Measures of protection against fire risk with RCDs
From Electrical Installation Guide
| RCDs are very effective devices to provide protection against fire risk due to insulation fault because they can detect leakage current (ex : 300 mA) which are too low for the other protections, but sufficient to cause a fire |
RCDs are very effective devices to provide protection against fire risk due to insulation fault. This type of fault current is actually too low to be detected by the other protection (overcurrent, reverse time).
For TT, IT TN-S systems in which leakage current can appear, the use of 300 mA sensitivity RCDs provides a good protection against fire risk due to this type of fault.
An investigation has shown that the cost of the fires in industrial and tertiary buildings can be very great.
The analysis of the phenomena shows that fire risk due to electicity is linked to overheating due to a bad coordination between the maximum rated current of the cable (or isolated conductor) and the overcurrent protection setting.
Overheating can also be due to the modification of the initial method of installation (addition of cables on the same support).
This overheating can be the origin of electrical arc in humid environment. These electrical arcs evolve when the fault current-loop impedance is greater than 0.6 Ω and exist only when an insulation fault occurs. Some tests have shown that a 300 mA fault current can induce a real risk of fire (see Fig. F26).
Some tests have shown that a very low leakage current (a few mA) can evolve and, from 300 mA, induce a fire in humid and dusty environment.
Fig. F26: Origin of fires in buildings
