Editing Residual-current device (section)

===Trip time===
Trip times are how quickly the device reacts to a fault. Devices must meet specific trip times when leakage current is sensed, with times ranging from tens to hundreds of milliseconds, as defined in national and international standards. The amount of time may vary depending upon the amount of current sensed, potentially having to react quicker to larger amounts, and to not react at all if the amount is sufficiently below the device rating.

In contrast to ''general'' types, ''S-type'' (aka ''time delayed'') RCDs include a time delay — a minimum amount of time during which the device will not react — and typically higher maximum reaction time limits. This time delay allows for ''discrimination'' (aka ''selectivity'') which is the principle that where two RCDs are installed in series, in the even of a fault it is desirable for the downstream device (which would typically cover a smaller portion of the installation) to trigger rather than the upstream in order to minimise how much of the electrical installation is disconnected. The upstream device should only trigger if the downstream device fails to react or if the fault is located between the two devices.

''Programmable'' devices may be available for industrial use that can be adjusted to a range of sensitivity values and possibly response times.