Neutral sharing

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Sanaka,

I think a better way to look at this is that each of the wires is a reference point rather than an actual voltage. The distance between any two reference points is our effective voltage. For consistancy we will refer to the neutral as our 0 volt reference point and leg A as our 120 volt potential, and leg B as our -120 volt potential. If you measure between Leg A and Netral, you will measure 120 volts, and if you measure between Neutral and Leg B, you will again get 120 volts, but if you measure between Leg A and Leg B, instead you will measure 240 volts.

Next, lets say you connect both sides of a 240 volt circuit to the same leg (ie Leg A), well now when we measure between Leg A and Leg A (2), we get a result of 0 volts. In the case of a Dryer, the controll circuits (which connect between Leg A and Neutral) will receive their expected voltage of 120v, where as the heating elements (which only connect to the two legs and not the neutral) will form a circuit between wires of equal potential (120v - 120v = 0v), which will not induce the flow of electrons (ie current).
 
jimwalker said:
Should you change the bulbs to say a 50 watt and a 100 watt ,the neutral now has some unbalanced current.And if you were to remove that neutral the voltage across the 50 watt would 160 volts and across the 100 you have 80 volts.
Click to expand...

Jim never did show his work --

Trotting out Ohm and his Law ...

E = I * R
P = E * I

Since we know E = 120 for the normal case of 120v 'legtricity, we can solve for R in the instances of 50 and 100 watt bulbs.

P = E * I
I = E / R
P = E ^ 2 / R
R = E ^ 2 / P

For a 50 watt bulb, R = 120 * 120 / 50, R = 288 Ohms. For a 100 watt bulb, R = 120 * 120 / 100, R = 144.

Now we put them in series for a total resistance of 288 + 144 = 432 Ohms and compute the current. I = E / R, I = 240 / 432, I = 0.556A.

Computing voltage drop is another trip back to Ohm. E = I * R. For the 50 watt bulb, E = 0.556 * 288, E = 160. For the 100 watt bulb, E = 0.556 * 144, E = 80.
 
Thanks

tbonse for that further clear elucidation. how this worls is really pretty simple, yet somehow slippery, and I need to refresh my brain on it periodically

And tallgirl for that math. Ohm rocks!

Peace,
Sanaka
 
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