To design the electrical installation of a residential building, the electrician designer must receive an output of the building characteristics, its size and obtain basic construction drawings: basement projections, attics, repeatable storeys, cross-section of the building, situational plan of the building's surroundings with the external electrical network marked on it.
The sequence of work in drawing up the project is as follows.
Depending on the type and size of rooms in the apartments, we select the type and number of lighting fittings as well as the number and type of plug sockets.
Then we choose the number of circuits. This number depends on it, whether the apartment is equipped with a gas pipeline installation, or not. The number of circuits may increase, if the number of sockets is greater than 10 or the number of projections greater than 20. A double or triple socket outlet should be counted as one socket.
We choose now, depending on the structure of the building and the adopted method of installation, type of conductors with cross-sections:
— for lighting spline circuits — 1,5 Mm2 Cu,
— for socket-outlet circuits — 1,5 mm2 or 2,5 Mm2 Cu.
We select the appropriate type and parameters of the protection. It is recommended to use circuit breakers as protection for residential circuits. As a protection against electric shocks, an automatic switch-off with the use of residual current devices should be used.
After arranging the equipment in the apartments, we make an installation plan, i.e. we draw the entire installation in the apartment with a division into circuits derived from the residential switchboard, most often located in the hall near the entrance door.
At the same time, we select branches from high-voltage and floor boards. Now you can select internal supply lines and branches from them to the apartments. Knowing the load already, we choose the number, cross-section and type of cable on visa. The number of visas depends on the number, the power and layout of the apartments. The visas can be made single-phase, if it is to supply a maximum of two consumer installations. If there are more apartments, visas should be designed as three-phase and connected in such a way, that the loading of the phases is even. The cross-section and the LV protection placed in the main switchboard are selected in accordance with the rules.