System of a country house Ground: variety, difference and Features
About how important to the private home or cottage is correctly installed earthing system has already been said a lot. Therefore repeat of the danger of electrical shock in the house is not connected to the grounding circuit, no special needs. And if you want to ensure the maximum security of your living space, the information set forth in this article, will no doubt be useful to you.
Grounds for private homes
Depending on the design features suitable to the house power lines different grounding systems are used. There are the following varieties: TN-S, TN-C, TN-C-S, TT, etc... Private houses and cottages is usually connected to the grounding system of two types: TN-C-S and TT. And if your house is not groundingThen these systems is easiest to put into practice, it is their many craftsmen create their own, it is about them and will be discussed in this article.
Briefly explain the meaning of the letters in the name systems:
- The first character indicates the grounding on the power supply parameters (eg, T - land).
- The second symbol (N or T) characterizes parameters grounding exposed parts of electrical household. The letter N, for example, denotes a neutral grounding or connection of the protective conductor with a home electrical power supply neutral point (substation).
- Letters S and C denote subspecies system in which the grounding is performed via the power source.
Simply put, if the first letter in the designation are TN, we are talking about a system with deaf grounding source supply and electrical system consumer to append it neutral by zero and protective conductors. As we have said, the grounding system there are several varieties:
- TN-C - system with combined neutral and protective conductor. Supply line in this case consists of a two- or four-wire are (phase and neutral conductors - single-phase power supply system, three phase and one zero - in a three-phase system electricity). TN-C system can hardly be called a full ground system, because electrical grounding conductors therein are connected to the neutral conductor coming from the transformer. Usually it is called zeroing, because how to perform all the functions of the grounding circuit is hardly capable.
- TN-S - system having separated neutral and protective conductor. Supply line in this case consists of three or five conductor cable (phase, neutral and protective conductor - in single-phase power supply system, three phase plus neutral and protective conductors - a three-phase system electricity).
- TN-C-S - system in which the neutral and protective conductor combines its function only on a particular portion which begins near the power supply and ends at the input to the house. Here they are separated at the protective earth (PE) and the neutral (N) conductor (shield conductor in such a system is subjected to re-ground). Essentially, TN-C-S system is created on the basis of TN-C.
- TT - a system in which a home power supply system has a separate ground blind that is not connected to the ground power supply substation.
Earthing in all categories TN systems is made through a transformer substation, while the TT system involves the creation of a ground loop is directly outside the house. One can argue about which of the two systems is better - TN-C-S or TT? Therefore, immediately denote the pitfalls of these two systems.
If you are thinking about creating a system TN-C-S, the first thing to be sure of the reliability of power transmission line, a supply electricity to your home. After all, as a rule, the state-of-town power lines (and they are, in most cases, air) leaves much to be desired. In this case, no one can guarantee that one day, as a result of an accident on the line (for example, if under its weight tipped shaky support), the bare neutral wire is not connected to the vehicle phase. As a result, zero otgorit from the transformer, and we get a lethal voltages, "walk" on the case of home appliances.
AlexeyL (User FORUMHOUSE):
For the circuit TN-C-S, you must either be completely confident in the safety and reliability of coming to you on the street conductor PEN, or the need to ensure the safety of their own ground. In a typical state of local air networks can be confident only in reverse: in the unreliability of PEN. And the construction of the ground, able to withstand the current zero set of neutral neighbors at breakage and misalignment of the big loads on phases - a very difficult and not cheap to do.
Explain: PEN - is combined working null (N) and the protective zero (PE) conductor connecting the transformer substation with the opening flap home.
Using the SIP cable as part of the feed line, of course, it gives some guarantee of security, but the poor condition of ground supports all these safeguards can be put in doubt. Simply put, to create ground-type TN-C-S system is possible only with complete confidence in the reliability of transmission line feed.
As for drawbacks such as the TT system: the system representation of the type require that the presence of the ground circuit protective devices or RCDs diffavtomatov that should be regularly checked for serviceability. At the same time to ensure the safe operation of the CT must be fitted with a potential equalization and artificial grounding circuit, the creation of which takes time, effort and certain costs.
