Protection against electrical fire risks - synthesis

From Electrical Installation Guide

In addition to protection against electric shock, protection against fire is another main target of a proper design of electrical installation. The minimum requirement is the coordination between overcurrent protective device and conductor permanent and short-time withstand. (See Chapter Sizing and protection of conductors ). But other protective measures are recommended to reduce the risk of fire due to electrical installation.

  • For main circuits and distribution circuits, more sensitive earth fault detection than the one necessary for protection against electric shock is recommended.
  • For terminal circuits where mechanical withstand of conductor is lower, where the number of connection is higher, where portable equipment can be supplied, in addition to RCD, Arc fault detection device is recommended.

The table below tries to position the different types of current-based protections required or recommended for low voltage installations.

Fig. F95 – Overview of current based protection of low voltage circuit according to earthing system
Earthing system Protection against electric shock

(IEC 60364-4-41)

Protection against thermal effect / Fire Protection against overcurrent

(IEC 60364-4-43)

Basic protection Automatic disconnection Additional protection BE2 location[a] Other location
Terminal Circuit Distribution Circuit
TNC Insulation of live part / Barriers & enclosure OCPD NA NA NA RS GFP[b] OCPD (overload and short-circuit)
TNS OCPD/RCD RCD 30mA 300mA RCD
AFDD
AFDD[c] RCD[c]
TT RCD RCD 30mA AFDD[c] RCD[c]
IT OCPD/RCD RCD 30mA AFDD[c] RCD[c]
  • in bold = mandatory according to IEC60364
  • in italics= recommended to improve protection against fire risks
  • OCPD: overcurrent protective device
  • RCD: Residual current device (Sensitivity in the range 30mA – 30A )
  • RS GFP: Residual Sensing ground fault protection[1](Sensitivity 20% -100% circuit breaker rating)
  1. ^ BE2: Locations with risks of fire due to the nature of processed or stored materials (according to Table 51A of IEC 60364-5-51:2005).
  2. ^ GFP is not described as such by IEC 60364 but is commonly used in some regions like North America
  3. ^ 1 2 3 4 5 6 RCD may be already required for protection against electric shock in that case it will contribute to protection against risk of fire

Notes

  1. ^ Cf. paragraph Ground fault protection.
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