Neutral for each Phase

Status
Not open for further replies.
j rae said:
Is it required to run a neutral for each ckt ??
Click to expand...

ptonsparky said:
No. You may use a MWBC, if you use circuit breakers with handle ties or a multipole CB. 210.4. Specs or local rules may have precedence.
Click to expand...

Question is somewhat vague. Yes, for every 110v circuit you must run a neutral, however, as ptonsparky pointed out, it does not need to be a dedicated neutral.
 
Interesting. I once supplied fairly large 3ph delta transformer that had a center tap on each winding. What the engineer wanted the ability to supply (3) Separate 120/240v 1ph3w loads. As such there was a neutral per phase. It worked out fantastic and a second one was ordered a year later with yet another order pending. The transformer was built such that each of the corners of the delta were not connected to on another forming essentially (3) single phase transformers that way we could tie the (3) neutrals together.
But this was my experience with one neutral per phase.
 
templdl said:
Interesting. I once supplied fairly large 3ph delta transformer that had a center tap on each winding. What the engineer wanted the ability to supply (3) Separate 120/240v 1ph3w loads. As such there was a neutral per phase. It worked out fantastic and a second one was ordered a year later with yet another order pending. The transformer was built such that each of the corners of the delta were not connected to on another forming essentially (3) single phase transformers that way we could tie the (3) neutrals together.
But this was my experience with one neutral per phase.
Click to expand...

If you really had a delta configuration with a center tap on each of the line-to-line windings, then you could not connect the three neutrals together without setting up really strange line-to-line voltages which would make it impossible to drive an actual three phase load. Instead of L1, L2 and L3, you would have L1a, L1b, L2a, L2b, L3a and L3b, all at 120 volts to the neutral, but with 6 different phase vector directions. Great for a 12 pulse rectifier, but not much else.
By choosing connections properly, you could sort two 208/120 three-phase system out of them, with a 60 degree phase offset between them. Labeling would be a serious issue!
 
GoldDigger said:
If you really had a delta configuration with a center tap on each of the line-to-line windings, then you could not connect the three neutrals together without setting up really strange line-to-line voltages which would make it impossible to drive an actual three phase load. Instead of L1, L2 and L3, you would have L1a, L1b, L2a, L2b, L3a and L3b, all at 120 volts to the neutral, but with 6 different phase vector directions. Great for a 12 pulse rectifier, but not much else.
By choosing connections properly, you could sort two 208/120 three-phase system out of them, with a 60 degree phase offset between them. Labeling would be a serious issue!
Click to expand...

Yes, you are correct if you connected the corners of an actual delta connected secondary of a transformer and center tapped each winding of course the center taps could not be connected. If you were to do so very bad this very bad things will happen like letting the smoke out and sparks may even fly. But, in fact they were not.* The corners of the delta configured secondary were not connected together and that's what made it unique. I had (3) individual (individual is the key word here) 240v single phase windings 120deg apart each winding of which was center tapped for a neutral point and all attached together.
It consisted of one 18 wheeler with* 3ph diesel driven generator providing power to a second 18 wheeler containing the power distribution with (2) transformers one of which was this custom (3) transformer with the unique secondary. When I got the call from the engineering firm it took me a day or two two understand the concept. Once I did they were related because they found no other manufacturer had. They need a large amount of* 1ph kva which which they could only a achieve with* 3ph* generator supplying power to a d-d transformed with the secondary configured into (3) individual 1ph 240v windings. I've never heard of this before and I think it is a brilliant idea for this application.
It works awesome. The customer wanted everything top notch specifying copper windings. This was great until they found that with (2) massive transformers in the trailer it was overweight for the a axle design and the axle had to be re-configured. With the second order I recommended aluminum windings, an aluminum enclosure as well as replacing as much structural steel where In was able to reduce the weight significantly.
After I understood their power design it made complete sense. I would like to post some pictures of these massive trailers but my practice is to keep my customers confidential. You would quickly recognize the beautiful white trailers while the blue logo on the side.

Custom transformers? I took an order and had a 3ph-2ph core and coil only transformer built that was much taller than you and I are that shipped to a company in Mexico, not the baby sizes that are found in eastern Pennsylvania. I also have a 1500kva core and coil that I shipped to Australia that was specially to be installed in a TENV nitrogen charged enclosure for use in an underground mine as I recall.
I found that custom transformer applications with the support of a great engineering staff as well as manufacturing capabilities were both challenging and fun. I shipped (3) huge air core current limiting reactors each reactor of a 3ph bank with at least a10'x 10' x 10' enclosure which required special DOT permits to ship.
 
templdl said:
The corners of the delta configured secondary were not connected together and that's what made it unique.
...and I think it is a brilliant idea for this application.
Click to expand...

