A fault model for programmable logic arrays (PLAs) is discussed. This model maps realistic failures on four classes of faults: multiple stuck-at faults, multiple bridging faults, multiple crosspoint faults, and faults due to breaks in lines. It is shown that multiple stuck-at faults are equivalent to multiple crosspoint faults, multiple bridging faults are sub-equivalent to multiple crosspoint faults, and the set of patterns detecting multiple crosspoint faults is a subset of the set of patterns detecting multiple bridging faults. Hence, the set of patterns detecting multiple crosspoint faults also detects all multiple stuck-at faults and multiple bridging faults. This reduces the fault model for PLAs to two classes: multiple missing/extra crosspoint faults and multiple breaks.>