UL 508: Any Reason I can't supply a 60W 24VDC Power Supply from 2 legs of 480VAC?

[theColonel26]

UL 508: Any reason I can't supply a 60W 24VDC power supply from 2 legs of 480VAC?

Our MechE is asking, it is for a product I don't deal with. My first reaction was sure why not? it is like 1/8Amp at 480VAC. Then he was like, well is there anything in UL508 that says you aren't allowed to have an unbalanced 3pH load?

I can't find anything about this subject in the standard, but that doesn't mean it isn't there.

We have always used 3pH power supplies on that product, but we are having issues sourcing them, so they want to switch to a single phase.

 

[ndzied1]

It’s fine so long as
- the power supply is 508 listed
- you use proper branch circuit protection
- use properly sized/ rated conductors

 

[Rson]

I constantly use 3 phase 480 to 24VDC power supplies - usually 90W, but 60W isn't much different. Just make sure they are rated for the voltage input, they are UL listed, and you are using the right sized conductors.

They won't unbalance your load any more than a transformer will.

 

[Helliana]

There are single phase 480V power supplies on the market. I've personally used AB/Puls ones.

 

[Snyd1]

With such a small load you will not notice an imbalance great enough to effect anything. If there are other single phase loads it is common to even the single phase loads out between different legs. If this is the only one I would not worry.

Note: I am not aware of a section in UL that covers this, but does not mean there is not one. Some plants with 240V and a high leg have no choice but to put all single phase loads on the two phases available

 

[Jim3846]

If your worried about unbalanced current on 3 phase , then take measurements and see if it is unbalanced.

 

[jraef]

If anyone were concerned, control power transformers would be forbidden…

Fuggedaboudit…

 

[rupej]

I can assure you that UL is not concerned about the plant's utilities.

 

[g.mccormick]

If anyone were concerned, control power transformers would be forbidden…

Fuggedaboudit…

You cant use a control power transformer in a 508 panel?

 

[theColonel26]

You cant use a control power transformer in a 508 panel?

No he was saying if I logically couldn't connect a DC power supply to 2 legs, then it would follow that you couldn't do that with a transformer either.

Which is obviously not true.


I shall admit, my question was dumb but my MechE's question got me questioning my own reality lol

I used to supply transforms and Power supples from 2 legs all the time, but that wasn't at a 508 Shop.

 

[JMBistodeau]

1606-xlp90e-2


480 VAC 1 PH input.


Follow table 35.1 in UL508A for branch circuit protection.

 

[I_Automation]

If anyone were concerned, control power transformers would be forbidden…

Fuggedaboudit…

Single phase in VFD's, most smaller robot controllers are single phase that control all 6 axis', almost all heaters.....


Quite a few things can be single phase line voltage - it's up to us to make sure there isn't a phase imbalance by wiring them all A to B.

 

[theColonel26]

Ok ok I admit it was a really stupid question I just had a brain **** lol