Did i say it wrong??

[brother]

Ok, I may have made a mistake, but there is this system im working on, its 3 phase and 1 ground, NO neutral. 277 volts to ground, and 480 volts phase to phase.

I told someone this was a '3 phase 4 wire' 277/480 volt system. Did i say it WRONG??, because there is NO neutral so they would not be using the 277 volts on this system. Also you do count the ground in your system right?? thats why i said 4 wire.

 

[iwire]

Ok, I may have made a mistake, but there is this system im working on, its 3 phase and 1 ground, NO neutral. 277 volts to ground, and 480 volts phase to phase.

I told someone this was a '3 phase 4 wire' 277/480 volt system.

Well it would be 480Y/277 volt system.

The fact you have 277 to ground suggests the system does originate from a grounded Y transformer even if there was no neutral present at the panel.

Also you do count the ground in your system right?? thats why i said 4 wire.

I would.

Check out this NEMA chart

 

[220/221]

I would call it 480, 3 phase, 3 wire

..........more commonly known as 483 phase 3 wire


I'd leave out the 277 because without the neutral, you can't use it.


Receps and SO cord count the ground but this is a system. A ground wire isn't necessarily present.

 

[infinity]

I agree with Bob this is a 277/480 Wye system. A 3 phase, 3 wire, 480 volt system would not have 277 volts to ground.

 

[Jim W in Tampa]

Ok, I may have made a mistake, but there is this system im working on, its 3 phase and 1 ground, NO neutral. 277 volts to ground, and 480 volts phase to phase.

I told someone this was a '3 phase 4 wire' 277/480 volt system. Did i say it WRONG??, because there is NO neutral so they would not be using the 277 volts on this system. Also you do count the ground in your system right?? thats why i said 4 wire.

By system not sure what your including.You have 277 available but not till your neutral is there.I would not say i have 277/480 3 phase unless i have all 3 phases and neutral.Based on what you called it someone might buy equipment that needs all of it.

 

[iwire]

Jim D. posted this a while ago in another thread but it is worth a look here.

The preferred ANSI method is:

120/240 single phase

208Y/120 three phase

240/120 three phase

480Y/277 three phase


Supply systems are listed at the nominal voltages listed in the NEC, 120, 208, 240, 480, and 600V.

Motors are listed at utilization voltages of 115, 200, 230, 460, and 575V.

Connecting types of devices like lamp holders and fuse holders are listed at a maximum voltage of 125, 250 and 600V.

Plugs and receptacles are listed based on their specific configuration.

 

[Smart $]

Also you do count the ground in your system...??

No, IMSHO.

The 4th wire may be the neutral of the "system", and the means by which the system is grounded, but if it is not present at the panel, it does not count... therefore 480 3? 3W.

 

[infinity]

How can you have 277 volts to ground on a 3 phase 3 wire system? If it were corner grounded it would be 480 volts to ground on two phases, if it were ungrounded it would have 0 volts to ground on all phases. In order to get 277 volts to ground it would have to be connected to a 480Y/277 volt system.

 

[iwire]

IMO we have two different things being talked about.

1) The voltage system supplying a feeder

2) The feeder or branch circuit itself.


IMHO what Brother describes is a 480 volt three phase three wire feeder supplied from a 480Y/277 system.

(Yeah I changed my mind about counting the ground:grin: )

 

[Smart $]

How can you have 277 volts to ground on a 3 phase 3 wire system? If it were corner grounded it would be 480 volts to ground on two phases, if it were ungrounded it would have 0 volts to ground on all phases. In order to get 277 volts to ground it would have to be connected to a 480Y/277 volt system.

You are correct... when talking about the "system".

However, at the panel with no neutral, fed from that system, it may be 277V to ground, but you don't count the ground as a wire. You can't say it is 277V line to neutral because there is none.

 

[infinity]

IMO we have two different things being talked about.

1) The voltage system supplying a feeder

2) The feeder or branch circuit itself.


IMHO what Brother describes is a 480 volt three phase three wire feeder supplied from a 480Y/277 system.

(Yeah I changed my mind about counting the ground:grin: )

I agree, this would be a typical feeder to the primary side of a 480-208Y/120 transformer in a commercial building. But that doesn't change the fact that it's fed from a WYE system. So the real question is are we describing Bob's #1 or #2?

 

[charlie b]

I disagree with everybody on this one. :wink: :roll: But much depends on what you mean when you say the "system" has no neutral. If, for example, you are only dealing with a distribution panel, and somewhere upstream of that panel (in an area you are not working with) there is a neutral, and if it is part of a "grounded AC system," then I will withdraw my disagreement.

