The Cauer Ladder Network (CLN) method proposed at the origin by Kameari et al. enabled to reduce a numerical model based on a 2D vector potential FE formulation of the magnetoquasistatic (MQS) problems. Since then, extensions have been proposed to other formulations in MQS and electroquasistatic (EQS) problems. The main advantage of this method is that the reduced problem relies on an equivalent electrical circuit. It means that once the reduced basis is built in an offline stage, the online stage consists in solving an electrical circuit. The field distributions in the FE space are then reconstructed from currents and voltages. Using the CLN method, the coupling of other circuits is totally natural, which is of great interest in many applications since the device, modelled by the FE method, is very often electrically connecting to other devices represented also by equivalent circuit. In this communication, we propose to show how the CLN method can be used to study MQS and EQS problems. In the MQS case, we show briefly how the CLN method enables to construct reduced models from Finite Element (FE) potential formulations (A-φ, T-Ω and A-T). These reduced models are based on equivalent electrical circuits associating resistances and inductances. The method is applied to construct a reduced model of a Printed Board Circuit which is coupled with models of power switches in order to study the behavior of a power converter. In the EQS case, the CLN method can also be used to derive, from a FE scalar potential formulation, an equivalent circuit associating resistances and capacitances. To illustrate the possibility offered by the CLN method, it is applied to study a resin-impregnated paper bushing (component of High voltage transformer) and the influence of default of insulation.