Somehow I have a problem in my mind calling it a delta secondary when the corners of the triangle are not connected. :)
It may have been wound physically as you would have for a delta when building the transformer, but that alone does not make it a delta to me.
If it catches on, we may need to come up with a new term for it. I nominate asterisk (*) for that purpose. :)
 
Neutral for each phase?

Neutral for each phase?

It would no longer be a neutral, they would be grounded conductors since they do not share currents from each phase:p Every neutral is a grounded conductor, but not every grounded conductor is a neutral:lol:
 
Canton said:
It would no longer be a neutral, they would be grounded conductors since they do not share currents from each phase:p Every neutral is a grounded conductor, but not every grounded conductor is a neutral:lol:
Click to expand...
Wrong on two out of three counts.
1. Since the amplitude of the voltage from that particular line to each of the other six wires is identical, it is by definition a neutral wire. Whether you ground it or not, and regardless of what the exact phase relationships are. The fact that the phase vectors are in fact uniformly distributed around it in a circle would also allow it to be called the neutral wire of a six phase system.

2. There are a small number of system configurations under the NEC in which you are not required to ground the neutral conductor if there is one.

3. But it is definitely true that not every grounded conductor is a neutral.
 
Maybe I did not read carefully enough but sounds to me like three individual single phase separately derived systems, that happen to be balanced across the input. The only way you could possibly connect a three phase load to them is to connect the "corners" together then you effectively make it into a single three phase system instead of three single phase systems, but you can't keep all three mid point bonds either once you connect the corners.
 
kwired said:
Maybe I did not read carefully enough but sounds to me like three individual single phase separately derived systems, that happen to be balanced across the input. The only way you could possibly connect a three phase load to them is to connect the "corners" together then you effectively make it into a single three phase system instead of three single phase systems, but you can't keep all three mid point bonds either once you connect the corners.
Click to expand...
I think that a careful reading will sort it out to be entirely 120 volt or 240 volt loads, each connected to one of three "independent" 120/240 systems that happen to be powered from a three-phase source through a three-phase unit transformer instead of three separate pots. And you can bond all of the midpoints as long as you do not interconnect any of the corners. You can look at it as two 208Y/120 systems which are 60 degrees out of phase with each other and have a common neutral point. (180 - 120 = 60)
So if you wanted to power three phase loads from it (which the OP did not) they would have to be 208/120 three phase loads, and you would not need to bond any of the corners of your wye configuration system.
When only single phase loads exist, the single phase versus three phase nature of a system is primarily of interest to the poor electrician who is trying to make sense of the wiring by measuring voltages only.
Oh, just to complete the confusion, the line-to-line voltage between any two lines which are adjacent around the phase circle will also be 120 volts.
Which means, among other things, that you can also look at the result as six separate corner-grounded 120 volt deltas of differing phases which have had some of their corners selectively connected. My head hurts, but the drawing still looks right.
 
kwired said:
Maybe I did not read carefully enough but sounds to me like three individual single phase separately derived systems, that happen to be balanced across the input. The only way you could possibly connect a three phase load to them is to connect the "corners" together then you effectively make it into a single three phase system instead of three single phase systems, but you can't keep all three mid point bonds either once you connect the corners.
Click to expand...

Bingo. This is used on a portable system where the diesel 3ph generator is located one enclosed trailer with dual tandems and the transformers and switch gear are located in a second similar trailer.
Yes, what I tried to describe, maybe somewhat poorly, is that they wanted (3)separately derived 120/240 1ph3w systems where there neutral points were tied together.
When my customer approached me with this concept it took we a while to understand what he wanted. He did comment that of all the transformer manufactures that he contacted I was the only one who understood what he wanted. He gave me the ball and I ran with it. I'd love to share the pictures that I have of it. They are awesome.
 
GoldDigger said:
I think that a careful reading will sort it out to be entirely 120 volt or 240 volt loads, each connected to one of three "independent" 120/240 systems that happen to be powered from a three-phase source through a three-phase unit transformer instead of three separate pots. And you can bond all of the midpoints as long as you do not interconnect any of the corners. You can look at it as two 208Y/120 systems which are 60 degrees out of phase with each other and have a common neutral point. (180 - 120 = 60)
So if you wanted to power three phase loads from it (which the OP did not) they would have to be 208/120 three phase loads, and you would not need to bond any of the corners of your wye configuration system.
When only single phase loads exist, the single phase versus three phase nature of a system is primarily of interest to the poor electrician who is trying to make sense of the wiring by measuring voltages only.
Oh, just to complete the confusion, the line-to-line voltage between any two lines which are adjacent around the phase circle will also be 120 volts.
Which means, among other things, that you can also look at the result as six separate corner-grounded 120 volt deltas of differing phases which have had some of their corners selectively connected. My head hurts, but the drawing still looks right.
Click to expand...
I was with you until you started talking about wye systems. There are no "corners" on a wye system and that had me even further lost in whatever you were trying to say.
 
