  We consider the identifiability problem for the parameters of series-parallel
LCR circuit networks. We prove that for networks with only two classes of
components (inductor-capacitor (LC), inductor-resistor (LR), and
capacitor-resistor (RC)), the parameters are identifiable if and only if the
number of non-monic coefficients of the constitutive equations equals the
number of parameters. The notion of the "type" of the constitutive equations
plays a key role in the identifiability of LC, LR, and RC networks. We also
investigate the general series-parallel LCR circuits (with all three classes of
components), and classify the types of constitutive equations that can arise,
showing that there are 22 different types. However, we produce an example that
shows that the basic notion of type that works to classify identifiability of
two class networks is not sufficient to classify the identifiability of general
series-parallel LCR circuits.
