Grounding and electrical vanishing
Our whole life is inseparable from all sorts ofelectrical appliances. Failure of any electrical equipment - is frequent and quite normal, no machine can not run forever, and without a single failure. Our task - to protect these electrical helpers short-circuit or overload occur in chains, and themselves - from damaging the body's high voltage. In the first case, to the aid of all kinds of protective devices, but use of electrical grounding and vanishing for human protection. This is one of the most difficult parts of the electrical, but we will try to figure out what is the difference between these works, and in what cases it is necessary to apply certain protective measures.
- Means of protection against electric shocks
- What is the ground
- Classification of earthing systems
- Outdated system TN-C
- For the modernization of old houses TN-C-S
- The specifics of the system TN-S
- TT system features
- Characteristic differences between IT systems
- What is vanishing
- The vanishing and ground: what is the difference?
- Grounding Requirements (vanishing)
- What and when you need to be grounded
Means of protection against electric shocks
If machines, cork and other protectivedevices do not work on the malfunction, and the result is a breakdown of the internal insulation, install a metal housing overvoltage occurs. Touching a person of such a device can lead to paralysis of the muscles (and the amperage of 20-25 mA), prevents the self-isolation from contact, arrhythmia, disorders of blood flow (at 50-100 mA) and even death.
If the power plant due to technicalfeatures should be live, then be sure to enclose them in accordance with standard safety equipment, such as special covers, mesh barriers or obstacles. In order to prevent accidental electric shock if damaged insulation layers, apply a protective grounding and vanishing. To understand the difference between the ground from vanishing, you need to know what they are.
What is the ground
Most beginners do not really understand electricians inWhat is the difference vanishing from the earth. Grounding - this electrical connection with the ground in order to reduce to a minimum the touch voltage. It is used only in networks with isolated neutral. As a result, most of the current installation of equipment grounding, coming on the case, must go on earthing of the resistance which must be less than the rest of the chain sections.
But this is not the only function of the ground. Protective earthing of electrical installations also increases the fault current circuit, as it may be contrary to its intended purpose. When using a high resistance grounding fault current value may be too small to trigger the protective devices and installation in an emergency will remain energized, posing a great danger to humans and animals.
Earthing conductor forms a groundingdevice, where it is, in fact, is the conductor (group of conductors) connecting conductive parts of installations to the ground. Upon designation of these devices are divided into the following groups:
- lightning, to divert the lightning current pulse. Used for grounding and lightning arresters;
- workers to maintain the desired operating mode of electrical installations, both in normal and in emergency situations;
- protection to prevent damage to living organisms electric shocks arising in the breakdown of the phase conductor to the metal enclosure.
All grounding conductors are divided into natural and artificial.
- Natural - a piping, steel reinforced concrete structures, casings and other.
- Artificial grounding - a structure being built specifically for this purpose, that is, steel bars and strips, angled steel, pipes and other sub-standard.
Important: for use as a natural ground is not suitable for pipes of flammable liquids and gases, a pipe coated with anticorrosive insulation and aluminum conductors and cable sheathing. Never use a grounding conductors in a residential area for water and heating pipes.
Classification of earthing systems
Depending on the connection method and the number of zero protective conductor and workers can be divided into the following electrical grounding system:
The first letter in the name of the system says about the type of power source ground:
- I - live parts are completely isolated from the ground;
- T - a neutral power source is connected to ground.
In the second letter, you can determine how earthed exposed conductive parts of the installation:
- N - immediate connection with the point of the power supply ground;
- T - direct contact with the ground.
Letters, standing just behind the N, with a hyphen, talk about the process of PE protective devices and desktop N zero conductor:
- C - wire functions are provided by a single conductor PEN;
- S - wire functions are provided by different conductors.
Outdated system TN-C
Such electrical grounding usedthree-phase four-wire and single-phase two-wire networks that dominate the old-style buildings. Unfortunately, this system, in spite of its simplicity and accessibility, can not achieve a high level of electrical safety and on newly constructed buildings, does not apply.
For the modernization of old houses TN-C-S
Protective earthing of electrical installations of this typeIt used mainly in the reconstructed networks, where the working and protective conductors are combined in the opening device circuitry. In other words, this system is used in the case of an old building where the grounding-type TN-C is operated, will be located computer or other telecommunications equipment, ie the transition to the system TN-S. This relatively inexpensive scheme has a high level of security.
