Upper limit of current for relay protection devices

When the current load exceeds the the max limit of 5 A, the load is immediately disconnected. Plug Setting Multiplier (PSM) indicates how many times the determined relay secondary current (typically the CT secondary) exceeds the relay pickup (plug) current. It is the key quantity utilized in IDMT. In an electric power system, overcurrent or excess current is a situation where a larger than intended electric current exists through a conductor, leading to excessive generation of heat, and the risk of fire or damage to equipment. Possible causes for overcurrent include short circuits, excessive. Good and reliable selectivity of the protection is essential in order to limit the supply interruption to the smallest area possible and to give a clear indication of the faulted part of the network. This makes it possi-ble to direct the corrective action to the faulty part of the network and the. Faster clearing times are desirable whenever it is possible for the three reasons given above. Overcurrent protective devices at 480V are set to open at or below the downline cable or busway ampacity per NEC Section 240. Discrimination is achieved using a discrimination study, the ratios shown below or manufacturer's data and. Overcurrent protection devices can be categorized into three main types: Fuses are essentially made up of a metal wire or strip that melts when excessive currents flow through. Being such, fuses operate on a continuous-ampere rating.