This Paper analyses several model-order reduction methods and then proposes an improved n model and a new delay calculation method to be used in analyzing RC-class interconnects, which does not involve moment calculation processes. The proposed delay calculation method has been derived by combining the unproved model, the concept of effective capacitance and Elmore delay. This method has an advantage in that it can be applied in the calculation of end-to-end delay as well as incremental delay.