kwired said:
I was with you until you started talking about wye systems. There are no "corners" on a wye system and that had me even further lost in whatever you were trying to say.
Click to expand...
OK, I would call the non-common ends of the wye legs corners just for the sake of lazy use of language. But if you make the necessary substitution based on the fact that one can consider the ends of the wyes as corners of an inscribed hexagon inside the phase circle, it should become perfectly clear or remain totally obscure. ;)
Corners of the triangles formed when you represent it schematically, not corners of a connected wire pattern.
Take a conventional drawing of wye secondary. Color it blue. Take another wye, colored red and rotate it 60 degrees about the neutral, either CW or CCW, and then superimpose it on the first one. As you go around the circle on which the outer ends of the wyes lie, you will encounter first a red point, then a blue point, alternating until you reach your starting point.
The adjacent red-to-blue voltage will be 120 if each circuit is 120Y/208. Any same-color to same-color voltage (except for the neutral) will be 208. Other voltages which link red to blue may be completely weird, with a maximum of 240 when you go across on a diameter of the circle. That gives you two wyes.
If instead you color the lines black red and blue, corresponding to the windings they come from, it looks like three crossed 120/240 systems.

Which is a more useful way to look at it depends on what you are trying to calculate or understand.

(Light: Wave or Particle?)
 
GoldDigger said:
OK, I would call the non-common ends of the wye legs corners just for the sake of lazy use of language. But if you make the necessary substitution based on the fact that one can consider the ends of the wyes as corners of an inscribed hexagon inside the phase circle, it should become perfectly clear or remain totally obscure. ;)
Corners of the triangles formed when you represent it schematically, not corners of a connected wire pattern.
Take a conventional drawing of wye secondary. Color it blue. Take another wye, colored red and rotate it 60 degrees about the neutral, either CW or CCW, and then superimpose it on the first one. As you go around the circle on which the outer ends of the wyes lie, you will encounter first a red point, then a blue point, alternating until you reach your starting point.
The adjacent red-to-blue voltage will be 120 if each circuit is 120Y/208. Any same-color to same-color voltage (except for the neutral) will be 208. Other voltages which link red to blue may be completely weird, with a maximum of 240 when you go across on a diameter of the circle. That gives you two wyes.
If instead you color the lines black red and blue, corresponding to the windings they come from, it looks like three crossed 120/240 systems.

Which is a more useful way to look at it depends on what you are trying to calculate or understand.

(Light: Wave or Particle?)
Click to expand...
I understand that now that you described it a little better. But sorry I don't see how it relates to the delta system discussed in this thread.

One could also have a delta system or multiple single phase systems wired around your multiple wye systems and have one common point of every one of them bonded together. In fact we already do bond them together (most of the time), but to overlap wye systems by 60 degrees they would have to come from two separate sets of windings placed 60 degrees apart on the same source, some other intentional phase shift needs introduced, or we make the "phases" with solid state devices, or two steady sources that are operating 60 degrees apart.
 
kwired said:
I understand that now that you described it a little better. But sorry I don't see how it relates to the delta system discussed in this thread.

One could also have a delta system or multiple single phase systems wired around your multiple wye systems and have one common point of every one of them bonded together. In fact we already do bond them together (most of the time), but to overlap wye systems by 60 degrees they would have to come from two separate sets of windings placed 60 degrees apart on the same source, some other intentional phase shift needs introduced, or we make the "phases" with solid state devices, or two steady sources that are operating 60 degrees apart.
Click to expand...

What you are missing out on is the fact that each winding is center tapped, and so you have a 180 degree phase shift available. And (180 - 120) = 60.
That is why I can say that the system composed of one end of each center-tapped winding will be 180 degrees out of phase with the system composed of the other ends of each winding.
The result can also be looked at as two separate three phase sets of lines which are offset by 180 degrees. And that, just by relabeling the wires, becomes two sets offset by 60 degrees. Vector magic.
 
GoldDigger said:
What you are missing out on is the fact that each winding is center tapped, and so you have a 180 degree phase shift available. And (180 - 120) = 60.
That is why I can say that the system composed of one end of each center-tapped winding will be 180 degrees out of phase with the system composed of the other ends of each winding.
The result can also be looked at as two separate three phase sets of lines which are offset by 180 degrees. And that, just by relabeling the wires, becomes two sets offset by 60 degrees. Vector magic.
Click to expand...
I don't think I missed that. I do see that you have a source with some capabilities that could come in handy at times, but would cost a lot more than it is worth in most cases also.
 
Status
Not open for further replies.
Top