Question about the neutral wire in an electrical system

[pkelectrical]

If a phase touches another phase in a 3 phase AC supply it goes bang due to them being 120 degrees apart and therefore being at different voltages when they touch (this I understand), so WHY after passing through an electrical component, can all three phases be joined onto a 0 potential wire (the neutral)? Surely they are still out of phase and should still go bang?

1. What makes them be the same phase?
2. Why by going through electrical resistance it makes the voltage "OK" to go into zero potential wire? Ex. 120 line and a load (bulb)
3. How can in wye configuration the end of winding of each phase be joined together and not go bang?

I cant understand this, and I was not able to find an answer doing research. I would appreciate if someone could give me an answer to my questions.

Thank you in advance

 

[K8MHZ]

First you must realize that things 'go bang' because of voltage, not phases. DC goes bang, too.

1. 'Same phase' means the top of the voltage wave and the 0 crossing line happen at the same time. 120/240 residential is single, split phase. That means the 240 and 120 are in the same phase, coming from the same transformer created from the way the coil is tapped. You could also have 60/120/240 single phase by adding even more taps. Remember, voltage and phase are different critters. You can make all the taps and different voltages you want from one coil of a transformer and still have single phase, same phase for all voltages.

2. I don't understand what you mean by 'makes voltage OK'.

3. A wye can be joined without issue just like you could take 3 car batteries and tie all the negative terminals together and there would be no problem.

It sounds like you need some more training on basic electricity followed by basic AC theory. Without those basics, you may never understand electricity and how we make it useful. If doing your own research has not helped, you may want to consider some college courses on the subject.

 

[Smart $]

The 'bang' is from the sudden release of energy... i.e. voltage and current combined.

Consider a taser. Thousands of volts, little current, no 'bang'... but a similar 'sizzle'.

When you have a load (electrical resistance) in any circuit with voltage potential between points in the circuit, the load reduces the current enough to not go 'bang'.

 

[kwired]

First you must realize that things 'go bang' because of voltage, not phases. DC goes bang, too.

I will add a little to this.

The voltage is there party because of the phase angle. Change the angle somehow and the voltage will change.

It goes bang when two conductors with voltage between them are connected together because there is no resistance/impedance to current flow between them. Add a "load" and you have a resistance or impedance which limits how much current will flow.

Now there is resistance and impedance in conductors and the supply source, but for basic electricity 101 and getting a good understanding of things before going more complex, we assume conductors have no resistance and sources have infinite output ability for the simpler circuit calculations.

 

[Hameedulla-Ekhlas]

If a phase touches another phase in a 3 phase AC supply it goes bang due to them being 120 degrees apart and therefore being at different voltages when they touch (this I understand), so WHY after passing through an electrical component, can all three phases be joined onto a 0 potential wire (the neutral)? Surely they are still out of phase and should still go bang?

1. What makes them be the same phase?
2. Why by going through electrical resistance it makes the voltage "OK" to go into zero potential wire? Ex. 120 line and a load (bulb)
3. How can in wye configuration the end of winding of each phase be joined together and not go bang?

I cant understand this, and I was not able to find an answer doing research. I would appreciate if someone could give me an answer to my questions.

Thank you in advance

In an electrical system without a neutral, the voltage used will be divided across the midpoint of the circuit. if 120 volt line is directly connected to neutral, it could go "bang bang" but if it is connected 120 Volt line to a load and the other side of the load to the neutral, I think it could be ok.

 

[kwired]

In an electrical system without a neutral, the voltage used will be divided across the midpoint of the circuit. if 120 volt line is directly connected to neutral, it could go "bang bang" but if it is connected 120 Volt line to a load and the other side of the load to the neutral, I think it could be ok.

correct, that load limits the current that flows, directly connecting the 120 volt line to the neutral has very little resistance and therefore the only limiting factor is the impedance of the source, which in most cases is not much limitation either.

 

[pkelectrical]

First you must realize that things 'go bang' because of voltage, not phases. DC goes bang, too.

