To design the electrical installation of a building, the electrician designer needs to obtain detailed information on the building's characteristics, its size and purpose, and receive basic construction drawings: basement projections, attics and individual floors as well as the cross-section of the building and the situational plan of the building's surroundings with the external electrical network.
The sequence of work in drawing up the project is as follows.
Depending on the type, the size and purpose of the rooms, we select the type and type of lighting fittings as well as the number and type of socket outlets. The number of luminaires and their arrangement is determined based on the calculations performed using one of the methods. Then we select the number of lighting circuits. The number of circuits should be this, that the number of projections per circumference is no more than: 20 - in the case of incandescent lamps, 30 - in the case of fluorescent luminaires.
The number of circuits supplying plug sockets should be the same, that the number of sockets per one circuit is not greater than 10. 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 wires:
— for the circuits of lighting outlets — with a cross-section 1,5 Mm2 Cu,
— for circuits of plug sockets — with sections 1,5 mm2 or 2,5 Mm2 Cu.
According to the rules, we select the appropriate type and parameters of the security.
After arranging the equipment indoors, we make an installation plan, i.e. we draw the entire installation with a division into circuits derived from the switchgear, most often located in the corridor in the vicinity of internal power lines.
Usually a large number of computers are to be used in offices. In such a case, it requires designing a special installation powering computers separate from other installations. It is very often necessary to power specific groups of computers from the same phase.
Internal feed lines can now be selected, starting with the calculation of their loads. Knowing the load already, we choose the number, cross-section and type of incoming cable. The number of wlz depends on the number, power and layout. WLz should be designed as three-phase, and connect individual consumer circuits like this, that the loading of the phases is even. The cross-section of the wires should be selected in accordance with the rules.
At the same time, we select multi-storey switchgears.
Then we choose the type of wires, selection of the cross-section and protection.
The protections are placed in the main switchboard of the building.
The same way, if there are force checks, we select connectors, wires and protection of power circuits. We place the protection of the power installation in the main switchboard of the building.
Still calculations should be checked, if in the designed installation the voltage drops in the normal operating conditions of the installation do not exceed the values given in the tables. The individual voltage drops may be exceeded provided that the sum of the allowable voltage drops is not exceeded. It still needs to be checked, whether the conditions resulting from the applied electric shock protection will be met.
After all the previously discussed calculations have been made, we proceed to the drawing of the electrical wiring diagram of the building, covering the connection section, connector, and ended with energy receivers. We mark the meters in the connection diagram, switchboards (type), fuses (type and size), the number and power of individual load circuits, type, the number and cross-section of conductors and the method of routing them.