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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]
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.
A residual-current device (RCD), residual-current circuit breaker (RCCB) or ground fault circuit interrupter (GFCI) [a] is an electrical safety device that interrupts an electrical circuit when the current passing through a conductor is not equal and opposite in both directions, therefore indicating leakage current to ground or current flowing to another powered conductor.
(The principle of double fault to danger requires either basic and additional insulation to fail or basic insulation and the connection to the protective earth to fail simultaneously before danger arises.) A typical example for a PELV circuit is a metal cased computer with a Class I power supply.
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]
If a second ground fault occurs, a ground fault protection relay must trip the breaker to protect the circuit. On an HRG system, a sensing resistor is used to continuously monitor system continuity. If an open-circuit is detected (e.g., due to a broken weld on the NGR), the monitoring device will sense voltage through the sensing resistor and ...
The Code gives rules for calculating circuit loading and maximum ampacity. Ground-fault circuit interrupter (GFCI) protection is required on receptacles in wet locations and locations where there exists an easy path for fault current to travel to earth. This includes all receptacles intended to service kitchen counter surfaces, crawl spaces at ...