soprano1085 wrote: so do you think that this scheme from "castorama" was developed by someone not competent ??
I was just following him and I was convinced that no one was doing this scheme
So what do you think? that the four-track FR is redundant and the C20 is also redundant ?? and if so, why ??
Please correct your spelling. [kkas12]
The schema is correct. Your connection is incorrect, because you connected the protectors before the FR and they are to be placed behind it.
The way of connecting FRs, miniature circuit breakers and arresters from above or below does not matter.
It is important only for some cameras, including RCDs, but you probably won't find such ones in Castorama.
As far as the C20 is concerned, it is not superfluous, on the contrary, it is very much needed. This is called backing up protectors. It works in such a way that when an overvoltage occurs in the arrester, a short-circuit occurs and the excess charge is brought to the ground through the PE protective circuit (i.e. the PE strip, the PE conductor connecting to the GSW, the ground conductor and the earth electrode).
The protectors can absorb a certain amount of energy and give it back to the environment in the form of heat. Part of the overvoltage energy is also released as heat in PE conductors.
However, at the time of discharge, an ionized channel is formed in the arrester through which, apart from the surge current, the short-circuit current of the network also begins to flow. If there was no such protection of the arresters, this short-circuit current could cause complete damage to the arrester in which the discharge occurred before the circuit breaker in the terminal disconnects the entire supply circuit. The additional protection disconnects the circuit of the arresters, limiting the amount of energy released in the arrestor as a result of the short-circuit current flow, and thus protects quite expensive arresters against their complete damage.
Moreover, if there were no additional protection of the arresters, in the event of damage to the arrester insert, you would not be able to turn on the protection in the junction box, because this protection would be disconnected all the time due to a short circuit in the protector.
So do as you have in this diagram and it will be OK, as long as the security values in this diagram match the values given in your installation design. These in turn depend on the agreed power allocation with the energy sector and the cross-sections of the cables in the installation. Back-up protection is selected according to the type of arrester and its characteristics.
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