However, if there really is no neutral in this system, then it is incorrect to say that the voltage to ground is 277 volts. It might be 277, or 27.7, or 2770. The power you are using might have originated from a three phase transformer with a delta wound secondary, and that secondary might have neither a corner nor a center tap connected to planet Earth.

So I will throw this back to the originator: what do you really know about the "system"?

 

[brother]

I disagree with everybody on this one. :wink: :roll: But much depends on what you mean when you say the "system" has no neutral. If, for example, you are only dealing with a distribution panel, and somewhere upstream of that panel (in an area you are not working with) there is a neutral, and if it is part of a "grounded AC system," then I will withdraw my disagreement.

However, if there really is no neutral in this system, then it is incorrect to say that the voltage to ground is 277 volts. It might be 277, or 27.7, or 2770. The power you are using might have originated from a three phase transformer with a delta wound secondary, and that secondary might have neither a corner nor a center tap connected to planet Earth.

QUOTE=charlie b][So I will throw this back to the originator: what do you really know about the "system"?

Ok, All i know is that this is from a disconnect to a building (the feeders), and i do believe it also supplies a transformer(im assuming because I know they got lights in there and maybe a desk top compter) in the building that step it down to 208/120. I know when i told the person that i did specifically also say its just 3 hots and 1 ground, no neutral. So im sure they got the gist of what i was saying.


So it looks like the proper way to say this is just " 480 3 wire" however, would not the transformer that step it down , would not the ground (primary)and neutral (from the secondary side) be bonded together?? just trying to learn here. I wont actually know the full story on if the transformer is there without actually looking in this small building/trailer

 

[jim dungar]

We must remember that most of the electrical world use phrases and terms that are highly context sensitive. We bring most of our confusion on ourselves by not providing all of the details (we try to use the fewest words possible).

From what I can tell, the OP has a 480V 3Ph 3W circuit fed from a 480Y/277V 3Ph 4W system.

 

[Smart $]

Ok, All i know is that this is from a disconnect to a building (the feeders), and i do believe it also supplies a transformer(im assuming because I know they got lights in there and maybe a desk top compter) in the building that step it down to 208/120. I know when i told the person that i did specifically also say its just 3 hots and 1 ground, no neutral. So im sure they got the gist of what i was saying.


So it looks like the proper way to say this is just " 480 3 wire" however, would not the transformer that step it down , would not the ground (primary)and neutral (from the secondary side) be bonded together??

Possibly and probably, but I do not believe it is required... at least not directly. The transformer secondary can be connected as, and usually is, a separately derived system. It's neutral, if it exists and is required to be grounded will be grounded to a GES. AFAIK, there is no requirement that it be the same GES as the primary, or an EGC be carried from the primary. Yet in all likelyhood, at least one of the required electrodes for grounding will be mutually inclusive, i.e. electrically the same electrode... such as structural steel or water supply pipe.

 

[brother]

Possibly and probably, but I do not believe it is required... at least not directly. The transformer secondary can be connected as, and usually is, a separately derived system. It's neutral, if it exists and is required to be grounded will be grounded to a GES. AFAIK, there is no requirement that it be the same GES as the primary, or an EGC be carried from the primary. Yet in all likelyhood, at least one of the required electrodes for grounding will be mutually inclusive, i.e. electrically the same electrode... such as structural steel or water supply pipe.

What does AFAIK mean?? also if its not required to be bonded would not this create a 'potential' between the transformer frame and the other metal thats suppose to be grounded in this building???

by the way this building is just a small type trailer that is just seperately sitting in front of the other building. This has got be bonded in my opinion

 

[iwire]

What does AFAIK mean??

As Far As I Know

also if its not required to be bonded would not this create a 'potential' between the transformer frame and the other metal thats suppose to be grounded in this building???

It would if it was not bonded but by the time you apply all the NEC rules it will be bonded.

by the way this building is just a small type trailer that is just seperately sitting in front of the other building. This has got be bonded in my opinion

The trailer frame will end up bonded to the building via the EGC in the feeder.

 

[domnic]

480/277 3 wire

480/277 3 wire

I thought if you had neutral at the transformer you must bring it in the building with the other wires.

 

[Smart $]

I thought if you had neutral at the transformer you must bring it in the building with the other wires.

Service xfmr to service disconnect. Not required thereafter, AFAIK.