DC components in a PV system include modules, connectors, fuses, cabling, disconnects, combiner boxes, etc.  Failures and/or degradation in these components can result in declines in performance.  Depending on the type and location of failure or degradation the effects will differ in complex ways.  An example of a simple component failure is a blown fuse, broken wire or a connector which has failed causing an open circuit. Failures in modules are somewhat more complex. In the case of a module with three bypass diodes, open circuit failure of a cell or short-circuit failure of a bypass diode will reduce module output by one third.