7 Questions About Siemens Motors That Are Worth Asking (Before You Buy or Specify)

I've been inspecting and specifying industrial motion components for close to a decade. Siemens motors come up a lot—probably because they're a default spec for a lot of automation systems. But default doesn't mean simple. Here are the questions I keep hearing, and the answers I usually give.

1. What's the difference between buying from an authorized Siemens motor dealer vs. a general distributor?

I asked a procurement friend this years ago. He assumed "a motor is a motor." That assumption cost his team about three weeks of downtime when a replacement unit didn't match the wiring diagram—turns out the distributor had sold them a parallel-wound motor when the VFD needed a series configuration.

An authorized Siemens motor dealer isn't just a reseller. They have access to the Siemens motor catalog with proper cross-reference tables, correct data sheets, and—importantly—warranty support that doesn't bounce between manufacturers. The pricing might look higher on paper, but if you factor in the support calls and the risk of receiving a wrong spec, the dealer route usually wins.

At least, that's been my experience with medium-to-large automation projects. For a simple replacement where the motor tag is readable and the application is standard, a general distributor might be fine. But for anything with a VFD or a custom wind, I'd stick with an authorized source.

Note: This reflects my understanding as of early 2025. Distribution agreements change, so verify current authorized lists directly with Siemens.

2. I see references to "Pete Jackson Gear Drives" online—what's the story there?

You're probably asking about the search term 'what happened to Pete Jackson gear drives.' I ran into this during a research session. Pete Jackson was a brand known for aftermarket gear reduction units, largely in niche automation and custom machinery. They had a solid reputation in the '90s and early 2000s.

The short version: the company was acquired and the brand was phased out around 2018. Their legacy products are still in service, but support and replacement parts have become inconsistent. If you're maintaining a system with a Pete Jackson unit, you're likely looking at retrofit options—often a Siemens gear reducer as a drop-in replacement with adapter plates.

I won't claim to be an expert on the acquisition details. But I've reviewed maybe 20 retrofit specs over the past four years, and the Siemens flender series gearboxes have been the most common replacement we see specified. Worth checking if you're maintaining older equipment.

I want to say the acquisition was by a larger European group, but don't quote me on that—verify through industry trade records.

3. I need a stepper motor diagram for a retrofit project. What's the best source?

This is one of those questions where the answer depends on what you're retrofitting. A stepper motor diagram isn't standard across all Siemens stepper motors—the pinouts and wire colors vary by series and by the drive they connect to.

What I've found reliable: the specific Siemens manual for the motor and drive pair. For example, the Siemens single motor module 6sl3120 manual includes termination diagrams for the power and encoder connections. It won't show you a generic "stepper diagram"—it shows you exactly how to wire that module to its compatible motors.

I learned this after a project where we used a generic diagram from a forum. The wiring was close, but the encoder phase alignment was off. That alignment issue cost us about four hours of troubleshooting and a rushed rewire. The manual had the exact diagram we needed—we just hadn't checked it first.

Put another way: the best stepper motor diagram is the one in the manufacturer's documentation for your specific module.

4. Are electric actuators linear worth the premium over pneumatic?

I had this debate with a plant engineer in 2023. He was convinced pneumatics were cheaper and simpler. On a straight purchase comparison, he was right—a basic pneumatic cylinder and valve is roughly 30–40% less upfront cost than a Siemens linear actuator with its drive.

But we ran a comparison for a packaging application that required repeatable position control across 50,000 cycles per year. The pneumatic system needed periodic cushion adjustments and had drift over temperature changes. The electric actuator held position within ±0.1 mm without intervention.

The hidden cost: the pneumatic system required about 15 hours of maintenance per quarter. The electric actuator needed maybe 2 hours. At $75/hour shop rate, that's a $3,900 annual difference. Over a three-year lifecycle, the electric actuator was actually cheaper.

That said, if your application is simple open/close with no position feedback and low cycle count, pneumatics are probably the pragmatic choice. The premium for electric makes sense when you need precision, data logging, or energy efficiency.

5. What's the most common mistake when specifying a VFD for a Siemens induction motor?

Assuming any VFD works with any motor. I know that sounds basic, but I've rejected three batches in Q1 2024 alone where the drive and motor weren't properly paired.

The biggest issue: output voltage and current ratings. A VFD rated for 5 HP doesn't automatically mean it can drive a 5 HP Siemens induction motor across all speed ranges. At low speeds, the motor draws higher current for the same torque. If the VFD can't supply that current continuously, you get overheating—or nuisance trips.

The Siemens motor catalog specifies the maximum permissible current for each motor at various speed/torque points. Matching the VFD to those curves is critical.

Also—and this is one I've seen cause a $22,000 redo—the cable length between VFD and motor matters. Long cables can cause reflected voltage spikes that damage the motor winding insulation. Siemens publishes maximum cable length guidelines for each drive series. Exceeding them without a output reactor is asking for a winding failure.

6. Should I buy a Siemens single motor module 6sl3120 as a spare, or just rely on the dealer's stock?

This depends on your tolerance for downtime. The 6sl3120 is a common module in the SINAMICS S120 lineup, and repair lead times can range from 2 weeks (if the dealer has it) to 8 weeks (if it needs to be ordered from Siemens).

I've seen a plant keep one as a critical spare for their most bottleneck machine. The cost was roughly $1,800 (as of late 2024 pricing). The downtime cost for that machine was about $4,000 per hour. In that context, the spare paid for itself in 27 minutes of avoided downtime.

But for non-critical applications or modules that are easily swapped between machines, stocking a spare might not make financial sense. The key is to calculate the cost of downtime vs. the cost of the spare plus the carrying cost over its shelf life.

Pricing was accurate as of Q4 2024. The market changes fast, so verify current rates before budgeting.

7. What's something about specifying Siemens motors that most people overlook?

Housing and coating compatibility. I probably sound like the quality inspector I am, but I've seen projects where the motor specification was perfect electrically—voltage, speed, torque—but the motor failed within six months because the housing wasn't rated for the environment.

A standard Siemens induction motor with an IP55 enclosure is fine for most indoor industrial settings. But if there's washdown, chemical spray, or high humidity, you need IP65 or higher, with the appropriate shaft seal and coating.

I reviewed a spec for a food processing line where the engineer specified standard gray cast iron motors. The environment required stainless steel or epoxy-coated housings. The spec change added maybe 15% to the motor cost but prevented a failure that would have stopped production for a full shift. Upgrading the specification increased customer satisfaction scores in their post-install audit—the plant manager specifically noted fewer unplanned cleanups.

What I'm saying: don't just check the electrical data sheet. Check the environmental data sheet too.