277 V Question

[Jimmy7]

I'm looking at a drawing that states that a panel is Volts: 480Y/277, Phase 3, Wires 3 (Image below). I didn't think you can get 227V from a 3 Phase 3 Wire system, correct? Shouldn't this be a 3 phase, 4 Wire system?

 

[Rock86]

Are you looking at shop drawings or engineer design drawings?

 

[Jimmy7]

Engineer design

 

[bwat]

Couldn't it be possible that the system is 480Y/277, 4-wire, but this panel isn't expecting to have or use the neutral from the system, so that's why it's listed as 3 wire? There wouldn't be the ability to actually have 277 loads, but you'd have 277 from any phase to EGC. This is to differentiate it from panel that is ok to be connected to a 480 ungrounded or corner grounded delta system.

 

[Jimmy7]

On the schedule for this panel all of the loads are 3 phase motors, except for a motorized damper which is listed as 277v.

 

[infinity]

The system is 480Y/277, when your loads are only 480 there is no neutral in the panel feeder. However the 277 volt circuit requires a neutral.

 

[roger]

The drawings are incorrect.

Roger

 

[Strathead]

Couldn't it be possible that the system is 480Y/277, 4-wire, but this panel isn't expecting to have or use the neutral from the system, so that's why it's listed as 3 wire? There wouldn't be the ability to actually have 277 loads, but you'd have 277 from any phase to EGC. This is to differentiate it from panel that is ok to be connected to a 480 ungrounded or corner grounded delta system.

I am pretty sure the code requires the neutral to be brought to any panel in a 480/277 Wye system. Don't have my code book in front of me so it could be just services.

 

[texie]

I am pretty sure the code requires the neutral to be brought to any panel in a 480/277 Wye system. Don't have my code book in front of me so it could be just services.

Just services.

 

[bwat]

I am pretty sure the code requires the neutral to be brought to any panel in a 480/277 Wye system. Don't have my code book in front of me so it could be just services.

No, as texie said, that's only true for services.

 

[Jraef]

It’s done all the time in MCCs where the loads are mostly motors. That 4th busbar and the cable to feed it are expensive for something you will never use. But if the SERVICE is 4 wire, then the reference voltage to ground is going to be 277V no matter where you read it. That becomes important for things like VFDs that are designed around a grounded wye system. So it’s valuable information to know it is a 480Y277 source, even if you don’t bring the neutral out to the distribution equipment.

In your case, because you have a 277V load you need that 4th wire. But if it is just one small load, you might just get a small transformer.