As the number and complexity of System Integrity Protection Schemes (SIPS) in operation increases very rapidly, it must be ensured that their performance meets the reliability requirements of electrical utilities, in terms of dependability and security. A procedure based on Markov Modeling and Fault Tree Analysis is proposed for assessing SIPS reliability. Many operators tend to have SIPS permanently in service; this reduces the probability the arming software or the human operator will fail to arm the SIPS. Whilst this can decrease the probability of dependability-based misoperation, it may increase the probability of security-based misoperation. Therefore, the impact of having SIPS always armed is examined and compared with the impact of arming the schemes only when required. In addition, two reliability indices are introduced for quantifying the level of SIPS reliability: Safety Integrity Level and Spurious Trip Level. The proposed method is illustrated using the South of Lugo "N-2" SIPS, which is part of the South California Edison grid.