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A residual-current device (RCD), residual-current circuit breaker (RCCB) or ground fault circuit interrupter (GFCI) [a] is an electrical safety device, more specifically a form of Earth-leakage circuit breaker, that interrupts an electrical circuit when the current passing through line and neutral conductors of a circuit is not equal (the term residual relating to the imbalance), therefore ...
A ground conductor only carries significant current if there is a circuit fault that would otherwise energize exposed conductive parts and present a shock hazard. In that case, circuit protection devices may detect a fault to a grounded metal enclosure and automatically de-energize the circuit, or may provide a warning of a ground fault.
In transmission line faults, roughly 5% - 10% are asymmetric line-to-line faults. [2] line-to-ground fault - a short circuit between one line and ground, very often caused by physical contact, for example due to lightning or other storm damage. In transmission line faults, roughly 65% - 70% are asymmetric line-to-ground faults. [2]
If the fault is on an adjacent circuit to the customer, the customer may see several brief "dips" (sags) in voltage as the heavy fault current flows into the adjacent circuit and is interrupted one or more times. A typical manifestation would be the dip, or intermittent black-out, of domestic lighting during an electrical storm.
When current flows from a line conductor to an earth wire, as is the case when a line conductor makes contact with an earthed surface in a Class I appliance, an automatic disconnection of supply (ADS) device such as a circuit breaker or a residual-current device (RCD) will automatically open the circuit to clear the fault. [7]
On the other hand double switching is inherently less prone to wrong side failures; it helps overcome short-circuit faults that are hard to test for. Partial double switching might double switch the lever controls, and the track circuits between one signal and the next, while single switching the track circuits in the less critical overlap ...
A ground fault protection relay must trip the breaker to protect the circuit before overheating of the resistor occurs. High-resistance grounding (HRG) systems use an NGR to limit the fault current to 25 A or less. They have a continuous rating, and are designed to operate with a single-ground fault.
The ELCB detects fault currents between line and earth (ground) conductors within the portion of the installation it protects. If sufficient characteristics of a fault appear across the ELCB's sensing mechanism, then it will switch off the power , and remain off until manually reset.
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