A quick guide to Current / Time Characteristics of Protective Devices and RCDs

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Appendix 3: BS7671 (2015)

RCDs

From Table 3A Time / Current RCDs ‘disconnection times’
Non-delay:
  • Residual current of 1 x its rating = 300ms max
  • Residual current of 2 x its rating = 150ms max
  • Residual current of 5 x its rating = 40ms max

Delay ‘S’:

  • Residual current of 1 x its rating = 130ms min 500ms max
  • Residual current of 2 x its rating = 60ms min 200ms max
  • Residual current of 5 x its rating = 40ms min 150ms max

Circuit Breakers and RCBO

  • Protective Devices – Circuit Breakers BSEN 60898 Type B and also RCBOs BSEN 61009-1
    Fig 3A4: 5 x its rating for a 0.1 to 5 seconds disconnection time
  • Protective Devices – Circuit Breakers BSEN 60898 Type C and also RCBOs BSEN 61009-1
    Fig 3A5: 10 x its rating for a 0.1 to 5 seconds disconnection time
  • Protective Devices – Circuit Breakers BSEN 60898 Type D and also RCBOs BSEN 61009-1
    Fig 3A6: 20 x its rating for a 0.4 seconds disconnection time
    10 x its rating for a 5 seconds disconnection time

Fuses

Time current characteristics for fuses are found in the graphs and tables in BS7671 ‘see below’
BS 88-3:  Fig 3A1
BS 3036: Fig 3A2(a)(b)
BS 88-2: Fig 3A3(a)(b)(c)

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