Most residual current devices are designed for 240V AC circuits, but some may be rated for 110V or 415V three-phase supplies. During the RCD selection procedure, this is one of the key specifications that you must check., then the circuit breaker can also guarantee protection through automatic disconnection. Therefore, an RCD exposed to such waveforms needs to be of a suitable type, otherwise a distorted waveform (or DC) could aff ect the time/current operation of an RCD and cause it to operate outside its correct operating characteristics – or, at worst, the RCD could fail to urrent. Residual Current Devices (RCDs) are safety switching devices. RCDs not. RCD stands for residual current device. In the US and Canada, you may encounter them referred to as ground fault circuit interrupters (GFCIs). When allowed, and particularly when ABB RCDs are employed, the installer may advantageously choose a less-than-B type RCD upstream, as per BB rec-ommendations and as described in chapter 4 electric power supply and on load characteristics.