This circuit represents a typical North American residential service. The two transformers shown represent a single transformer with a single primary winding and a center-tapped secondary winding. The two 100 ohm resistors represent typical 120V loads such as a lamp or TV. The 200 ohm resistor represents a 240V load such as an electric dryer or oven. Try changing the value of one of the 120V loads. This causes the two "legs" to become unbalanced, which in turn causes a current to flow in the neutral line, represented by the Amperemeter. (NOTE: In reality, 240V or 120V are RMS values, which means the peak voltages are higher than shown here. RMS values are used for easier comprehension.)
