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. F100 – 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
(IEC 60364-4-42) |
Protection against overcurrent
(IEC 60364-4-43) | ||
|---|---|---|---|---|---|
| Basic protection | Automatic disconnection | Additional protection | BE2 location[a] or locations where consequences of fire are severe | ||
| TNC | Insulation of live part / Barriers & enclosure | OCPD | NA | TNC forbidden in these locations | OCPD (overload and short-circuit) |
| TNS | OCPD/RCD | RCD 30mA | 300mA RCD + AFDD[b] | ||
| TT | RCD | RCD 30mA | |||
| IT | OCPD/RCD | RCD 30mA | |||
- OCPD: overcurrent protective device
- RCD: Residual current device (Sensitivity in the range 30mA – 30A )
- AFDD: Arc Fault Detection and Protection Device
- ^ 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).
- ^ In these locations, AFDD is mandatory for final circuits with one or more socket outlets. It is recommended for other circuits. The RCD <= 300 mA is mandatory for all circuits.