In practice, the establishment of a system TN-C-S always looks more advantageous, but questionable state current supply lines (supply line formed nonisolated conductors, observed her frequent breaks, air bearings are in poor condition, and so on. d.) as a more reliable alternative is recommended to create TT system.
Brief system TN-S
If the house is brought system TN-S, the lead-in plate may be fitted with a grounding bus which should be connected introductory grounding conductor and protective conductor PE, reaching a home consumers. PE conductor can be connected to the re-earthing circuit. To a question about how to do this, we'll be back.
AlexPetrow (User FORUMHOUSE):
In TN-S comes to consumer pyatiprovodka with individual PE and N. nothing should be divided in such a system.
It is the division of the incoming neutral wire, which is supplied to the consumer in TN-C systems and divides the setup of TN-C-S. Such a division is shown in the diagram.
Construction system TN-C-S
If your home is suitable TN-C system, if you have made sure in perfect condition and made sure the feed line, that in the lead-conductor cable used SIP, you can create the type of earthing system TN-C-S.
Separation on the protective conductor PE conductor (having a yellow-green color) and at zero (a blue color) produced in the opening panel.
The shield is connected to the re-grounding system.
In accordance with the updated rules edited SEP PEN conductor separation should be performed prior to induction of protective switchgear apparatus and to the meter. Thus strictly prohibited include protective and switching devices in a circuit PEN and PE conductors. Can only break the circuit conductor N (RB 1.7.145)
AlexPetrow (User FORUMHOUSE):
PEN conductor and PE - are inseparable! All switching devices (auth. switches, circuit breakers, batchfile metering devices, and so on. n.) should be on the line conductor N (its "tear" can be, and sometimes necessary).
Separation conductor PEN is produced by the following scheme:
For the separation use two tires main grounding (GZSH) and null (N). Main grounding bus is connected to an additional earthing circuit through the body panel, while it also connects the opening PEN cable and connect the ground terminal sockets installed in house. N connected to the bus: electrometer, breakers and power terminals domestic power points.
The main bus earthing bar becomes PE after jumper connecting GZSH and N. It is to the PE connection is made and the supplementary ground circuit protective conductors leading to the grounding terminal sockets.
More clearly the division shown in the photo.
In accordance with SAE regulations main ground bus recommended made of copper. It is allowed use of steel tires and tire installation is strictly prohibited aluminum. Typically, GZSH tire and N are made of the same material.
stanislav-e88a (User FORUMHOUSE):
Zero (N) c separating the tire is at the 2-pole automatic introduction, then - at the counter. From the counter zero - to consumers. Dual machines are not necessary (except for the opening). PEN is to be split before. With phase is simple: go to the opening machine, then on the counter, then by consumer groups.
Basic requirements for the node separation conductor PEN are as follows:
- Zero dividing bus N is compulsorily set to the insulator, i.e. it must be isolated from body panel to which is further connected bus PE (because after separation of the two tires do not have nowhere contact);
- All conductors, suitable for separating the tire should be attached via strong bolting that provides the connection and the disconnection of individual conductors;
- GZSH-section must be greater than or equal to the section of the supply conductor PEN.
As protective conductor PE recommended to use special wires. If PE conductors and the phase conductors are made of the same material, the dependence of the minimum cross section of the PE phase section to the next.
Sign «£» in this case stands for - «≤».
If protective and supply conductors are made of different materials, the cross section of PE should be equivalent in its conduction phase section, considered in the table.
The minimum combined cross section of the conductor in the TN-C system must meet the following values: 10 mm² - copper conductors and 16 mm² - for aluminum. If the conductor cross-section is smaller, it is forbidden to share! In this case, one should resort to the creation of the CT system.
Repeated grounding and protective device in the TN-C-S systems
If you wish to protect themselves and their family from the destruction of leakage currents, the system grounding TN-C-S should be equipped with devices (RCD) or differential machines. In accordance with the recommendations of SAE-date edition (izd.7) type TN system, equipped with Device (RCD) to be connected to the re-ground, which is mounted on the entering the house.
