The lumped capacitance model, which ignores the existence of wire resistance, has been traditionally used to estimate the charging and discharging power consumption of CMOS circuits. We show that this model is not correct by pointing out that MOSFETs consume only part of the energy supplied by the source. During this study, it was revealed that about 20% of the power is consumed in the wire resistance of the buffered global interconnect, when the interconnect is modeled with RC tree networks. The percentage goes up to 30 when RLC model is used indicating the importance of inductance in interconnect model for power estimation. For RLC networks, we propose a compact yet very accurate power estimation method based on a model reduction technique.