1. 'Same phase' means the top of the voltage wave and the 0 crossing line happen at the same time. 120/240 residential is single, split phase. That means the 240 and 120 are in the same phase, coming from the same transformer created from the way the coil is tapped. You could also have 60/120/240 single phase by adding even more taps. Remember, voltage and phase are different critters. You can make all the taps and different voltages you want from one coil of a transformer and still have single phase, same phase for all voltages.

2. I don't understand what you mean by 'makes voltage OK'.

3. A wye can be joined without issue just like you could take 3 car batteries and tie all the negative terminals together and there would be no problem.

It sounds like you need some more training on basic electricity followed by basic AC theory. Without those basics, you may never understand electricity and how we make it useful. If doing your own research has not helped, you may want to consider some college courses on the subject.

1. I understand this. The primary steps down voltage to secondary and creates 240v. The coil is divided in half and that point is grounded and now we have a neutral with the same phase as the ground. the Line 1 is -60v and line 2 is +60v in relation to the neutral wire.
2. Meaning the voltage from black wire goes through the bulb and into the neutral wire and nothing happens, but when normally without the resistance I would take black (hot) and neutral wire together and there would be bang. Smart explained this but now I'm trying to comprehend it.

I read Mike holt theory course and got the book. I also took physics in college and learn about this but they dont go in detail how the transformer works. was just basic theory about voltage and batteries.
They told us that electrons are negative charge and as they move through the bulb they lose some of the negative charge and become less negative. This was confusing since how can something that is negative loose more charge and become less negative, but anyway...

3. so wye is 3 different windings or 1 winding that is just in star shape?

 

[GoldDigger]

3. Three windings. They may be on individual cores or wound on a special three branched core for three phase.
For 120/240 it can either be one winding with a tsp connected at the middle or two windings with the ends connected at the terminal. And since it is one phase you have one iron core.

 

[kwired]

If a phase touches another phase in a 3 phase AC supply it goes bang due to them being 120 degrees apart and therefore being at different voltages when they touch (this I understand), so WHY after passing through an electrical component, can all three phases be joined onto a 0 potential wire (the neutral)? Surely they are still out of phase and should still go bang?

1. What makes them be the same phase?
2. Why by going through electrical resistance it makes the voltage "OK" to go into zero potential wire? Ex. 120 line and a load (bulb)
3. How can in wye configuration the end of winding of each phase be joined together and not go bang?

I cant understand this, and I was not able to find an answer doing research. I would appreciate if someone could give me an answer to my questions.

Thank you in advance

Question 1. the three inner ends of the wye connected windings have no complete circuit between one another (this is for a transformer or generator with no load yet connected). By connecting them together you do partially complete the circuit between the three points of the "star", and by adding "loads" you do finish completing circuit(s). Complete a circuit with a very low to near zero resistance and you get high current and a bang.

Queston 2. the neutral is not zero potential it is 120 volts from each phase (of a 120/208 system). If the neutral is grounded, and it almost always is in an NEC application, then the neutral is zero potential to ground, but only because ground is a fourth point that otherwise has no potential to the system that has been connected to it. Though it usually wouldn't be NEC compliant, from a physics perspective you could ground any of the other "phases" instead of the neutral, and that would leave you with 120 volts from neutral to that phase (as well as ground), and 208 volts from each of the other two phases to the grounded phase (as well as ground).

I think the answer to question 3 is kind of covered in the other 2 answers - they have no potential between them and no complete circuit path before they are connected and a load is added. Energize the transformer without those inner ends connected and there may be voltages between them, but they will not be stable, consistent, or predictable, and will disappear with even a pretty high resistance or impedance being connected between them as there is no complete circuit before they are connected, they would only have stable 120 volts to each opposing end of same coil.

 

[Smart $]

1. I understand this. The primary steps down voltage to secondary and creates 240v. The coil is divided in half and that point is grounded and now we have a neutral with the same phase as the ground. the Line 1 is -60v and line 2 is +60v in relation to the neutral wire.
2. Meaning the voltage from black wire goes through the bulb and into the neutral wire and nothing happens, but when normally without the resistance I would take black (hot) and neutral wire together and there would be bang. Smart explained this but now I'm trying to comprehend it.

I read Mike holt theory course and got the book. I also took physics in college and learn about this but they dont go in detail how the transformer works. was just basic theory about voltage and batteries.
They told us that electrons are negative charge and as they move through the bulb they lose some of the negative charge and become less negative. This was confusing since how can something that is negative loose more charge and become less negative, but anyway...

