Look at the first schematic diagram below.
Note: Load 1 and load 2 are identical. The loads are Balanced.
Note: The shared "neutral". 0 A (The shared neutral is not involved).
Load 1 and load 2 are in series with one another and are fed by 240V
Addition of neutral conductor allows loads to be individually driven.
Instead of a single 240 volt power supply, we use two 120 volt supplies (in phase with each other!) in series to produce 240 volts, then run a third wire to the connection point between the loads to handle the eventuality of one load opening. This is called a split-phase power system. Three smaller wires are still cheaper than the two wires needed with the simple parallel design, so we’re still ahead on efficiency. The astute observer will note that the neutral wire only has to carry the difference of current between the two loads back to the source. In the above case, with perfectly “balanced” loads consuming equal amounts of power, the neutral wire carries zero current.
Notice how the neutral wire is connected to earth ground at the power supply end. This is a common feature in power systems containing “neutral” wires, since grounding the neutral wire ensures the least possible voltage at any given time between any “hot” wire and earth ground.
An essential component to a split-phase power system is the dual AC voltage source. Fortunately, designing and building one is not difficult. Since most AC systems receive their power from a step-down transformer anyway (stepping voltage down from high distribution levels to a user-level voltage like 120 or 240), that transformer can be built with a center-tapped secondary winding: (Figure below)
American 120/240 Vac power is derived from a center tapped utility transformer.
https://www.ibiblio.org/kuphaldt/electricCircuits/AC/AC_10.html
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Note: See the two 120V rectangles?
Connect a 2A digital load across one and a 2A analog load across the other. 0 amps will return on the shared neutral. the two loads are in series and are fed by 240V
