UL regulations for smaller NEMA stepper motors (23 and 34 sizes) 2

[kjoiner]

Hello,

I am considering some smaller stepper motors for an application. All our equipment is certified to UL 751 and FCC part 15. I would like to find out if stepper motors fall into a category that requires UL testing. I have asked the lab that performs our testing but they are not familiar with stepper motors.

I have a few reasons to ask:
1. The power supply for steppers is typically 48 VDC. This falls under the 60 VDC limit but because steppers operate using pulsed DC, I am concerned they fall into the interrupted DC category which limits voltage to 24.1 VDC for frequencies of 10-200 Hz.
2. Stepper motors have a lot of heat gain. The ones I am currently bench testing reach 120°F
3. I am not finding many stepper motors that have either UL listed or UL recognized status. Most carry CE but that is not relevant to US testing requirements according to our lab.

By my term "limits" in 1 I am referring to the threshold which requires testing.

Has anyone gone through UL testing for products with stepper motors? Did you encounter any obstacles?

Thanks,

Kyle

 

[Gr8blu]

Try contacting the vendor from the link. I see they have NEMA 23 and 24 motors with UL listing.

https://www.applied-motion.com/products/series/ul-recognized-stepper-motors

Converting energy to motion for more than half a century

 

[btrueblood]

Oriental Motors also has UL listed steppers and drives.

 

[tygerdawg]

I could be wrong, I usually am...
However...

UL approval is not a regulation as in the sense of what OSHA has been authorized by Act of US Congress to promulgate. I am not aware that Underwriter's Laboratory will chase you down and issue a citation and assess a penalty for deploying a product to the marketplace that does not have something called "UL approval."

A device that meets UL approval will help lawyers make a case in the event there is an issue. But is it mandatory? The answer to that question depends upon the legal team of the corporation. Given how Corporate Legal Teams think and their ability to accept risk, you might can guess the answer to that.

Don't be confused by the difference.

TygerDawg
Blue Technik LLC
Manufacturing Engineering Consulting

http://www.bluetechnik.com

 

[FacEngrPE]

The legal side of UL is that it is one of a number of NRTL's recognized by OSHA. The linked page on OSHA's site indicates which classes of products require some kind of NRTL testing, i did not see stepper motors, but it is possible that stepper motors could be included in a machine that requires a NRTL listing, that might generate a requirement for a component listing.
OSHA's Nationally Recognized Testing Laboratory (NRTL) Program

This is a stepper motor with a UL Component listing.

 

[kjoiner]

Hello,

Thank you for all of the responses. Oriental Motor and Applied Motion are two of the vendors I am investigating.


@tygerdawg "UL approval is not a regulation as in the sense of what OSHA has been authorized by Act of US Congress to promulgate. I am not aware that Underwriter's Laboratory will chase you down and issue a citation and assess a penalty for deploying a product to the marketplace that does not have something called "UL approval."

We receive an Authorization to Mark (ATM) for our equipment that allows us to put the UL approval on our labels. Our testing lab has inspectors that visit typically once a quarter and they compare items we used in production against our listing report. We then receive a findings report that lists any discrepancies. They have different levels of deviation. It's never happened but I assume that with a serious enough deviation, they could revoke our ATM. At that point, if we were to continue marking our equipment, that probably when the lawyers would get involved. Again, that's never happened with us.

Kyle

 

[jraef]

UL is not required, but an NRTL listing is in most places in the US. So it becomes an issue for someone installing equipment under a permitted project that will be inspected by the local AHJ (Authority Having Jurisdiction). It’s not something to ignore.

You will find that steppers will not be “listed”, they will be “Recognized” (showing that backward UR symbol), which is different in that a recognized component MUST be used in conjunction with something else, in this case the stepper driver, and the combination must then be “added to the procedure” in terms of getting the entire assembly listed. That also then means you cannot use a stepper from one supplier and a driver from another, because they will not have been recognized together. Just be aware of that little quirk.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[kjoiner]

Hello,

Jraef - thank you for the insight regarding use of stepper motors and their drivers. That's a piece of information I did not have before. I was hoping we could mix and match motors and drivers to open up our supply chain options. As you mention, they are part of a system. Along those lines, we have components that are UL listed and UL recognized. Either way, because they are part of an overall products, they must be tested in context with the entire system.

We will continue the search for motors and drivers that have UL and CSA to simplify the overall testing process.

Kyle

 

[btrueblood]

Some 10 years ago we got our device with a stepper motor through NRTL testing, using the vendor I suggested above. Our original device used a non-UL rated stepper, and the test lab made us test to the UL motor standard (1004?), which includes a locked rotor test, where the winding temperature was measured with the rotor locked and full amperage applied...we cooked the motor pretty quickly (insulation burnt). A good driver (one that would pass the UL test) would detect the winding temperature rise (rise in winding resistance) and shut itself off*, or the motor would be built so that the winding temperatures did not rise above the insulation rating. Funny enough, the other manufacturer listed above is the one who sold us the original motor/driver - good to see they offer UL rated versions now.

*or reduce amperage. Or it might detect loss of rotor motion and fail safe from that alone.

 

[kjoiner]

@btrublood,

That's a good point. We also use AC gearmotors in one of our machines and even though the motors carry UL, our lab still required lock rotor tests when we added them to our listing report. That also reinforces the need for parts with UL ratings.

Kyle

 

[btrueblood]

To be clear...we could probably have worked around the problem without a UL rated motor/driver combo. But, it would have been expensive (due to added testing), and we would probably have had to do repeated tests (i.e. recurring expenses) of whatever temperature control method we chose to prove it continued to work.

 

[kjoiner]

@btrueblood,

Totally agree. We do have some custom components that require annual testing to keep them in our listing report. It does get expensive. Sometimes I feel like it's a moving target.

Kyle

 

[kjoiner]

Hello,

I've been doing a lot of searching for UL recognized stepper motors and drives over the past couple of weeks. I've found some but lead times are extending way out into 2023. Some manufacturers carry drives that are UL recognized but their motors are not - for others its vice versa.

This morning, while seraching on the Hayden Kerk site, I found this comment:

https://www.haydonkerkpittman.com/learningzone/faq/stepper-motors

quote from their site:

"Are your motors UL, CSA, or CE approved?-"
"No, due the low voltage at which they operate UL, CSA, or CE are not required. However, many systems that have these approvals utilize our motors and ultimately get approved as a complete system."


I do expect to retest our machine with any new components but not having to find a combination of motor and drive that are UL and CSA recognized will help a great deal. What are everyone's thoughts on this information?

Thanks,

Kyle

 

[btrueblood]

We tried that line on our NRTL, they said no, every part in the device has UL/CSA recognition, or it has to be independently tested to meet UL/CSA requirements. It's a motor, so it gets tested to UL 1004 - which our original motor failed. Again, find a good driver that includes temperature control for the motor and you can likely pass the test, but the NRTL will need to do the test, and they may require you to functional tests of the product to show continued compliance to the spec.