Calculating Failure Rates of Series/Parallel Networks

Introduction Recently, the author attempted to calculate the failure rate (FR) of a series/parallel (active redundant, without repair) reliability network using the Reliability Toolkit: Commercial Practices Edition published by the System Reliability Center as a guide. The Toolkit’s approach for FR calculation for a single branch seemed to be very thorough. So the FR for each individual branch was calculated. Since several branches were in series, the FRs the branches were then added together. Closer examination revealed that this approach was an oversimplification and failed to account for all possible combinations (ways) that individual components could fail. A closer review of the Reliability Toolkit revealed it treats FR calculations of single branches with n components in parallel very thoroughly but lacks detail in describing a method for handling multiple branches in series