Single Ph. 208 /120 Transformer One-Line diagram--stuck on details

[hillbilly1]

Thank you INFINITY. I don't know transformers that well.
What am I missing?

1. Please remember I am stuck with 2 Hots and 1 Neutral conductor because its a direct bury under a busy area.
2. The Neutral is coming from the Neutral bus that is bonded to the Ground bus at the Panel.
3. I tied the Neutral to the Ground at the Counterpoise at the Site. (red circle)
4. What am I missing?
Thanks for your help View attachment 2557349

So the “neutral” originates at the service equipment? If so, and no other loads are on it, just change the tape color to green, and your done, no need to pull another wire just for the transformer.

 

[winnie]

I do not believe you are missing anything.

To supply the transformer you need 2 'hots' from your supply to provide 208V to the transformer.

You also need to protect this circuit with an EGC.

You do _not_ need a supply neutral. You need to repurpose your 'N' wire as an EGC.

Confirm that the supply neutral is in fact connected to the supply ground bus, which _may_ be the neutral bus only at the service equipment. If your supply is a 'sub-panel' then ground and neutral should be separate, and you may need to move the wire at the supply side. Additionally the _color_ of this wire might not be correct, and you may need to jump through some hoops there.

The transformer itself creates (or 'derives') a new source of current. You ground the neutral of the transformer secondary to create a proper grounded system.

-Jon

 

[oldsparky52]

That's neither near not there. 120-0-120 would be single phase. But once you introduce a 208V the angles are different. Thus are not single phase.
I know I have laboured this point and I appreciate your patience.

I think there might be a definition misunderstanding.

We all understand the 208V is from 2-phases of a 3-phase system, but because there is only one L-L connection, it's called single-phase.

 

[winnie]

But the 120-0-120 is a different phase to the 208. So, not single phase.

Again this is a purely terminology issue. With 120-0-120 and 208V L-L you have 3 different phase angles available to work with. But such is system is almost invariably used to supply single phase loads, and is called 'single phase'.

If you have the full 3 phase system (3 hots, 1 neutral, 3 separate L-N voltages and 3 separate L-L voltages) then you have _6_ different phase angles available. But we don't call this 6 phase, we call it 3 phase. And it is rare indeed to use all 6 available phase angles, though I believe that some members here use high pulse rectifier systems which use all of the available phase angles in phase shifting transformers.

-Jon

 

[Installer]

I do not believe you are missing anything.

To supply the transformer you need 2 'hots' from your supply to provide 208V to the transformer.

You also need to protect this circuit with an EGC.

You do _not_ need a supply neutral. You need to repurpose your 'N' wire as an EGC.

Confirm that the supply neutral is in fact connected to the supply ground bus, which _may_ be the neutral bus only at the service equipment. If your supply is a 'sub-panel' then ground and neutral should be separate, and you may need to move the wire at the supply side. Additionally the _color_ of this wire might not be correct, and you may need to jump through some hoops there.

The transformer itself creates (or 'derives') a new source of current. You ground the neutral of the transformer secondary to create a proper grounded system.

-Jon

 

[Installer]

winnie said:
I do not believe you are missing anything.

To supply the transformer you need 2 'hots' from your supply to provide 208V to the transformer.

You also need to protect this circuit with an EGC.

You do _not_ need a supply neutral. You need to repurpose your 'N' wire as an EGC.

Confirm that the supply neutral is in fact connected to the supply ground bus, which _may_ be the neutral bus only at the service equipment. If your supply is a 'sub-panel' then ground and neutral should be separate, and you may need to move the wire at the supply side. Additionally the _color_ of this wire might not be correct, and you may need to jump through some hoops there.

The transformer itself creates (or 'derives') a new source of current. You ground the neutral of the transformer secondary to create a proper grounded system.

-Jon

Hello Jon and thank you.
Please don't laugh. I can't open the Source Panel because its directly after the Utility Transformer and right now, there is no Main Disconnect Switch between the Utility and the Main Panel (Somebody made a mistake ). Even if I close the Main Breaker at the Source Panel, the incoming side of the Main breaker is Hot from the Transformer and City Rules prevent opening a Hot Panel. To open the Panel, I would have to call the Utility and shut down an entire City office building.
Can you enlighten me as to where the Neutral taps are on the Secondary?
Are you referring to the X3 and X2 tie?

 

[winnie]

To open the Panel, I would have to call the Utility and shut down an entire City office building.

