Protective grounding is a specially made electrical connection to the ground of non-conductive metal parts, which, due to a short to the device’s case, may be energized. This occurs when the electrical connection of non-conductive metal parts of an electrical installation with live parts is accidental, voltage can also occur, for example, during a lightning discharge.
Using protective grounding eliminates the risk of electric shock when touching metal live parts or the equipment case, which, due to a short to the case, are under voltage.
It is necessary to distinguish protective grounding from the working one, which is intended for the correct operation of electrical installations, as well as from grounding for protection against lightning. To the worker include the grounding of neutral currents of the winding of the generator, power transformer and other devices.
For the grounding device, it is necessary to use natural devices and materials: metal and water pipelines that do not have an anti-corrosion coating, excluding pipelines with explosive and combustible gases or liquids. For grounding, lead cable sheaths, fittings and metal elements of reinforced concrete buildings or structures are suitable. It is only necessary to consider that such grounding must have a connection to the ground. In addition, metal tongues or casing pipes are suitable. But bare aluminum conductors and cable sheaths from this material are prohibited.
In the absence of natural grounding conductors or if they have a high resistance, artificial ones can be used with which they create protective grounding. They are made of pieces of angular steel 5x5x0.5 cm 2-3 meters long, the same size of steel pipes with a diameter of 5 cm, pieces of steel round (length up to 5 meters, diameter 12.0 - 14.0 mm). The used parts (electrodes) must be immersed in the soil at a distance of 3-5 meters from each other, all elements must be interconnected by a steel strip, the cross section of which is 40x4 mm.
The connecting strip is laid in a trench to a depth of 0.70 meters, at the same distance from the surface the upper ends of the electrodes are located. All elements are connected by welding. The number of electrodes is calculated based on the resistivity of the soil, the size of the electrodes, the depth of freezing and other factors.
Protective grounding of electrical installations with voltages up to a thousand V can be organized using metal structures of the building (in the presence of a reliable connection of all elements of the circuit), steel pipes for electrical wiring, aluminum sheaths of cables, metal pipelines (with the exception of central heating, gas and sewage). Also used are metal trays, boxes, busbar covers and zero wires of electrical circuits (protective grounding).
It is forbidden to use metal and lead thin sheaths of wires and cables as protective neutral conductors. Aerial AC networks are zeroed by means of a neutral wire, which is laid on the same supports as phase wires.
However, grounding does not always guarantee the necessary safety for a person in contact with an electrical installation. In some cases, in rooms with increased danger, along with grounding, re-protective grounding is used or protective shutdown is used. Protective neutral wires are not allowed to be used to zero electrical appliances that feed on other lines, as they can be turned off for repair.
Protective shutdown devices include circuit breakers that respond to current leakage. The use of these devices in apartments allows you to increase electrical safety.