The specifics of the system TN-S
Such a system zero position differsworking conductors. Here they are installed separately, and the protective conductor PE connects directly all conductive parts of the installation. To avoid re-ground, enough to arrange a transformer substation having a basic grounding. Moreover, such a substation allows for a minimum length of the conductor from the cable entry to the electrical installation to the grounding device.
TT system features
System, where all live exposed partsdirectly connected with the ground, and the earth electrode have no electricity, depending on the neutral earthing substation, called TT.
Characteristic differences between IT systems
The difference of this system is to isolate the neutralpower supply or from the ground via grounding device with a large resistance. This method makes it possible to minimize the leakage current on the body or in the ground, so it is better to use in buildings, where stringent electrical safety requirements are established.
What is vanishing
The vanishing - a compound of metal parts,not under stress or with grounded neutral three-phase step-down power supply or with a grounded single-phase current output of the generator. It used to the breakdown of the insulation and in contact with the current on any dead parts device, a short circuit, leading to a rapid triggering of the circuit breaker, blown fuses or other protection systems response. Mainly used in installations with earthed neutral.
Additional installation of an RCD on the line will lead toit triggered as a result of the difference between the current strength in phase and neutral conductor. If they are installed and the RCD and circuit breaker that will trip the sample or both devices, or to include a high-speed element.
Important: When installing zeroing must be borne in mind that the short-circuit current must reach the melting insert values fuse or circuit breaker, or the free flow of fault current through the circuit will cause the voltage on all vanishing buildings, and not only on the damaged site. And the value of this voltage is equal to the product of the zero conductor resistance at the fault current, and therefore extremely dangerous for human life.
For serviceability of the neutral conductor must bewatch carefully. Its open circuit voltage gives rise to a nulling all cases, as they are automatically connected to the phase. That is why the installation is strictly prohibited in the neutral conductor of any protection (circuit breakers or fuses), forming his break when triggered.
In order to reduce the likelihood of damagecurrent in case of interruption of the neutral conductor, every 200 m line is re-executed ground. The same measures are taken to limit and input support. The resistance of each re-earthing should not exceed 30 ohms, and the total resistance of all such grounding - 10 ohms.
The vanishing and ground: what is the difference?
The main difference between zeroing and groundingis that by grounding the safety provided by a rapid decrease in voltage, while Vanishing - disconnecting circuit area in which there was a breakdown of the current case or any other part of the power plant, while in the period of time between the closure and the termination of the power supply occurs casing potential reduction electrical, otherwise the discharge electric current will pass through the human body.
Grounding Requirements (vanishing)
All electrical installations where the neutral is isolated, be sure to perform protective grounding, and should provide the ability to quickly search for ground faults.
If the device is earthed neutral,and its voltage less than 1000 V, it is only possible to apply vanishing. When equipped with a separating electrical transformer secondary voltage must be no more than 380, the down - no more than 42 V. In this case, by separating the transformer is allowed to eat only one power-consuming equipment with a protective device rated current not exceeding 15 A. In this case, the prohibited ground or vanishing the secondary winding.
If a neutral three-phase up to 1000 Visolated, these installations should be protected from breakdown due to damage to the insulation between the windings of the transformer and the breakdown fuse that is mounted in the neutral or phase from the lower voltage.
What and when you need to be grounded
Protective grounding and vanishing electrical installations must be performed in the following cases:
- When AC rated voltage more than 42 V and a constant nominal over 110 particularly dangerous and outdoor installations.
- When alternating voltages above 380 V and 440 V constant over any installations.
Electrical grounding body, drivesmachines, frames and metal structures control cabinets and switchboards, secondary windings of transformers, metal sheaths of cables and wires, cable design, trunking, ducts, cables, steel pipe wiring and equipment located on the moving parts of machinery.
In public buildings certainlysubject to the vanishing of (ground) electrical appliances more than 1,300 watts. If the ceilings are made of metal, it is necessary to ground all metal body lighting. Bathtubs and shower trays made of metal, should be connected to the water pipes of metal conductors. This is done to equalize electrical potential. To ground the enclosure air conditioners, electric stoves and other appliances whose power exceeds 1300 W, applies a separate wire that is attached to the neutral conductor mains. Its cross-section and cross-section of the phase conductor, laid on the switchboard, should be equal.
A complete list of equipment requiringground or vanishing, as well as devices, where on the contrary, may be disregarded by these protective measures can be found in the SAE (electrical codes). Here you can find all the basic rules for electrical grounding.
The device grounding and vanishing - this is a veryresponsible work. The slightest miscalculation or neglect, it would seem, one minor requirement may lead to a great tragedy. Perform grounding obliged only people who have the necessary knowledge and experience.