[...]

Can you enlighten me as to where the Neutral taps are on the Secondary?
Are you referring to the X3 and X2 tie?

As you describe the source panel you can reliably surmise that it isn't a subpanel and that you can connect an EGC to the neutral bus.

You are correct, your derived secondary neutral is the X2 X3 tie, which your schematic correctly shows as a grounded neutral.

Jon

 

[Besoeker3]

Again this is a purely terminology issue. With 120-0-120 and 208V L-L you have 3 different phase angles available to work with. But such is system is almost invariably used to supply single phase loads, and is called 'single phase'.



-Jon

That's the crunch.

 

[jim dungar]

If you have the full 3 phase system (3 hots, 1 neutral, 3 separate L-N voltages and 3 separate L-L voltages) then you have _6_ different phase angles available. But we don't call this 6 phase, we call it 3 phase.

You are correct the total number of possible voltage angles is not the way we define polyphase circuits.

 

[Installer]

My thanks to everyone. Have a good day!

 

[GeorgeB]

That still baffles me - when you have 120/120/208V. It's different phases. Especially when it is explicitly states 208/120V 3-phase four wire.
And single phase........

It's just like your 415Y/240/50

 

[Besoeker3]

It's just like your 415Y/240/50

Except it isn't. There is no 120-0-120 for a start, We have 0-230V. And no 208V or similar.

 

[wwhitney]

Except it isn't. There is no 120-0-120 for a start, We have 0-230V. And no 208V or similar.

The 208Y/120 system is just half the voltage of your 415Y/240 (and a different frequency). So the 208V would correspond to the 415V L-L you have. Do you have any 2-wire 415V loads? Or are all loads either 2-wire 240V (L-N) or 3-wire 415V delta (L-L-L)?

Cheers, Wayne

 

[Besoeker3]

The 208Y/120 system is just half the voltage of your 415Y/240 (and a different frequency). So the 208V would correspond to the 415V L-L you have. Do you have any 2-wire 415V loads? Or are all loads either 2-wire 240V (L-N) or 3-wire 415V delta (L-L-L)?

Cheers, Wayne

But it isn't isn't half the voltage of the 415V - 240V is 1.732 tines 415V. Star versus delta if you like.

 

[petersonra]

But it isn't isn't half the voltage of the 415V - 240V is 1.732 tines 415V. Star versus delta if you like.

208 is 1.732 time 120.

208/120 is three phase wye, so it has a neutral, just like your 400/230 does.

Here it is not unheard of to use two of the 208 lines as 208 single phase (2 wire). It is single phase because there is just 120 degrees between any of the three hot lines, just like it is 120 degrees between any two of the hot lines in a European system. Any of the three lines to neutral gives you 120 V.

It is also not unusual here to run just two of the 208 V lines and a neutral. So you have 208 V line to line, and 120 V from either line to neutral.

 

[david luchini]

The 208Y/120 system is just half the voltage of your 415Y/240

But it isn't isn't half the voltage of the 415V - 240V.

I know math is hard, but 120 is definitely half of 240.

 

[Besoeker3]

I know math is hard, but 120 is definitely half of 240.

I think 120 is twice 240.
But 240Y is NOT 415V

 

[Besoeker3]

The 208Y/120 system is just half the voltage of your 415Y/240 (and a different frequency). So the 208V would correspond to the 415V L-L you have. Do you have any 2-wire 415V loads? Or are all loads either 2-wire 240V (L-N) or 3-wire 415V delta (L-L-L)?

Cheers, Wayne

We don'r use 208V.

 

[david luchini]

I think 120 is twice 240.

I think 480 is twice 240. Again, math is hard.

 

[wwhitney]

But it isn't isn't half the voltage of the 415V - 240V is 1.732 tines 415V. Star versus delta if you like.

Certainly within each wye system, the L-L voltage is 1.732 times the L-N voltage. That's expressed in the nomenclature 415Y/240, that means a wye system with 415V L-L and 240V L-N.

So the UK has 415Y/240 (as I understand it, or 400Y/230 nominal for EU harmonization). The US has 208Y/120. The US system is half the voltage of the UK system, for L-L or L-N or any corresponding measurement.

Now how about my question, is it common to have 2-wire 415V (or 400V) loads in UK/Europe? Here it is not uncommon to have loads that are designed for 2-wire 208V, which can be run L-L on a 208Y/120 system.

Cheers, Wayne