Our whole life is inseparable from all sorts of electrical appliances.Failure of any electrical equipment - a frequent and quite normal, no device can not work forever, and without a single failure.Our task - to protect these electrical helpers short circuit or overload occur in the chain, and themselves - from damaging the body's high voltage.In the first case, to the aid of all sorts of protective devices, but for the protection of human use of electrical grounding and vanishing.This is one of the most difficult parts of the electricians, but we 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 ↑
If machines, cork and other protective devices do not work on the malfunction, and the result is a breakdown of internal insulation onmetal casing installation overvoltage occurs.Touching a person of such a device can lead to paralysis of the muscles (at a current 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 technical features should be live, then they are sure to enclose them in accordance with the generally accepted safety measures, such as special covers, barriers or obstacles mesh.In order to prevent accidental electric shock if damaged insulation layers, use of protective grounding and vanishing.To understand the difference between the grounding of vanishing, need to know what they are.
What grounding ↑
often begins electricians do not quite understand what is the difference vanishing from the earth.Grounding - a connection to the electrical ground in order to reduce contact voltage to a minimum.It is used only in networks with isolated neutral.The installation of the equipment grounding much of the current supplied to the body, must go on the ground of the resistance which must be less than the remaining sections of the circuit.
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 purpose.When using the earthing resistance with high fault current can be too small to trigger the protective devices and installation of emergency will remain energized, posing great danger to humans and animals.
earthing conductors forms a grounding device, where it is, in fact, is the conductor (group of conductors) connecting conductive parts of installations to the ground.By appointment, these devices are divided into the following groups:
- lightning to discharge lightning surge current.Used for earthing and lightning arresters;
- workers to maintain the desired mode of operation of electrical installations, both in normal and in emergency situations;
- protection to prevent damage to living organisms electrical shock resulting from the breakdown of the phase conductor to the metal enclosure.
All grounding divided into natural and artificial.
- natural - it is piping, steel reinforced concrete structures, casings and others.
- Artificial grounding - a structure being built specifically for this purpose, ie, steel bars and strips, angled steel pipes and other sub-standard.
Classification of grounding ↑
Depending on the wiring and the number of zero workers and protective conductor can be divided into the following electrical grounding system:
first letter in the name of the type of said ground power source:
- I - live parts are completely isolated from the ground;
- T - neutral power supply is connected to ground.
In the second letter, you can determine how earthed exposed conductive parts of the installation:
- N - direct connection to the grounding point source;
- T - direct contact with the ground.
letters, standing just behind the N, with a hyphen, say, a device PE Protective and work N Neutral conductor:
- C - function conductor provides one conductor PEN;
- S - function guides provided by different conductors.
Outdated TN-C ↑
Such grounding of electrical use in single-phase and three-phase four-wire networks that dominate the buildings of the old sample.Unfortunately, this system, despite its simplicity and accessibility, can not achieve a high level of electrical safety and on newly constructed buildings is not applicable.
to modernize old houses TN-CS ↑
Protective earth Electrical this type is mainly used in the reconstructed networks, where the working and protective conductors integrated in the opening circuit device.In other words, this system is used in the case of an old building where the operated grounding type TN-C, will be located computer equipment or other telecommunications, i.e. to effect the transition to the system TN-S.This relatively inexpensive scheme has a high level of security.
Specificity of TN-S ↑
This system is different location zero and the working conductors.Here they are run separately, with protective earth 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 the minimum length of a conductor from the cable entry to the electrical system to the grounding device.
system TT, especially ↑
system where all live exposed parts directly connected to the ground, the earth electrode have no electricity, depending on the neutral earthing substation, called TT.
Characteristic differences of IT ↑
difference of this system is to isolate the neutral power supply from the ground or through the grounding device with great resistance.This method allows you to minimize the leakage current on the body or in the ground, so it is best used in buildings, where there are strict requirements on electrical safety.
What vanishing ↑
vanishing - this compound metal parts, not energized or grounded neutral down the source of three-phase current or a grounded single-phase generator output current.It is used for the breakdown of the insulation and the current hit any dead parts device, a short circuit, leading to a rapid triggering of a circuit breaker, a blown fuse or reactions of other security systems.Mainly used in electrical installations with earthed neutral.
Additional installation RCD line will cause it triggered as a result of the difference in the strength of the current phase and the neutral conductor.If they are installed and the RCD, and the circuit breaker, the sample will trip or both devices or to the inclusion of a high-speed element.
Important: When installing vanishing, be aware that the short circuit current must be as high as the melting insert the fuse or circuit breaker, otherwise free flow of fault current through the circuit will cause the voltage on the vanishing of all cases, not just the damaged area.And the value of this voltage is equal to the product of the resistance of the neutral conductor to the fault current, and therefore extremely dangerous for human life.
the serviceability of the neutral wire is necessary to monitor very carefully.Its open circuit voltage gives rise to all vanishing housings, as they are automatically connected to the phase.That is why the installation is strictly prohibited in the neutral conductor of any means of protection (breakers or fuses), forming his break when triggered.
In order to reduce the likelihood of damage to the shock when the neutral conductor is broken, every 200 m line is executed repeatedly ground.Similar measures have been taken to limit and input support.The resistance of each re-earthing shall not exceed 30 ohms, and the total resistance of all ground connections - 10 ohms.
vanishing and ground: what is the difference?↑
main difference between zeroing and the ground is that the grounding safety is ensured rapid decline in voltage, while Vanishing - disconnection of the chain, which had a sample of the current on the body, or any other part of the power plant, while in the interval betweenclosure and termination of the power supply there is a reduction potential of body electrical systems, otherwise pass through the human body a shock.
requirements for grounding (vanishing) ↑
All electrical installations where the neutral is isolated, be sure to perform protective grounding and should be possible to quickly search the earth fault.
If the device is earthed neutral, and its voltage is less than 1000, you can only use 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 consumers with a nominal current of the protective device no more than 15 A. In this case, the grounding is prohibited or vanishingsecondary winding.
If a neutral three-phase up to 1000 in an isolated, these installations should be protected from breakdown due to damage to the insulation between the windings of the transformer and fuse breakdown, which is mounted in a neutral or phase from the lower voltage.
what and when must be grounded ↑
Protective grounding and vanishing electrical should be carried out in the following cases:
- When an alternating nominal voltage of more than 42 V and continuous rated over 110 highly dangerous and outdoor installations.
- When AC voltage of more than 380 permanent and over 440 in all installations.
grounding housing electrical, drive units, frames and metal structures of cabinets and boards, the secondary windings of transformers, metal sheaths of cables and wires, cable design, busways, ducts, cables, steel pipe wiring and electrical equipment, located on the moving parts.
in public buildings necessarily subject to vanishing (grounding) electrical capacity of more than 1300 watts.If the ceilings are made of metal, it is necessary to ground all metal housing lighting.Bathtubs and shower trays made of metal, should be connected with water pipes metallic conductors.This is done to equalize electrical potential.For housing ground air conditioners, electric stoves and other appliances whose power exceeds 1300 W, using a separate wire that is attached to the mains neutral conductor.Its cross-section and the cross section of the phase conductor, laid on the switchboard, should be equal.
A complete list of equipment requiring earthing or neutralization, as well as devices, where on the contrary, is permitted to ignore these protection measures can be found in the SAE (electrical codes).Here you can find all the basic rules of electrical grounding.
device grounding and vanishing - this is a very demanding job.The slightest miscalculation or neglect seemingly insignificant one requirement can lead to a great tragedy.Perform grounding are required only to people who have the necessary knowledge and experience.