Ground Fault Protection - engineering site - Schneider Electric

In shortTo ensure protection against fire:b the NEC defines the use of an RCDwith very low sensitivity called GFPb IEC 60 364 standard uses thecharacteristics of the TT systemcombined with low or high sensitivityRCDs.These protections use the same principle :fault current measurement using :b a sensor that is sensitive to earth faultor residual current (earth fault current)b a measuring relay that compares thecurrent to the setting thresholdb an actuator that sends a tripping orderto the breaking unit on the monitoredcircuit in case the threshold setting hasbeen exceeded.1.3. The role and functionsof “Ground Fault Protection”This type of protection is defined by the NEC (National Electrical Code) to ensureprotection against fire on electrical power installations.1.3.1. Earthing systemIEC standard:b uses ES characteristics to manage the level of fault currentsb for this reason, only recommends fault current measuring devices that have veryweak setting values (RCD with threshold, in general, < 500 mA).The NECb defines TN-S and IT systemsb recommends fault current protection devices with high setting values (GFP withthreshold, in general, > 500 A) for the TN-S system.Earthing Systemfault currentuse of ESb IEC 60 364b NECfire:b for IEC 60 364b for NECTN-CSystemstrongId y 20 kAbforbiddennot recommendednot applicableTN-SSystemstrongId y 20 kAb b bb b bnot recommendedGFP 1200 ATTSystemmediumId y 20 kAb bforbiddenIT-1st faultSystemweakId y 0.1 Abbrecommended + RCD 300 mAnot applicableb rarely usedb b used b b b often used1.3.2. RCD and GFPThe insulation fault current can:b either, cause tripping of Short-Circuit Protection Devices (SCPD) if it is equivalentto a short-circuitb or, cause automatic opening of circuits using specific switchgear:v RCD if the threshold setting value has high sensitivity (HS) 30 mA or low sensitivity(LS) up to 30 Av GFP for very low sensitivity setting values (> 100 A).DB117269