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An insulation monitoring device monitors the ungrounded system between an active phase conductor and earth. It is intended to give an alert (light and sound) or disconnect the power supply when the resistance between the two conductors drops below a set value, usually 50 kΩ (sample of IEC standard for medical applications). The main advantage ...
A GCM or ground continuity monitor (also called a ground integrity monitor or ground continuity tester) is an electrical safety device that monitors the impedance to ground of a temporary electrical circuit and can provide indication (or protective trip) in the event impedance rises to an unsafe value. A GCM is either an external testing device ...
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.
Provide a relatively low-impedance path to ground, thereby maintaining the system neutral at or near ground potential. [3] Limit the magnitude of transient over voltages when restriking ground faults occur. Provide a source of ground fault current during line-to-ground faults. Permit the connection of phase-to-neutral loads when desired. [2]
A wire break in the fault to load section, or in the earth to ground section, will disable operation of the ELCB. Requirement of an additional third wire from the load to the ELCB. Separate devices cannot be grounded individually. Any additional connection to Earth on the protected system can disable the detector.
Earth fault protection also requires current transformers and senses an imbalance in a three-phase circuit. Normally the three phase currents are in balance, i.e. roughly equal in magnitude. If one or two phases become connected to earth via a low impedance path, their magnitudes will increase dramatically, as will current imbalance.
Three-phase transformers and their associated neutrals are usually found in industrial distribution environments. A system could be made entirely ungrounded. In this case a fault between one phase and ground would not cause any significant current. Commonly the neutral is grounded (earthed) through a bond between the neutral bar and the earth bar.
The three-wire and four-wire designations do not count the ground wire present above many transmission lines, which is solely for fault protection and does not carry current under normal use. A four-wire system with symmetrical voltages between phase and neutral is obtained when the neutral is connected to the "common star point" of all supply ...