SB3 (User FORUMHOUSE):
In particular, it requires repeated execution earthing at the ends of branches and VL are longer than 200 m, as well as the inputs to electric overhead line, in which a protective measure against electric shock is performed protective auto power off indirect contact.
If the RCD in your system is not used, and within 200 m of your panel is already re-grounding, then create an additional ground on the introduction of a special need to house no.
Crazy Cat (User FORUMHOUSE):
If a distance of 200 meters from the I already have repeated grounding, or entry made cables laid in the ground - in the repeated grounding is not necessary.
With regard to the RCD: for additional protection against leakage currents indirect contact to the exposed surfaces electrical supply in general scheme is recommended to implement the device (RCD) or Differential automatic. This protection is triggered weak leakage current cutting off the main power (leakage currents, despite its small size, can be dangerous to humans). Their installation is suitable for the reason that conventional circuit breakers are triggered only on a short-circuit currents.
In modern systems made to install an RCD of two different denominations: general RCD fire, triggered by the current Leakage - 100 mA, and also one (or more) RCD connected to line sockets and triggered on the current - 30mA or 10 mA.
RCD connected to the household appliances, interacting directly with water (.. Washing machines, dishwashers, water heaters, etc.) should be triggered to leakage current - 10mA. On the line of lighting systems RCDs are usually not installed.
As a result, we have just such a scheme.
Re-ground connection body includes an introductory panel to the grounding circuit.
In accordance with the rules of the SAE (para 1.7.102) in alternating voltage up to 1 kV as a grounding circuit for re systems TN-C-S can be used underground structures electric pylons, metal water pipes, grounding and lightning protection circuits t. d. These elements should be used first. If this is not possible, it creates an artificial circuit.
In DC networks grounding wires should be connected to an artificial grounding circuit, which must not be connected with underground pipelines.
On the question of the construction of artificial grounding loop we'll be back.
The cross section of the conductors connecting the plate and the grounding circuit in networks with neutral to earth and with a voltage up to 1 kV, must comply with the following parameters.
If aluminum wire is used, its area should be at least 16 mm².
potential equalization system
After creating a grounding system, equipped with automatic shut-off devices in the house there is a protective conductor connecting all the elements of the power supply system. This conductor is a potential threat. After all, in case of damage of any user on the case of undamaged electrical imposed dangerous potential. He will be there until tripping RCDs, creating danger in direct contact. In order to reduce this voltage must create building equipotential system (EMS) able to equalize the potential of all its conductive parts (building structures, utilities and t. d.).
ASZyuzin1950 (User FORUMHOUSE):
potential equalization system is not an independent measure of protection, but its presence using an automatic power-off is mandatory.
PAF is a kind of grid conductors (PE) combining together all of the conductive elements through GZSH object, i.e. through its portion of the PE. PE bus connection and conductive parts of the building is made radially (separate conductor is supplied to each PE grounding structure). In details construction of the basic (PAF) and further (PAF) equipotential system you can find in the corresponding section FORUMHOUSE.
TT earthing system
If you have come to the conclusion that the danger of inappropriate or connect the system TN-C-S to your home, the only alternative capable of supporting its own security, will create a system TT. Its scheme is as follows.
As you can see, GZSH and grounding wires are connected to nowhere introductory PEN-conductor and the neutral conductor - N.
Use of an RCD or differential automata as a part of the CT system is a prerequisite for its safe operation. Performance characteristics of safety devices in the system to match the RCD systems TN-C-S.
Also in CT systems must be created basic system equipotential (OSUP). Ideally OSUP created complete with an additional system (PRSPs).
If the CT system is connected to the metal shield, all conductors in the panel must be double insulated. Alternatively, the metal shield can be used plastic shields.
AlexPetrow (User FORUMHOUSE):
The metal shield is grounded. The shield does double insulation and take precautions against direct and indirect contact (eg, zero bus will be in the insulating box). If the plastic visor - even better (there are for the street).
For a more reliable insulation in places they pass through the body of the metal shield, you can use special textolite sleeve.
