cheaper on relays. The contact ratings weren't right for our inductive load. Commissioning got delayed two days. Between the engineer's overtime and the re-order, we were out roughly $1,500 (if I remember correctly, it came to about $1,420—I try not to look at that invoice again). Yes, it stung.

Now, whenever I see a price that's way lower than everyone else's, my first thought isn't "deal"—it's "what's missing?" Either the quality is off, the service is stripped down, or there's a hidden cost waiting later.

Step 5: Relay Sourcing—Where Most Wholesale Buyers Slip Up

Relays look simple. They're not. This is where wholesale buyers get tripped up most often because the focus lands entirely on price.

If you're figuring out how to choose a relay for wholesale, here's what needs to be confirmed:

• Coil voltage—24VDC? 110VAC? 220VAC? Get this wrong and it won't work at all.
• Contact rating—current and voltage. Account for whether the load is resistive or inductive. (The $1,500 lesson above came from this exact oversight.)
• Contact form—SPDT, DPDT, or something else?
• Mechanical and electrical life ratings—different brands rate these differently. Don't just compare the headline number.
• Certifications—UL, CE, IEC. The specific model may vary by deployment location.

Here's something vendors won't tell you: the spec sheet they quote from is often for the lowest-tier variant in a series. Upgrade to a higher contact rating and the price shifts. So after you get a quote, match the model number character-for-character against the datasheet.

Also—don't cross-compare relay brands on headline numbers alone. A 10A contact rating on one brand under inductive load may behave very differently from a "10A" on another. Check the load curve in the datasheet.

Step 6: Confirm Compliance and Documentation

Last technical gate before you order. Industrial automation components carry compliance requirements, particularly for export or industry-specific installations.

Confirm:

• The product carries certifications required for your market (CE, UL, RoHS, etc.)
• The vendor can supply the paperwork your finance and receiving teams need—packing list, commercial invoice, certificate of origin if applicable
• For safety-rated PLCs, the relevant functional safety certification

This might look like paperwork. But it determines whether your order clears receiving and passes audit. I've had an expense rejected over a missing certificate. Starting the process over is not fun (unfortunately, it happens more often than it should).

Step 7: Lock In Lead Time, Price Validity, and Payment Terms

By now you've picked the supplier and confirmed the specs. Convert the verbal agreements into written confirmation.

Ask the vendor to reply by email confirming:

• Exact lead time (a date, not "a few weeks")
• How long the quoted price holds (this matters when raw material costs are fluctuating)
• Payment terms (Net 30, deposit percentage, etc.)
• Any penalties for late delivery

I know it feels like extra steps. But I once had only a few hours to decide before a shipment window closed. Normally I'd get everything in writing first, but there was no time. Went with a verbal quote from a trusted vendor. At order time, they said "oh, that price was only for the previous batch—it went up." Lesson learned. Now everything goes through email, even if it takes an extra day.

Watch-Outs and Common Mistakes

Seven steps done. Here are the closing reminders:

• Don't change specs mid-order. Once the PO is out, resist the urge. Changes ripple through lead time and cost.
• Track catalog versions. The Delta PLC catalog PDF and VFD catalog get updated. Note the revision when you download.
• Don't skip relay fine print. Coil voltage and contact rating are the two most common failure points. I've seen experienced buyers trip on these.
• Be wary of quotes significantly below market. If the price is unusually low, there's usually a reason—wrong part, stripped service, or hidden fees later.
• Keep all email correspondence. Not about trust. It's about protecting yourself.

One last thought. When procurement runs smoothly, it feels like nothing happened at all. That's actually the goal.