RCDs are very effective devices to provide protection against fire risk[1] due to insulation fault because they can detect leakage currents (ex : 300 mA) which are too low for the other protections, but sufficient to cause a fire. //

Some tests have shown that even a fault current as low as 300 mA can induce a real risk of fire (see Figure F74) //

For TT, IT and TN-S systems the use of 300 mA sensitivity RCDs provides a good protection against fire risk due to this type of fault. //

The IEC 60364-4-42:2010 (clause 422.3.9) makes it mandatory to install RCDs of sensitivity ≤ 300 mA in high fire-risk locations (locations with risks of fire due to the nature of processed or stored materials - BE2 condition described in Table 51A of IEC 60364-5-51:2005). TN-C arrangement is also excluded and TN-S must be adopted. //

In TN-C system, RCD protection cannot be used, as the measurement of earth fault current by a sensor around line conductors and PEN will lead to permanent wrong measurement and unwanted trip. But a protection less sensitive than RCD but more sensitive than conductors’ overcurrent protection can be proposed. In North America this protection is commonly used and known as “Ground Fault Protection”.