Siemens Motor Frame Size Chart Lessons From a Real 5HP Replacement (VFD Sizing Included)

It Started With Smoke on a Friday

At 2:40 on a Friday afternoon last October, Ray appeared in my doorway with the look that means production is about to get complicated. He held up his phone. “Motor on the #4 spindle coolant pump,” he said. “It’s dead. Actually it smoked, then it died. We need another 5 hp Siemens motor.”

I’m the office administrator at a 60-person machining shop, and “we need another motor” eventually lands on my desk. Since 2020 I’ve handled most of our MRO buying—maybe 150 purchase orders a year, give or take, I’d have to check the system. I manage the vendor relationships, chase the invoices, and make sure the maintenance team isn’t waiting on me. That Friday, they were.

I Assumed 5 HP Was 5 HP. That Was Wrong.

When I first started buying motors, I honestly assumed the horsepower number was the entire specification. If it said 5 hp, a new 5 hp motor would bolt on and run. It took about three hours of motor research to realize how naive that was.

Ray sent me a photo of the old nameplate. It showed a Siemens three-phase motor, 5 hp, 460 V, 1745 rpm. Then he said the phrase I now hear in my sleep: “Check the frame. It’s a 184T frame. Don’t just buy any 5 hp motor, or the bolt holes won’t line up.”

Frame size. The part I’d never heard of.

I opened the Siemens motor frame size chart for the first time and realized it isn’t just one dimension—it covers shaft height, shaft diameter, keyway size, mounting hole pattern, and overall length. Two motors with the same horsepower and speed can be physically different sizes depending on the frame series, enclosure, and mounting style. That was my first lesson: never assume the motor is defined by its HP rating alone.

I also learned something else that week. A surplus listing for a “compatible 5 hp motor” popped up in my search results. It was roughly $460 less than the new Siemens motor from our regular distributor. I want to say $460, but don’t quote me on that; the point is it looked like a deal. The listing said “same HP, comparable dimensions,” but there was no data sheet and no proper frame designation.

I went back and forth for about two hours. The surplus motor would have saved us money on paper. But with a machine down, the lowest total cost isn’t the one with the lowest sticker price—it’s the one that fits and runs the first time. We needed a documented 184T frame, not “probably close enough.”

The “D-90441” Line Was Not a Model Number

Here’s where the search got weird. I tried looking up the old motor by the information Ray gave me, and I kept seeing the string “siemens d-90441 motor” in results. I assumed D-90441 was some kind of model code. I searched it, compared photos, and got nowhere.

Finally, I called the electrical distributor we use. The technical support person asked me to read the nameplate top to bottom. When I got to the bottom, she laughed—kindly, but she definitely laughed.

“D-90441 isn’t a motor model. It’s an address. It means Siemens AG, 90441 Nürnberg. Nuremberg, Germany. That’s the plant address that appears on a lot of Siemens motor nameplates.”

I should have caught that sooner. On many Siemens motors, the nameplate includes the manufacturer’s location as part of the standard marking. Searching “siemens d-90441 motor” was a dead end because that line alone doesn’t identify the motor. The useful information—catalog number, frame, voltage, current, speed, and duty rating—is printed in the rows above that address. Once I understood that, I stopped trying to order a “D-90441 motor” and started looking for the actual type designation and frame data.

The distributor sent us a Siemens motor frame size chart reference, confirmed the 184T dimensions against the old nameplate, and quoted us a new motor that matched. It was more expensive than the surplus listing. It was also the right one.

What Size VFD for 5hp Motor?

The other question that came up that afternoon was about the drive. Ray wanted to add a variable frequency drive while we were replacing the motor so the coolant pump could run at adjustable speed. He knows motors and mechanical systems far better than I do, but even he paused: “What size VFD for 5hp motor? I think we need a 5 hp drive, but I want someone to confirm the amp rating.”

The answer from the distributor stuck with me:

A VFD is usually sized to the motor’s nameplate voltage and full-load current. In most constant-torque applications, you match a 5 hp motor with a 5 hp VFD at the same voltage. For a 5 hp, 460 V three-phase motor, the motor full-load current will be around 7.6 A per standard reference tables. The VFD’s continuous output rating needs to be at least that number. If the motor were wired for 230 V, the current doubles to roughly 15.2 A, and the VFD would need to be rated for that instead.

So the practical rule is: don’t oversize or undersize by guessing. Match the horsepower, verify the output current rating against the motor nameplate, and confirm the supply voltage matches the motor connection. In our case, a 5 hp VFD rated for 460 V gave us enough continuous output current, and it didn’t cost us a bigger drive we didn’t need.

I’ll admit, I was a little nervous asking that question. I’m not an electrical engineer. But the person on the phone answered it the same way I like vendors to answer my calls: no condescension, just a clear explanation and a recommendation.

Meanwhile, a Linear Actuator Controller and a Small Stepper Motor

While I was waiting for the motor quote, two smaller requests landed on my desk. Ray asked for a replacement linear actuator controller for the damper louver on the roof unit, and he needed a small stepper motor for a parts-indexing fixture he was building on the side. Both orders were small—probably under $300 combined. I almost sent them to a different supplier to keep the main purchase “clean.”

Instead, I added them to the same conversation with the distributor. That turned out to be the right call. The rep didn’t treat the small-items request like a nuisance. She asked what voltage the linear actuator controller needed, what control signal we were using, and what frame size of small stepper motor we wanted. We confirmed the details, and both items went into the same shipment.

I’ve learned not to assume a supplier will care about a $200 order. In my role, I’ve seen vendors who barely respond once they realize the order is small. But small orders have a way of growing—today’s $200 request can turn into next year’s $2,000 order. Good service shouldn’t depend on order size. It’s one reason we kept that distributor.

What I’d Do Differently Now

The motor arrived Tuesday morning. Ray and his helper installed it that day, and machine #4 was cutting chips by Wednesday. The total downtime was longer than any of us wanted, but it could have been worse.

Looking back, the experience changed how I buy motors and drives. Now I ask for the nameplate photo first. I look for the frame designation, not just the horsepower. I check the catalog number and the address line without assuming it’s a model number. And I don’t hesitate to ask “what size VFD for 5hp motor?” or any other question that makes me sound like a non-engineer—because the engineers on the other end of the phone would rather answer questions than process a return.

If there’s one thing I want any other office buyer to take from this story, it’s this: the Siemens motor frame size chart exists for a reason. A motor’s nameplate is not paperwork—it’s the complete specification. The frame determines whether it fits, the electrical data determines whether it runs safely, and the people who help you get those details right are worth more than any discount.

Now I check the frame first. Then the price. That’s it.