This theorem applies to networks containing linear bilateral elements and a single voltage source or a single current source. This theorem may be stated as follows:
If a voltage source in branch A of a network causes a current of 1 branch B, then shifting the voltage source (but not its impedance) of branch B will cause the same current I in branch A.
It may be noted that currents in other branches will generally not remain the same. A simple way of stating the above theorem is that if an ideal voltage source and an ideal ammeter are inter-changed, the ammeter reading would remain the same. The ratio of the input voltage in branch A to the output current in branch B is called the transfer impedance.
Similarly, if a current source between nodes 1 and 2 causes a potential difference of V between nodes 3 and 4, shifting the current source (but not its admittance) to nodes 3 and 4 causes the same voltage V between nodes 1 and 2.
In other words, the interchange of an ideal current source and an ideal voltmeter in any linear bilateral network does not change the voltmeter reading.
However, the voltages between other nodes would generally not remain the same. The ratio of the input current between one set of nodes to output voltage between another set of nodes is called the transfer admittance.