Can Duet be wired for NEC Class 2?

[drd505]

I'm designing a product around the Duet 3, and am looking for resources on how to build to NEC Class 2 specification. My understanding of this spec is that the output of the PSU should be limited to 100W with a fuse of 8A or less; the initial design assumes 24V in to the Duet. It will be driving 2x NEMA 23 and 2x NEMA 17 steppers. The NEMA 23s will draw over 4A at 24V, which would not leave any power for the NEMA 17s to keep the output under 100W (there will also be one heater driven from the Duet, so, it's even worse). Could Class 2 be satisfied if the stepper outputs of the Duet are fused? Or could the system be driven by 12V, allowing the 8A fuse to be used on the Vin to Duet? Or do the stepper drivers have on-board overcurrent protection that is Class 2 compliant?

Any thoughts or suggestions are welcome.

Thanks!

[dc42]

@drd505 the Nema 23 motors will draw far less than 4A from 24V even if they are rated at 4A and you set the current to 4A. See https://duet3d.dozuki.com/Wiki/Choosing_the_power_supply.

[rjenkinsgb]

@drd505 said in Can Duet be wired for NEC Class 2?:

My understanding of this spec is that the output of the PSU should be limited to 100W with a fuse of 8A or less;

The limit is 100VA; so with DC, at 24V the current is only a fraction over 4A per power supply.

It would be 8A with a 12V PSU.

The current cannot be exceeded even under fault conditions & the PSU itself must be certified for that use.

You can use more than one appropriate PSU for separate parts such as electronics, motors, heaters etc. as long as the PSUs are not paralleled, though it appears OK to use a common negative with separate positive feeds.

Or you can use a larger PSU and a protection module that splits it to a number of separate Class 2 rated outputs.

More info in this article:
https://www.pulspower.com/fileadmin/global/common/Print/White_papers/an45_en.pdf

[drd505]

@dc42 Cool cool, I hoped the ability to set current on the stepper outputs may be sufficient for Class 2, sounds like this is the case; thanks for elaborating and for the wiki link. We will be using a Meanwell PSU (LRS-350-24).

[drd505]

@rjenkinsgb I believe the PSU is CE listed, Meanwell LRS-350-24; I hadn't considered using multiple PSUs, thanks for the link to the protection module.