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ElectricalGLOSSARY

RCD / GFCI

Definition

A residual current device (RCD) disconnects a circuit when the current leaving on the live conductors differs from the current returning on the neutral, a difference that indicates a leakage to earth. IEC 61008-1 covers RCDs without overcurrent protection (RCCBs) and IEC 61009-1 RCDs with integral overcurrent protection (RCBOs). A rated residual operating current of 30 mA is used for the additional protection of people, and an RCD may trip at any value between 50% and 100% of its rating, from 15 to 30 mA for a 30 mA device. IEC 60364-4-41 and its national versions, such as NF C 15-100 in France and BS 7671 in the United Kingdom, require 30 mA protection for socket-outlets rated up to 32 A in general use (NF C 15-100 extends it to all circuits in dwellings), and IEC 60364-7-711 requires it for exhibitions, shows and stands; in the United Kingdom, BS 7909 applies BS 7671 to temporary systems for entertainment. In North America the equivalent device is the GFCI (ground-fault circuit interrupter) to UL 943, whose Class A devices trip at 4 to 6 mA, and the NEC requires GFCI protection for 125 V receptacles on temporary wiring used by personnel during construction, maintenance or similar work (Article 590) and at carnivals, circuses and fairs (Article 525).

In the field

Electronic loads such as LED drivers and switch-mode power supplies leak a small current to earth through their filters, and many of them on one RCD can add up to a trip with no fault present. BS 7671 advises keeping the standing leakage downstream of an RCD below 30% of its rated residual current, about 9 mA for a 30 mA device. Large systems therefore spread the loads over several RCDs, and outdoor systems divide their circuits so that one trip does not black out the whole rig.

Related lessons

Electrical Safety→

Sources

  • IEC 61008-1 / IEC 61009-1 : RCCB et RCBO ; non-déclenchement à 0,5 IΔn, déclenchement à IΔn
  • Residual-current device (Wikipedia, pointeur secondaire) : principe du DDR et du GFCI · en.wikipedia.org
  • UL, Understanding Ground Fault and Leakage Current Protection, GFCI de classe A selon l'UL 943 : déclenchement entre 4 et 6 mA · code-authorities.ul.com
  • Schneider Electric, Electrical Installation Guide, Additional protection: High sensitivity RCDs, IEC 60364-4-41 : DDR ≤ 30 mA pour les socles d'usage général ≤ 32 A · electrical-installation.org
  • Legrand, NF C 15-100 : protéger les personnes avec des interrupteurs différentiels : protection différentielle 30 mA sur l'ensemble des circuits du logement · legrand.fr
  • IET Wiring Matters, Mythbusters #8, BS 7671 : protection complémentaire 30 mA exigée pour les socles de courant assigné ≤ 32 A, pas pour tous les socles · electrical.theiet.org
  • IEC 60364-7-711:2018 : installations électriques des expositions, spectacles et stands
  • IEE Wiring Matters, Exhibitions, Shows and Stands, section 711 de la BS 7671 : DDR 30 mA en protection complémentaire sur les circuits terminaux ≤ 32 A de prises et sur les circuits d'éclairage · electrical.theiet.org
  • BS 7909:2023+A1:2024 : installations électriques temporaires du spectacle, au sens de la BS 7671 · knowledge.bsigroup.com
  • Voltimum/NICEIC, Residual current devices, BS 7671 Reg. 531.3.2 : fuite permanente limitée à 30 % de IΔn (9 mA pour 30 mA) · voltimum.co.uk
  • EC&M, Keeping it Safe at Carnivals, Circuses, and Fairs, NEC article 525 : GFCI sur les prises 125 V de 15 et 20 A accessibles au public · ecmweb.com
  • NEC 590.6(A)(1) (texte reproduit) : GFCI sur les prises 125 V monophasées de 15, 20 et 30 A des installations temporaires utilisées par du personnel · electricallicenserenewal.com