277V Panel Circuits

[The Great Sarducci]

Hey all,

I'm currently in the process of designing a 480V enclosure, which contains several heat-generating components (motor VFD drives, motor contactors, etc.). Long story short, the enclosure needs cooling; and am therefore going to be putting a couple of fans on the door. One of my co-workers said that he thought that I should go with a 230V/1PH unit. However my thoughts were against this because this would require installing a transformer. We are limited on space for fuses, so although I could get a 480V/3PH unit, it's going to be hard to do. So what I then suggested was finding a fan that would run on one leg of 480 as a 277V fan motor. Whether or not anyone sells one, I have yet to look into. But on to the reason for my post... As soon as I suggested a 277V unit, my co-worker immediately came back with; "Oh..you can't do that. You're never allowed to have single phases over 150V to ground as it's own circuit inside of an enclosure". This at first puzzled me a bit because I am more than familiar with 277V lighting. But he explained to me that 277 is okay only when run outside of a panel, but inside a panel is a big no no because code will not allow it due to it being greater than 150V to GND. Is this actually true, or a load of bull? Also, I'd like to add that I'm only concerned with low-voltage (600V and lower) applications. I know that obviously no such rule would ever apply to medium voltage panels/enclosures.

 

[tommydh]

May I suggest running a single 120v circuit from a near by source to power your fans. As long as the conductor insulation meets the same as on the ones from the 277/480 panel it is ok to do. They make enclosures that have these provisions in them already I'm sure. If you can get an integrated Cabinet with your 480/277 panel a transformer and 208/120 in same cabinet but separate compartments you can use 120v in your 480 panel for fans
I think the majority of forced inducted cooling set ups I have sen had the fans either in the top or bottom corners of the enclosure oor in the sides below any area with breakers.

 

[augie47]

I know of noting in the NEC that would prohibit you from using 277v fan motors. That said, keep in mind, as an assembly the unit might be required by the AHJ to carry a NRTL listing (such as UL) and there may well be some rules in UL508 or pertinent listing rules that would not allow the 277v.

 

[kwired]

I know of noting in the NEC that would prohibit you from using 277v fan motors. That said, keep in mind, as an assembly the unit might be required by the AHJ to carry a NRTL listing (such as UL) and there may well be some rules in UL508 or pertinent listing rules that would not allow the 277v.

Since he says he is designing this, unless he is a certified panel shop making listed panels, it probably is only being made to NEC requirements. I would hope he would have mentioned in OP if it were being designed to UL508 if he actually were making such panels and had a question on the standard.

by The Great Sarducci...

But on to the reason for my post... As soon as I suggested a 277V unit, my co-worker immediately came back with; "Oh..you can't do that. You're never allowed to have single phases over 150V to ground as it's own circuit inside of an enclosure". This at first puzzled me a bit because I am more than familiar with 277V lighting. But he explained to me that 277 is okay only when run outside of a panel, but inside a panel is a big no no because code will not allow it due to it being greater than 150V to GND. Is this actually true, or a load of bull?

I think it is a load of bull. All your three phase circuits in the panel are already over 150 V to GND.

Do you not have any lower voltages for controls in the panel? Even a 24 volt control circuit might be able to power a fan for this without going too overboard with the needed control transformer VA. Fuses - you very well will need some for this fan even if it is a 480 volt fan.

 

[The Great Sarducci]

Since he says he is designing this, unless he is a certified panel shop making listed panels, it probably is only being made to NEC requirements. I would hope he would have mentioned in OP if it were being designed to UL508 if he actually were making such panels and had a question on the standard.

- My apologies for not including a little more info on the standards which we are going by on this job. There are actually 3 standards we commonly use in our designs. The 1st is of course, the NEC. The second is the NFPA 79 (which also had nothing in it that I could find on prohibiting inner-panel 277V use). Lastly, and as you mentioned above; we do use the UL508. The reason being that we actually have a panel shop and build all of our panels in-house (panels are built for customized test machines however, and not for commercial/industrial sale as standalone products). To the point of the UL508, I have not done much digging into it for this job, as the design is very similar to previous jobs which were highly based in this standard. But it would be worth seeing if maybe something in the 508 is what my co-worker was referencing. He is more familiar at least with this particular standard than I am.

I think it is a load of bull. All your three phase circuits in the panel are already over 150 V to GND.

- Indeed part of the reason in which this whole idea confused me so much. Wherever there is 480/3Ph power, there are also line potentials of 277V to ground. At least now I know that I'm not thinking crazy thoughts.

 

[The Great Sarducci]

Do you not have any lower voltages for controls in the panel? Even a 24 volt control circuit might be able to power a fan for this without going too overboard with the needed control transformer VA. Fuses - you very well will need some for this fan even if it is a 480 volt fan.

- I've actually used 24VDC fans on a number of projects, and normally consider them first. The problem in this case; I'm limited to a 40A PWS. and have so many control circuits, that there isn't much capacity left over. Since the 24V models typically pull several amps for the larger cfm ratings, I wouldn't have enough juice available without getting too close to maxing out the supply. Haven't used a 24VAC system in anything for over 5 years. But it could be a point worth looking into since a dedicated XFMR just for the fan/tstat circuit would be fairly inexpensive. Anyway thanks for the info.

 

[The Great Sarducci]

May I suggest running a single 120v circuit from a near by source to power your fans. As long as the conductor insulation meets the same as on the ones from the 277/480 panel it is ok to do. They make enclosures that have these provisions in them already I'm sure. If you can get an integrated Cabinet with your 480/277 panel a transformer and 208/120 in same cabinet but separate compartments you can use 120v in your 480 panel for fans
I think the majority of forced inducted cooling set ups I have sen had the fans either in the top or bottom corners of the enclosure oor in the sides below any area with breakers.

- So as it turns out, I may end up needing 120V for something else in the panel anyway. So this may actually be a good option. Thanks.

 

[The Great Sarducci]

I know of noting in the NEC that would prohibit you from using 277v fan motors. That said, keep in mind, as an assembly the unit might be required by the AHJ to carry a NRTL listing (such as UL) and there may well be some rules in UL508 or pertinent listing rules that would not allow the 277v.

- As I also just noted in my reply to kwired; we (my company) do use the UL508 in our designs since we build all of our own panels. Since this panel is fairly redundant (component wise) to past projects; I haven't cracked it open much for this project. But your suggestion is definitely a possibility, and I'll have to look into it to see if the 508 does in fact call out some odd rules when it comes to L-N / L-GND voltages when used for dedicated loads inside the panel. Thanks for your reply & the info.