120/208, 1Ph, 3 Wire

[mivey]

And, sorry, we don't have two phase over here that I know of.
Not being argumentative. Just trying to be straight with the facts. I'm sure you understand.

Did the UK never have 2-phase? It was pretty popular at one time over here. I forget how that came to be exactly but I would think y'all would have had a similar development.

 

[mivey]

I have a scenario where there is a existing transformer in the field (no data on the existing transformer) and an adjacent Eaton Panel. The nameplate on the panel reads 120/208, 1Ph, 3W. Correct me if I'm wrong but the only way to get this voltage is to pull one phase off of a 3 phase transformer? If that is the case isn't technically split phase? I'm adding some small loads out their and was hoping to add a 40 amp 2 pole breaker to the Eaton board.

The other solution is to contact the utility and get info on the existing transformer, but that usually takes weeks...

Sounds like 208 is available. You have two 120 volt busses so a 2-pole breaker will get the 208 you want.

 

[mivey]

The existing transformer has no name plate on it, just a serial number for the utility. What I think happened is that this transformer has been sitting out in the yard for some time (it looks old) and they recently built a access control gate close by. They installed a rack with a service disconnect, meter, and the eaton panel and tapped into the old transformer. Since the gate only has some cameras and a small motor, 3 phase power was not required so they only pulled 1 phase off of it. I'm adding some small loads close by so the plan is to put a 2 pole 40 amp breaker into this existing eaton panel to feed a small panel to power up some street lighting. I just want to confirm I'm not loosing it :roll:

And I misspoke this is not split phase, it appears to be line-line

You are not losing it. You should be able to get the 40A, 208V you need.

 

[mivey]

I'm not sure until the utility gets back to me. My guess is the 208V is line-line with Y connection on the secondary of the existing transformer. The only other way I know how to get 208 is if the existing transformer is a delta with high leg configuration, which I never seen used with this particular client.

The high leg system would not be labeled 120/208 so you must have a wye secondary. The high-leg system would be 240/120 if three phase or 120/240 if single-phase.

 

[mivey]

The nameplate on the panel reads 120/208, 1Ph, 3W. Correct me if I'm wrong but the only way to get this voltage is to pull one phase off of a 3 phase transformer?

It uses 2 phases when fed wye-wye using two transformers instead of three. When fed delta-wye it uses 3 phases but still only needs two transformers.

The 3W 120/208 is called a network system but is also commonly referred to as a single-phase system because it serves single-phase loads.

 

[Besoeker]

Did the UK never have 2-phase? It was pretty popular at one time over here. I forget how that came to be exactly but I would think y'all would have had a similar development.

I can't say it never had but not that I recall. But I'm only ten years old...............

 

[jumper]

I can't say it never had but not that I recall. But I'm only ten years old...............

Sure.....using the canine unit system for age, so that makes you about seventy.

 

[Besoeker]

Sure.....using the canine unit system for age, so that makes you about seventy.

Close............
And my ca nine unit just patted me gently on the knee. Food, out, or attention.
He got all three.

 

[gar]

Do you have a voltmeter? It will answer your question.

.

 

[electrofelon]

Obviously (for those of us in the states) 120/208 single phase is real common in apartment and multi tenant buildings. Once though I was doing a resi service on a resi street, just assumed it was split phase like I always do. Got a call later from the utility guy, said I needed to add a fifth jaw clip because it was 120/208. I looked later and they had "stolen" two phases off a three phase bank feeding some commercial stuff and run it down the alley to pick up half the block.

 

[kwired]

Obviously (for those of us in the states) 120/208 single phase is real common in apartment and multi tenant buildings. Once though I was doing a resi service on a resi street, just assumed it was split phase like I always do. Got a call later from the utility guy, said I needed to add a fifth jaw clip because it was 120/208. I looked later and they had "stolen" two phases off a three phase bank feeding some commercial stuff and run it down the alley to pick up half the block.

Was kind of my thinking of what OP possibly has, or an older install had been abandoned but they are still using original source.

The way it is marked one would first assume it is two phase conductors and one neutral conductor supplying it. Might want to get out a voltmeter and confirm before making any design decisions.

 

[Besoeker]

Was kind of my thinking of what OP possibly has, or an older install had been abandoned but they are still using original source.

The way it is marked one would first assume it is two phase conductors and one neutral conductor supplying it. Might want to get out a voltmeter and confirm before making any design decisions.

Yet it is labelled 1-ph.

 

[jumper]

Yet it is labelled 1-ph.

How many phase angles are between any two poles in a star/wye system at a single instant?

No neutral in my question nor do I ask for a total for the system.

I have A, B, and C poles/tranny legs, whatever.

How many phase angles can exist between A and B at only one given time?

 

[kwired]

Yet it is labelled 1-ph.

with "/" in the voltage rating. That is supposed to mean both voltages are available, and typical supply that can create such voltages is 208/120 Y system, "single phase" says not all three "phases" are present.

I think I mentioned earlier (might have been another thread) that you can still derive a three phase supply from this using all three supply conductors - commonly done though usually from higher primary voltages with open delta secondary systems.

 

[electrofelon]

Yet it is labelled 1-ph.

Two phase conductors is different than two phase. Here we call two phase conductors single phase.

 

[Besoeker]

How many phase angles can exist between A and B at only one given time?

Oh, my.........that's a really hard question............

One of course and if that's all you were using then you would rightly call it single phase.
But, look at the nameplate in the first post. It shows 120V as one of the supplies. So you now have AN and AB. Not the same phase angle.
That's what makes me wonder about it being called 1PH.

 

[Besoeker]

Two phase conductors is different than two phase. Here we call two phase conductors single phase.

As would we.
But to get the 120V you need the neutral as well as the two lines.

 

[jumper]

Oh, my.........that's a really hard question............

One of course and if that's all you were using then you would rightly call it single phase.

Okay, I rest my case your honor.

No further questions.

I gotta run 'fore anyone else shows up.

Exit stage left.

 

[electrofelon]

As would we.
But to get the 120V you need the neutral as well as the two lines.

Even with a neutral, we still call it single phase. I hear ya, maybe In a perfect world, it would be called two phase, but that term is already used for a different system.

 

[Besoeker]

Even with a neutral, we still call it single phase. I hear ya, maybe In a perfect world, it would be called two phase, but that term is already used for a different system.

Might have been better to have left 1PH off the label.