Protective Grounding - Zeroing the potential of conductive parts of an electrical installation that are not directly under the condition of working equipment. These parts include a metal case. Protective grounding is called for the reason that the neutral conductor is not required directly for the operation of the installation; it plays a role in the event of a breakdown or accident. In contrast to the worker, ensuring the proper functioning of electrical equipment.
Basic Terms and General Concepts
Grounding is rarely performed for 220 volt household circuits, according to standards adopted by the USSR.Exceptions are premises with increased danger( relative humidity above 75%, presence of concrete, brick, metal, earth floors, heat - above 35 degrees Celsius for more than one day, having metal pipes inside, water drains, other conductive currents and grounded structures).Imported equipment comes in accordance with other requirements. Grounding is necessary in all cases for proper operation of the input filters, screening harmful harmonics, protecting the network at home from interference. Characteristic:
- Washing machines.
- System units of personal computers, monitors.
- Refrigerators with electronic( non-mechanical) control.
- Microwave ovens( microwaves).
If the grounding( zeroing) is not performed, the house will be filled with interference, people's well-being will deteriorate, in some cases you can get an average force electric shock. Unpleasant, shock prick. It is necessary to be afraid, being near batteries, sinks, sinks, various water, gas metal pipes( including, painted).Cookers are grounded for another reason: a spark jumps onto the body during ignition of the burner. You can follow the instructions, it is not recommended to violate the instructions.
Grounding, as a zeroing, is not required for AC circuits with voltages below 42 volts, and DC circuits up to 110 volts. It refers to the case when the equipment is on a metal structure, firmly connected to the ground. Some sources state: it is prohibited to ground the equipment in three-phase circuits with a deaf-grounded neutral, if there is no grounding. In case of an accident, up to half of the phase voltage will be output. Not everyone understands the essence of the matter, it will be useful to decompose into points:
- The zeroing is to unite the body, the neutral.
- In a good three-phase circuit, a low current quota is applied to the neutral wire. And only with imbalances.
- Shrouded housing is relatively safe. Since the current of the accident through the person will flow moderate, with phase distortions.
- If the case is grounded, when the potential on the case goes out, the full voltage is applied to the person, in case of an accident.220 volt.
- Neutral combined with phases, during the breakdown of the potential, it is not a fact that the current will flow towards the deaf-grounded part through the human body. At other points the potential may be lower. For example, in the next phase. The current will go in that direction.
- As for the individual protective grounding, there is no other way - through the human body, with its consequences( death, electric shock).
For these reasons, three-phase installations with a dead-earthed neutral are forbidden to be equipped with a protective ground if there is no grounding. There is another meaning of the event. If typical circuits can be protected by a differential automatic, three-phase danger is presented from another direction. In everyday life, a leakage current is traced, a passing neutral signaling the danger( the human body).
The safety of equipment is considered important in the industry because the staff has passed safety tests. It is believed people can take care of themselves. Automatic protection of three-phase circuits track other signals, the main is the imbalance of the phases. The case considered above by points when there is a breakdown on the case. Of course, increased phase consumption is monitored. Others are determined by the type of three-phase circuit breaker, of which there is a great many in the technique. It is necessary to select for each case taken separately.
In circuits with insulated neutral, it is sometimes allowed to equip a protective earth. If the immediate shutdown of the equipment is not allowed, an additional tooling is carried out to check the insulation isolation test. If the protective vanishing or grounding of industrial facilities cannot be performed, the installations are serviced from sites isolated from the ground. Step voltage is taken into consideration, for metal structures it is small.
For the topic in question, you will find useful information in the Electrical Installation Guidelines. Today, the latest edition considers the seventh( 7), but those who are concerned about their own security should be guided by the outdated sixth version of the document. Many chapters of OLC are not legally required standards. Consider, as recommended by professionals, for those who wish to secure equipment and personnel.
Grounding is a more rigid measure than zeroing. A separate tire of low resistance is created, leading to a conductor buried in the ground, equipped according to the standards. Zanulenie limited to the combination of buildings with a dead-grounded neutral( or the corresponding output of the power source in single-phase networks).Resistance to ground is the length of the cable to the substation or generator. The magnitude is determined by many conditions. The maximum value of the resistance of the ground circuit is firmly defined by standards.
