3 phase Voltage

[td1236]

3 phase voltage is 240 between all phases, A phase to ground is 120, B phase to ground is 208 C phase to ground 120.

Why would B phase to ground be 208?

 

[ptonsparky]

It’s a high leg delta configuration. Either open or closed delta.

 

[infinity]

As Tom stated it's a 3 phase, 4-wire Delta system. One of the coils has a center tap to provide the 120 volts but has a higher voltage to neutral typically from the B phase.

 

[LarryFine]

 

[qcroanoke]

3 phase voltage is 240 between all phases, A phase to ground is 120, B phase to ground is 208 C phase to ground 120.

Why would B phase to ground be 208?

What everyone else said plus it should have been identified by being orange.

 

[GoldDigger]

As Tom stated it's a 3 phase, 4-wire Delta system. One of the coils has a center tap to provide the 120 volts but has a higher voltage to neutral typically from the B phase.

Which, by the original definition makes it not a true "neutral" conductor (same voltage to all ungrounded conductors), but the Code decided to call it one anyway in this context.

 

[LarryFine]

Which, by the original definition makes it not a true "neutral" conductor (same voltage to all ungrounded conductors), but the Code decided to call it one anyway in this context.

Considering that the high-leg open delta started as a modification to existing 1ph services, I think it still fits.

I can't think of a better term for it, especially to the A_C winding. It's definitely still the grounded conductor.

 

[GoldDigger]

Considering that the high-leg open delta started as a modification to existing 1ph services, I think it still fits.

I can't think of a better term for it. It's definitely still the grounded conductor.

Whereas, I would say that the white wire started out as a neutral, but stopped being one when the third phase conductor was added.
I would just call it the grounded conductor. Among other things, I think the white wire needs to be counted as a CCC in a full boat if the high leg is used for single phase loads.

 

[ptonsparky]

Which, by the original definition makes it not a true "neutral" conductor (same voltage to all ungrounded conductors), but the Code decided to call it one anyway in this context.

I preferred when we called it a grounded conductor myself.

 

[LarryFine]

Among other things, I think the white wire needs to be counted as a CCC in a full boat if the high leg is used for single phase loads.

Which I believe we generally agree shouldn't be done.

 

[LarryFine]

I preferred when we called it a grounded conductor myself.

I remember it being called "the identified conductor."

 

[ptonsparky]

I remember it being called "the identified conductor."

Rings a bell.

 

[infinity]

I like the "new" version where we call it a neutral. It's a white conductor that most call a neutral anyway. I never really saw the need to have a distinction between a neutral and a grounded conductor with a 4-wire Delta system.

 

[wwhitney]

It's a single phase neutral and also a grounded conductor. It's not a 3 phase neutral.

Cheers, Wayne

 

[d0nut]

3 phase voltage is 240 between all phases, A phase to ground is 120, B phase to ground is 208 C phase to ground 120.

Why would B phase to ground be 208?

Trigonometry.
Just like was discussed in this thread: https://forums.mikeholt.com/threads/three-phase-ampacity-calculations.2577416/
Refer to the image in post #4 of this thread for the visual representation.

You have a 30-60-90 triangle, know the short leg (120V) and the hypotenuse (240V), and are looking for the long leg.
cos(30)=x/240V
Sqrt(3)/2=x/240V
x=120V*Sqrt(3)
x=208V

 

[Frank DuVal]

It is the grounded conductor.
It's a neutral.
It is white.
Yes, if you use the high leg conductor and neutral you get 208 volts (190 to us old guys!).
That's why electricians should carry voltmeters!

Wayne is right!

 

[kwired]

It's a single phase neutral and also a grounded conductor. It's not a 3 phase neutral.

Cheers, Wayne

The "three phase neutral" is someplace inside the delta but has no real connection we can utilize.

 

[Jraef]

… but has no real connection we can utilize

And yet, this question (using the 208V for something) arises here (and elsewhere) surprisingly often. I think if it kind of like having a button on the wall with a sign that says “DON’T PUSH THIS BUTTON!”, there will always be someone who has to push it.

 

[kwired]

And yet, this question (using the 208V for something) arises here (and elsewhere) surprisingly often. I think if it kind of like having a button on the wall with a sign that says “DON’T PUSH THIS BUTTON!”, there will always be someone who has to push it.

What I was getting at was the true neutral of the delta itself is a point in the center of the delta that has no possible way to connect to without some sort of wye connected circuit between the three corners of the delta.