Current of operation of the machine gun of protection has to be more, than consumed. The machine guns released by the industry are calculated on a standard number of rated currents of operation. Bigger next value makes of this row 30 A. Proceeding from it we will choose the machine gun of protection of type.
Let's carry out calculation of superficial grounding conductors of a neutral. According to PUE resistance of grounding of a neutral of the transformer at a voltage of 380/220 V should not exceed 4 Ohms. Resistance of each of repeated grounding conductors has to be no more than 10 Ohms.
Exclusively great value, for electrical safety the correct organization of service of the operating electroinstallations, carrying out repair, installation and scheduled maintenance has. Thus the correct organization is understood as strict performance of a number of organizational and technical actions and means.
The wrong organization of work leads to premature exhaustion because of an overstrain of separate bodies, irrational alternation of movements, their monotony. If on a workplace full safety is not guaranteed, it also causes premature exhaustion.
So that to provide the demanded resistance of repeated grounding conductors no more than 10 Ohms it is necessary to apply one vertical electrode and six vertical electrodes connected by a steel strip at the chernozem on the clay soil. Grounding conductors are executed from steel pipes 2,5 m long, with a diameter of 50 mm and are driven on depth of 7 m.
Let's choose the section of wires. At the greatest it is long to a permissible load for copper wires with rubber isolation 30 A (at ambient temperature 250C) section makes 2,5 mm the Section of aluminum wires under the same conditions - 4 mm
Let's define current of operation of the machine gun of protection. We assume that total power consumption measuring equipment, devices of lighting by both other installations and adaptations does not exceed 6 kW. Then the consumed current:
The design of a workplace provided optimum situation working, performance of labor operations within a reach zone, placement of governing bodies so that during the work as two hands was not their crossings.
where Uf - network tension; Rf and Rn - active, and Hf and Hn - internal inductive resistance phase and protective zero conductors respectively; - resistance of interinduction of a loop a phase - zero.
Security measures at operation of electroinstallations are indoors taken. Inaccessibility of current carrying parts to a casual touch is provided (all devices are in cases, all panels are blocked). Organizational actions are carried out. It is a personnel safety notification on workplaces, periodic quality check of grounding and resistance of isolation. Besides zeroing which calculation is given further is applied.
resistance of grounding of each of repeated grounding conductors (Rp) has to be no more than 10 Ohms, and in networks in which R0 is allowed, it can make 30 Ohms provided that number of repeated grounding conductors in this network not less than three;
As it is known it is easier to prevent the fire, than to extinguish. Therefore, it is necessary to provide all possible reasons of emergence of the fire and means for its suppression. Fire safety of the room is regulated by norms ONTP 24-86, category B, a room class on PUE-85 P-IIA, instructions on ensuring fire safety on separate objects. In our room are not stored and are not applied during the work flammable substances, and also there are no combustible liquids and gases therefore can be the reasons of emergence of the fire: malfunction or misuse of electric equipment, negligence of the working personnel on performance of fire-prevention actions.