GZSH using copper wire is connected to the conductor, leading to artificial earthing circuit. In the panel to the ground bus wires are fed PE coming from home users and by the equipotential bonding systems.
Underground elements connecting with the shield grounding circuit, it is advisable to make steel (e.g., strips). The use of bare aluminum conductors, in this case forbidden.
Calculation and creating a grounding loop
As is known, dangerous potential developed in the protective conductor PE in the breakdown voltage of the phase on the housing of the household appliance is sent to the least resistance. And to ensure that during the human touch to the open voltage of the power plant continued go in the ground, protecting people from electrical shock, the grounding circuit must have a low resistance. Therefore, the calculation of the grounding circuit reduces to determining the value of the spreading resistance in the ground currents device. This figure depends on several factors:
- From the square grounding elements.
- The distance between them.
- The depth of their immersion into the ground.
- From soil conductivity.
For TT earthing systems installed in networks with voltage up to 1 kV and equipped with RCD protection devices, the rules of the SAE (paragraph 1.7.59) set the following relationship: RaIa <50 V. Where:
- Ia - RCD minimum current setpoint (in our case it is equal to 10 or 30 mA);
- Ra - the total resistance of all elements of the earth system.
In accordance with the formula for the RCD to the setpoint 30A, this figure should not exceed - 1660 ohm (minimum requirement for the CT system). Such values are governed by the rules of the SAE, can be misleading. Therefore, in practice, many people tend to get a ground loop resistance does not exceed 4 ohms (that meets the requirements, extending to the ground power supply circuit).
As a general rule, in order to meet the minimum of resistance to earth loops in the ground is enough to drive one metallic area or pin length -. 2.5... 2 m In practice, in order to ensure more reliable protection uses several protective rods (often - 3) of said length.
bonus (User FORUMHOUSE)
At a distance of 90 cm from the tape base and parallel to it with a sledgehammer scored three earthing. Depth - 2.8 m, the distance between them - 3,5m.
Here is an example of successful protection consisting of a grounding rod.
man (User FORUMHOUSE)
I was able to drive the 6 electrodes of 1.5 m at one point, but I helped Makita taken for this business work. Driven at 0.2 m below the zero level. grounding resistance pacing, but the practice of using such electrode as a grounding shows that the electrode gives a length of 9-10 m on our substrata less than 4 ohms.
If you doubt the number and length of the electrodes, in order to calculate the best grounding loop refer to specialists. Also, these parameters can be found in neighboring countries having a valid ground loop, allowed supervisors to operate after appropriate resistance measurements.
With regard to the minimum cross-section of the vertical dimensions of the electrodes: they can be taken out of the familiar table.
The electrodes in practice often used smooth steel bars with a diameter of at least 16 mm or pointed corners (50-50). Strapping electrodes used steel strip size 4x40 or 5x40.
BORIS LOC (User FORUMHOUSE):
I performed the ground, scoring three 3-meter valves (d16mm). Soil - moist-tight plastic clay. Then united by welding steel grounding bus 4x40 mm.
Positioning the electrodes as possible in a row, and at the corners of geometric shapes (e.g., at the corners of the triangle). In each case, their location is determined by the convenience of the assembling process and the presence of free space.
The distance between the electrodes is determined by the coefficient of use of the rod which is equal to - 2.2. That is, for the system to work at maximum efficiency, the distance between two identical electrodes must be not less than 2.2 the length of each of them (in all directions). When reducing this distance (in practice so often the case) system efficiency will drop.
Before beginning installation removed topsoil, and then, in the marked points, clogged electrodes.
The upper ends of the electrodes are strapped strip or steel rod and are joined by welding.
At the final stage circuit is connected to the grounding electrical shield.
All compounds grounding circuit design must be made by welding.
For those who want to learn more practical experience in the field of construction ground home systems, On our portal there is a theme dedicated to this issue. For information on how to make grounding system installation and that what materials it should be usedYou can learn on the basis of practical experience FORUMHOUSE users. The video - how to create a system of power supply and other utilities in the country-frame house.