![]() This rule was introduced in June 2007 (DIN VDE 0100-410 Nr. In contrast, Germany requires the use of RCDs on all sockets up to 20A which are for general use. In Europe, the UK has only mandated the use of RCDs in new installations since July 2008. Rules and regulations differ widely from country to country. The GFCI manufacturers provide tags for the appropriate installation description. In some countries, two-wire (ungrounded) outlets may be replaced with three-wire GFCIs to protect against electrocution, and a grounding wire does not need to be supplied to that GFCI, but the outlet must be labeled as such. These high-current RCDs serve more as an additional fire-safety protection than as an effective protection against the risks of electrical shocks. RCDs with trip currents as high as 500 mA are sometimes deployed in environments (such as computing centers) where a lower threshold would carry an unacceptable risk of accidental trips. Residual current detection cannot provide protection for overload or short-circuit currents. Residual current detection is complementary to over-current detection. If these do not sum to zero, there is a leakage of current to somewhere else (to earth/ground, or to another circuit), and the device will open its contacts. ![]() This measures the difference between the current flowing out the live conductor and that returning through the neutral conductor. RCDs operate by measuring the current balance between two conductors using a differential current transformer. In Europe, the commonly used RCDs have trip currents of 10–300 mA. GFCI devices which protect equipment (not people) are allowed to trip as high as 30 mA of current. In the United States, the National Electrical Code requires GFCI devices intended to protect people to interrupt the circuit if the leakage current exceeds a range of 4–6 mA of current (the trip setting is typically 5 mA) within 25 ms. RCDs are intended to operate within 25-40 milliseconds, before electric shock can drive the heart into ventricular fibrillation, the most common cause of death through electric shock. RCDs are designed to prevent electrocution by detecting the leakage current, which can be far smaller (typically 5–30 milliamperes) than the currents needed to operate conventional circuit breakers or fuses (several amperes). They can be found in kitchens, bathrooms, and other places that can be wet. ![]() In Australia they are sometimes known as “safety switches” or simply “RCD” and in the United Kingdom they can be referred to as “trips” or “trip switches”. In the United States and Canada, a residual current device is also known as a ground fault circuit interrupter (GFCI), ground fault interrupter (GFI) or an appliance leakage current interrupter (ALCI). RCDs are designed to disconnect quickly enough to mitigate the harm caused by such shocks although they are not intended to provide protection against overload or short-circuit conditions. A lethal shock can result from these conditions. Such an imbalance is sometimes caused by current leakage through the body of a person who is grounded and accidentally touching the energized part of the circuit. A residual-current device (RCD), similar to a Residual Current Circuit Breaker (RCCB), is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor.
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