Guys,
When the full 240V secondary winding is used to feed a 240V load the winding works like any other single phase transformer winding.
Things change when 120V loads are connected to L1, leg, and the neutral, and L2, leg, and the neutral. This is where the polarity of each side of the secondary split phase winding gets interesting.
If L1 to neutral and L2 to neutral loads are exactly the same amperage, zero amps will return on the neutral conductor to the transformer neutral center tap. Example 10 amp load connected to L1 and neutral and 10 amp load on L2 and neutral. Zero amps will return on the neutral conductor to the center tap neutral on the transformer. The two 120V loads will be in series with one another and fed by 240V. If a10A load is connected to L1 and neutral and 5A load connected to L2 and neutral, the unbalanced load of 5 amps will return on the neutral conductor.
On a single phase dual winding secondary it is important to observe the polarity of the windings when connecting them together.
How it works.
https://www.allaboutcircuits.com/textbook/alternating-current/chpt-10/single-phase-power-systems/
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