How is this a balanced circuit with no current in the common/neutral wire?

[foolios]

How is this a balanced circuit with no current in the common/neutral wire?

The book I am reading states:

If R1 and R2 were not in the circuit, there would be no current in the common wire and the load on each side of the common wire would be the same, or as we say, the load would be "balanced". The balanced load is the same as having the load in series across a voltage of 240 volts.

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I don't understand what the author is trying to explain. It would appear to me that 240v should be still going across that neutral even without R1 and R2. Why would there not be any current at all going across it without those two resistors?

If someone could elaborate this further, I would really appreciate it.

Thank you so much in advance.

 

[Andy™]

current will flow around the entire circuit. if its balanced, then it will take path of least resistance, which would be round the outside, skipping the middle wire.

whatever electrons flow back to transformer in centre wire from top half, also flow the opposite direction towards the bottom half. if they are equal (which they will be with a balanced load) they cancel each other out so no current flows

240V would still exist between top and bottom, and 120V accross either of the 2 remaining resistances

 

[foolios]

Bear with me. I am really confused. I can't follow your explanation. Does this circuit have two hot legs? I think this might be where I am confused. Are you saying that the bottom wire is a neutral as well as the middle wire? Because otherwise, wouldn't the 120v from each side buck if they didn't use the neutral but instead flowed around the entire circuit? Skipping the middle wire.

whatever electrons flow back to transformer in centre wire from top half, also flow the opposite direction towards the bottom half.

the last bit I don't understand from this sentence. I see that electrons will flow in the common to the trans from the top half. But the flow in the opposite direction towards the bottom? Does this mean that electron flow will now go from the common to the bottom half? How so?

 

[SLIPSHOD & SLAPDASH]

No, the top & bottom are hot, the middle is the neutral

 

[Andy™]

each wire is hot, and 180 degress apart (i.e if the electrons more left in top wire, they move right in bottom wire). this is why there is a difference of 120V to neutral (centre point) and 240V between each phase.

if loads of perfectly balanced, the same current will flow all the way round the outside of circuit, and not use the centre wire, since there is no current to flow that way.

Now, if R1 & R2 was connected, then there would be an imbalance, so current from R1 & R2 would flow to neutral, but current from R3 & R4 would still skip neutral and go round the outside.

 

[SLIPSHOD & SLAPDASH]

To clarify Andys point about 180 degrees, this is the AC sinewave, at one point of the wave one phase is high, 180 degrees round the other phase is high.

mmmm i dont think i am explaining it to well

EDIT would it not be 120 degrees as the supply would be generated in three, even if only 2 phases are used here.

 

[Mr Sworld]

This is the concept of balanced three phase as used on motors. In fact three phase motors have no neutral at all. As the phases are balanced.