3. so wye is 3 different windings or 1 winding that is just in star shape?

1. Ground has no phase. Neutral has no phase. When bonded together, neutral is considered to be more stable with respect to non-circuit electrically conductive parts. On a 240VAC secondary with center tap (neutral), the magnitude of each end connection (line) varies with respect to neutral between +167V and -167V, approximately. Each line is the exact opposite polarity of the other and the waveform is sinusoidal. The root mean square of this voltage waveform is 120V_AC-RMS, which is used as an equivalent to 120V_DC in steady-state calculations.

2. Something does happen with the bulb. It's filament glows, converting electrical energy to other forms of energy: heat and light. Because of its resistance when glowing, current is substantially reduced compared to it not being in the circuit. The voltage drop across the bulb is exactly the voltage applied across its terminals (120VAC in the simplified analysis of electricity in use). Note the current magnitude and phase is the same on both the black and white wire.


Electrons maintain their charge regardless of position in the circuit. The first thing you have to realize about voltage is it is a measure of difference in potential. The measurement requires two points (or nodes) and one is typically considered the reference (typically the black lead of a voltage meter). If the black lead is connected to the neutral terminal at the source, and the red lead is connected to the neutral terminal at the bulb, you will be measuring only the voltage drop across the wire conductor. While the current is the same throughout the entire circuit, this voltage drop value will be minute compared to the voltage drop value one measures across the bulb terminals.

3. A wye configuration is three windings with one end of each winding connected together. The reference to wye or star is ethereal, mostly for graphic depiction. The physical positioning of the windings with respect to each other is seldom, if ever, in a wye or star configuration.

 

[GoldDigger]

One more way to think about the whole initial question it to realize that if you use a separate neutral for each phase, each neutral wire will be at (or very close to) zero volts. Considered as a sine wave for phasing, the voltage will go from a maximum of zero to a minimum of zero, passing through zero on the way.
Thus the statement that the neutral does not have a phase value. It could have any phase and the measured voltage would still be zero.
Now if you take the three separate neutral conductors and bang them together, no current will flow since they are all at the same voltage.
Just as when you bang together two hot conductors from the same line no current will flow because the voltage difference is zero.

 

[jaggedben]

If a phase touches another phase in a 3 phase AC supply it goes bang due to them being 120 degrees apart and therefore being at different voltages when they touch (this I understand), so WHY after passing through an electrical component, can all three phases be joined onto a 0 potential wire (the neutral)? Surely they are still out of phase and should still go bang?

The part highlighted in red is key to understanding why things do not 'go bang'. Any combination of the phase conductors and neutral touched to each other without passing through an electrical load will go bang. Any combination of them passing through a load will deliver energy to the load and usually not go bang.

1. I understand this. The primary steps down voltage to secondary and creates 240v. The coil is divided in half and that point is grounded and now we have a neutral with the same phase as the ground. the Line 1 is -60v and line 2 is +60v in relation to the neutral wire.

The voltages from each line to neutral are 120V. These are RMS (root-mean-square) voltages, which you can think of as a complicated way of averaging positive and negative voltages. Because it is alternating current the voltage changes polarity at a set frequency. Normally the cycle is 60 times a second in the United States, which means it changes polarity 120 times a second because one cycle goes through both directions. The highest voltage in the cycle is higher than 120 and the lowest voltage is 0.

You are correct that at the instant in a cycle when the voltage is -60V from line 1 to neutral, it will be +60V from line 2 to neutral, but this is just one instant in the constantly changing cycle.

Meaning the voltage from black wire goes through the bulb and into the neutral wire and nothing happens, but when normally without the resistance I would take black (hot) and neutral wire together and there would be bang.

Nothing happens? The bulb lights up, right? That is something happening. How much current passes through the bulb depends on the resistance of the bulb and the voltage supplied to it.

I think you're next step to understanding this is to look up Ohm's Law, Voltage = Current * Resistance or V=IR.

 

[pkelectrical]

Ok I understand this better one. I will meditate on this for some time so it sinks into my head. Thank you all for reply.