OR Gates

OR gates allow you to represent a scenario in which the output event occurs if at least one of the input events occurs. In system reliability, this implies that if any component fails (input event), the system will fail (output event). In a reliability block diagram, this is equivalent to a series configuration.

The next two figures show both the fault tree diagram and reliability block diagram representation of a system with three components, A, B and C, in which the system fails if A, B or C fails. In a fault tree, this is modeled using the OR gate.

In an RBD, it is a series configuration.

To configure an OR gate, only the common block properties are available. No further configuration of the gate is necessary.