This paper presents a new table based algorithm for overcurrent relay with inverse-time characteristic. The algorithm is based on loading the adequate time vector through which inverse-time characteristic is modeled. It uses samples of the current and calculates rms value. The rms current represents an input value for the index estimation what determines corresponding element from already loaded time vector. Since the calculations used in this algorithm are based on simple mathematical operations, short processing time is achieved. Performances of the algorithm are tested by several computer-generated signals. Furthermore, comparative analyses showed indisputably that suggested procedure possesses significant advantages compared to other solutions: simplicity, high speed of operation and accuracy.