Editing Residual-current device (section)

==Testing of correct operation==
[[File:Moeller Xpole PXF-40-4-003-A - case removed-2371.jpg|thumb|Test button (yellow), of a partially disassembled RCD]]
RCDs can and should be tested with a built-in test button to confirm basic functionality on a regular basis. If the switch mechanism is not operated for a long period then they can become liable to getting stuck. This is not generally a problem for an overcurrent circuit breaker because the force from the amount of current involved with those when they trip can be sufficient to break them free if stuck, however an RCD is designed to trip on a very small amount of current which can excerpt far too weak a force to break a stuck switch free, thus failing to operate the safety device. By operating the test button on a regular basis it can be seen whether or not a device is getting stuck. If so then manually operating the switch a few times may free it up temporarily and replacement can be considered. More thorough testing performed by a suitably competent person as part of a periodic test of an electrical installation might include checking what amount of current is required to make each device trip, and how quickly they trip, to check that they are performing within specification.