This paper presents two newly developed probabilistic models to perform reliability and availability analysis of three unit redundant systems with human errors. Model 1 represents a 2–out–of–3 unit system whereas Model 2 is concerned with a three non–identical unit standby system. The supplementary variables method, the Markov approach and Laplace transforms are employed to perform analysis. For both models system reliability, steady–state availability, mean time to failure and variance of time to failure formulae are developed. A number of plots are presented to demonstrate the effect of human errors and hardware failures.