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An overcurrent relay is a type of protective relay which operates when the load current exceeds a pickup value. It is of two types: instantaneous over current (IOC) relay and definite time overcurrent (DTOC) relay. The ANSI device number is 50 for an IOC relay or a DTOC relay. In a typical application, the over current relay is connected to a ...
Device numbers may be combined if the device provides multiple functions, such as the Instantaneous / Time-delay Overcurrent relay denoted as 50/51. [ 3 ] For device 16, the suffix letters further define the device: the first suffix letter is 'S' for serial or 'E' for Ethernet.
50 – Instantaneous Overcurrent (N for neutral, G for ground current) 51 – Inverse Time Overcurrent (N for neutral, G from ground current) 59 – Over Voltage; 62 – Timer; 64 – Ground Fault (64F = Field Ground, 64G = Generator Ground) 67 – Directional Over Current (typically controls a 50/51 element) 79 – Reclosing Relay
Instantaneous overcurrent requires that the current exceeds a predetermined level for the circuit breaker to operate. Time overcurrent protection operates based on a current vs time curve. Based on this curve, if the measured current exceeds a given level for the preset amount of time, the circuit breaker or fuse will operate.
A relay allows circuits to be switched by electrical equipment: for example, a timer circuit with a relay could switch power at a preset time. For many years relays were the standard method of controlling industrial electronic systems. A number of relays could be used together to carry out complex functions (relay logic). The principle of relay ...
Pages in category "Over-current protection devices" The following 12 pages are in this category, out of 12 total. ... Protective relay; R. Resettable fuse
An optional time delay circuit that controls the timing of the switch action after the input has reached the threshold; A power supply for the static relay circuits; For example, an overcurrent protective relay may have an AC to DC power supply for the input circuit, a level detector circuit and an RC time delay circuit. [1]
According to the 2020 NEC/NFPA 70, a current-limiting overcurrent protective device is defined as, "A device that, when interrupting currents in its current-limiting range, reduces the current flowing in the faulted circuit to a magnitude substantially less than that obtainable in the same circuit if the device were replaced with a solid ...