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Electrical fireWhy this fires...2

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Why are there still all these fires ?


This being said, let's briefly enumerate the state of the currently used techniques: That which can produce heat susceptible to create a favorable condition to ignite a fire, and how the obligatory protection devices are suppose to protect us from them. We will refer to installations which are "up to code", achieved in a clean manner, and with protection devices in proper working order.


a) The Over-current (over-intensity):

For example, when too many and/or too powerful devices are plugged into a multi-outlet strip and then connected to only one electric receptacle. It could entail the heating-up of the circuit (Joule effect) but the over-current protection device at the head of the circuit limits the quantity of current entered (the breaker trips or the fuse blows).

There is a permanent surveillance and an automatic opening of the circuit with the fault.
This risk is adequately controlled, and it is rare that this phenomenon can create a fire. Fires due to extension cords and multi-outlet strips are most often due to the heating-ups of their connections.

b) "Direct" short-circuits:

It is when a direct fault contact occurs between the Phase and the Neutral. The quantity of current created in the instant is considerable; the over-current protection device opens the circuit at that instant.

Here we also find a permanent surveillance and an automatic opening of the circuit with the fault.
This risk is therefore adequately controlled, and it is because of this that a short circuit is never responsible for a fire or it is very rare.












c) "Slow" short-circuits:


It is while a faulty contact progressively forms between the Phase and the Neutral, which is what happens most often in devices, small transformers, etc. It is a dangerous phenomenon, the current must often pass some insulation and it incurs heat. Contrary to a "direct" short circuit, the temperature often increases progressively, yet slowly, and it will be necessary to wait until the intensity (current) passes the amperage value of the over-current protection of the circuit for the phenomenon to be stopped. This means that the favorable conditions to ignite a fire is often created and it can be too late. But a good number of devices are equipped with small fuses or
other thermal security devices to react more quickly.

There is a permanent surveillance and an automatic disconnection of the fault. It is not always sufficient, but one could consider that this risk is adequately controlled for the most part.


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