Siemens Motors FAQ: 8 Questions to Ask Before You Order

Every time someone in our plant says "we need a motor," the same questions come up. I've been ordering Siemens motors and drives for five years—roughly 40 orders, maybe $300K total—and this is the FAQ I wish I'd had in 2020 when I took over purchasing.

Questions We'll Cover

• What's the difference between Siemens motor families?
• Which servo motor do I need—and where's the 1FK7 catalogue PDF?
• Servo vs. stepper: which one actually fits?
• Stepper motor wiring: why does it trip everyone up?
• Permanent magnet or induction: how do I decide?
• Is Siemens worth the premium?
• How do I decode a Siemens motor part number?
• What do these motors actually cost?

1. What's the difference between Siemens motor families?

Sounds basic, but it's where wrong orders start. Four families you'll actually see on a PO:

Induction (asynchronous) motors—the workhorses. Pumps, fans, conveyors. Robust, cheap to repair, fine on direct-online (DOL) start or with a VFD.

Servo motors—high-precision, closed-loop with encoder feedback. Packaging machines, CNC axes, robotics. If someone asks for "a Siemens servo," it's usually the 1FK7 series.

Stepper motors—open-loop, discrete steps, modest speed. Simple positioning, low cost.

Permanent magnet (PM) motors—higher efficiency and torque density than induction, but they need a VFD and careful engineering.

Most buyers focus on kW and frame size. What actually causes returns? Efficiency class, duty cycle (S1–S10), encoder type, brake voltage. That's where the disconnect happens.

2. Which servo motor do I need—and where's the 1FK7 catalogue PDF?

The 1FK7 catalogue PDF is on Siemens Industry Online Support—search "SIMOTICS S-1FK7," filter by PDF, and download the current edition. It's the definitive source for configurations, torque curves, and ordering data.

Here's my rookie mistake: in my first year, I picked a 1FK7 from the catalogue but didn't specify the encoder option correctly. It arrived. It didn't match the machine's existing cabling. $1,180 and a two-week delay, gone. A lesson learned the hard way—plus a conversation with finance I'd rather not repeat.

Why does this matter? Because the catalogue isn't a brochure—it's the part-number source. Every letter and digit in the order code means something. If you're not 100% sure, send the complete part number to the distributor before you buy. I send sales a screenshot every time. Annoying? Yes. Worth it? Absolutely.

3. Servo vs. stepper: which one actually fits?

The "what stepper motor should we use" conversation comes up more than you'd think. A stepper is a simple positioner: open-loop, moves in discrete steps. The drive says "move 200 steps" and the motor does it—unless the load jams. Then nobody knows until the part comes out wrong.

A servo closes the loop with an encoder. The drive always knows where the shaft actually is. That's the difference between an industrial servo motor and a stepper in one sentence.

The question everyone asks is "which is cheaper?" The question they should ask is "what happens when the load jams?" Steppers lose position silently. Servos detect it and fault. For an axis with a human nearby or tight quality requirements, that difference is the whole story.

Cost-wise, a stepper package (motor plus driver) runs 30–50% below an equivalent servo. But servos hold up better at higher speeds and in overload. My rule: if the axis never jams and speed stays modest, stepper. Everything else, servo. And if you want Siemens at a stepper-like price point, look at the SIMOTICS S-1FL6 servo system (SINAMICS V90 drive)—it's their answer to machines that would've used steppers.

4. Stepper motor wiring: why does it trip everyone up?

Stepper motors have multiple coils—typically 4, 6, or 8 wires coming out. The two mistakes I've dealt with more than any other:

First, mixed-up coil pairs. You need the datasheet or a multimeter to identify which wires belong to which coil before connecting the driver. Guessing? Not ideal. Workable sometimes, but not ideal.

Second, ignoring bipolar vs. unipolar wiring. Six- and eight-wire motors can be connected several ways. Series vs. parallel changes torque and speed. Get it wrong and the motor runs weak, hot, or not at all.

Practical tip: download the wiring diagram before you order, not after you're standing there with six wires and a deadline. The diagram is in the datasheet. It is not in the box.

5. Permanent magnet or induction: how do I decide?

Siemens permanent magnet motors (like SIMOTICS T-1FW3) earn their keep in sustained low-speed, high-torque work—mixers, extruders, mill drives. They're smaller and more efficient than induction motors at the same torque, and they hold speed accuracy better.

But they need a VFD. No exceptions. You can't DOL-start a PM motor. So the purchase becomes a system: motor plus drive plus engineering time.

Induction motors are more forgiving. DOL or VFD, standard IEC/NEMA frame sizes, easy to repair. Per IEC 60034-30-1, efficiency classes run IE1 to IE4, and under EU Regulation 2019/1781, IE3 is essentially the floor for three-phase motors in the 0.75–1000 kW range. An IE4 induction motor captures most of the energy savings of PM at a fraction of the system cost.

The rule I use: if a standard IE3/IE4 induction motor fits the duty cycle and space, save the money. If you're fighting for torque density or energy cost at low speed, a PM motor pays for itself.

6. Is Siemens worth the premium?

For our plant, yes—most of the time.

ABB, WEG, and Nidec make solid motors. We've bought them. But our plant standardizes on Siemens drives. Matching Siemens motors to Siemens drives means fewer compatibility questions, cleaner documentation, and one supplier to call when something goes wrong. Operations loves the reliability. Finance tolerates the price tag.

The vendor failure in March 2023 changed how I think about backup planning. A critical conveyor motor failed with no spare in stock. One distributor said "probably two weeks." Another had the exact motor in a warehouse and promised five days—for $400 extra in freight. I paid it. Not because I wanted to. Because a line shutdown costs us roughly $2,000 an hour. That $400 was cheap.

Uncertain cheap is more expensive than certain expensive. In industrial motors, "probably" is the most dangerous word in procurement. Three things to verify before you hit send: stock. lead time. part number. In that order.

7. How do I decode a Siemens motor part number?

Siemens order numbers are dense. A 1FK7 servo order code like 1FK7032-5AF71-1FH0 breaks down roughly as: series, frame size, length, winding, and encoder/brake options.

I'm not going to pretend I read them from memory—I've ordered dozens and I still don't. What I do: pull up the catalogue selection table, copy the exact order code, and triple-check the free text on the PO.

That habit saved us in Q1 2024. Maintenance asked for "the same motor as last time." Same part number? No—the encoder had changed between revisions. One digit different. Cost if we'd guessed? Reinstallation labor plus another week of downtime.

8. What do these motors actually cost?

Prices vary with options, so treat these as ranges from distributor quotes over the past 18 months—not fixed prices:

• Small 1FK7 servo (0.4–0.75 kW): $800–1,800 depending on encoder, brake, and cable.
• 1.5 kW induction motor, IE3: $400–900 list.
• 7.5 kW induction motor, IE3/IE4: $1,500–3,000.
• Stepper motor + driver kit: $150–600, typically not Siemens-branded.

The catch: actual Siemens pricing comes through distributors, based on volume and availability. As of early 2025, lead times on some servo sizes are 8–12 weeks. So the first question isn't "what's the price?" It's "is it in stock?"

The 1FK7 catalogue PDF is free on Siemens Industry Online Support. Skip the third-party upload sites—half are outdated.