Details
The assignments of the reference polarity for voltage and the reference direction for current are entirely arbitrary. However, once references are assigned, all subsequent equations must agree with the chosen references. The most widely used sign convention applied to these references is called the passive sign convention. The passive sign convention can be stated as follows:
Whenever the reference direction for the current in an element is in the direction of the reference voltage drop across the element (as in the figure here), use a positive sign in any expression that relates the voltage to the current. Otherwise, use a negative sign.
This sign convention is commonly used. The selection of polarity references along with the adoption of the passive sign convention is not a function of the basic elements nor the type of interconnections made with the basic element.