For domestic electrical systems, the requirements are loyal. The resistance of the ground circuit is less than 10 ohms. This is easily accomplished by using copper wires with any type of cores of different cross sections. For the design of specific systems, it is necessary to follow the tables containing information on the specific resistance of the samples. For copper wire residential cross-section of 0.5 square millimeters, the figure is 0.035 Ohms. The bay with a length of 100 meters will not reach a critical point. Requirements are tightened by these aspects:
- For installations with a voltage higher than 1 kV, the grounding resistance is chosen to be 0.5 Ohm. The verification of compliance with the criteria is carried out by measuring with a special tester. The device is multifunctional due to the high cost. The catalogs are under the name of the earth resistance meter.
- For generators, transformers, other sources, the grounding resistance varies depending on the voltage, is, respectively, for 220, 380, 660 volts - 8, 4, 2 Ohms.
There are other exceptions to the rule, the scrupulous master is required to be guided by official documents. GOST 12.2.007.0 informs about electrical safety equipment classes. Correspondingly, protective grounding is being arranged( classes O, OI, I), or is absent. The classification is used by many documents, it is useful to study the professional workers who are just wanting to properly, safely equip a dwelling.
On production, the use of protective grounding, zeroing is accompanied by additional measures of potential equalization. All metal structures, communications( pipes) are connected to the ground bus. It is recommended to do the same in bathrooms, kitchens of residential apartments. Previously it was not required, because communication pipes were made of galvanized steel, today plastic is being installed. There is a need for additional measures of protection. On production, it is required to ground( zero) the structures:
- Electric drives.
- Electrical Installation Enclosures with the exceptions mentioned above.
- Metal structures of communications: trays, gutters, pipes.
- Screens for low-voltage cables( up to 50 V AC, 120 V DC).
- Distribution boards and other similar types of structures.
The listed elements do not need protective grounding, zeroing:
- Enclosures for electrical equipment, elements of communications installed on metal grounded frames, in the presence of mutual reliable electrical contact.
- Metal fittings of various kinds, installed on wooden structures, pillars, unless otherwise required by other rules and regulations.
- Enclosures of electrical safety equipment class II and III.
- Places of inputs to buildings, passages through walls with a voltage of the route up to 25 V AC, 60 V DC.
Classes of premises and grounding
The authors consider: the grounding of household appliances is not difficult. If there is no special bus in the house, it is allowed( common wisdom, standards are prohibited) to use the neutral wire( carried out by appropriate commutation of the conductors inside the socket, combining with the appropriate lobe).On this subject, you can talk for a long time, instead we give a few rules that an electrician must strictly observe:
- Phase in the outlet is on the left. If necessary, the ground lobe is turned to the right( neutral).
- Subject to paragraph 1, the L-shaped plug of household appliances is inserted into the socket by tapping down.
- If you take the computer power filter in one hand for the cord, in the lowered splitter the phase is on the left( diagonally).
- In most of the equipment, the phase conductor is not different from zero, it will not be an error to insert the plug into the socket with the other side. The main thing is that the side lobe is set to zero.
At the production site, all electrical equipment is grounded regardless of voltage, places, installation methods, if we are talking about explosive rooms of any class. Ordinary citizens should be interested in the case when it comes to the garage.
- Zones B-I include those where saturated gases form explosive mixtures with air, even in the normal mode of operation of an object.
- В-Iа - Same as ВI, but with a significant reservation: the danger arises from an accident. The calculation is carried out according to GOST R 51330.9( other documents).If the name of the explosive class differs from the list given, a table of approximate conformity is sought.
- K-Ib adds a number of conditions. High lower limit of gas explosion( GOST 12.1.005), low danger. Or the presence of a strong smell. Natural gas is devoid of pronounced flavor. To indicate leakage, a special odorant is added to it. The owner of the apartment immediately notices the accident. Lowers the explosive class of the apartment. These include specialized production facilities with hydrogen circulation of more than 5% by volume, where an emergency situation is provided for by the ventilation operation.
- ВI-г - areas with outdoor installations, the rooms are not affected.
Other explosive hazardous substances are classified as Class B-II and below. Garage is considered a potentially explosive room, the operation of electrical equipment is fraught with risk.