Grounding in a private house: calculation, device, installation

Recommendation points

• Fundamentals of protective grounding
• Calculation of the grounding device
• Grounding installation
• Materials and tools for the grounding device
• Assembling the grounding device

The article describes how to independently make grounding in a private cottage. We will understand the principles of grounding, learn how to calculate the configuration of this device, and determine what materials are needed.

Some 20-25 years ago, we were building private and public buildings, without even thinking about the effective protection of a person from electric shock. Recently, everything has become different – our input distribution boards are becoming larger, they now house dozens of circuit breakers, several RCDs, and there is almost always a separate grounding bus there. What changed? Electricity is now literally around us, houses have a huge number of wiring accessories, a lot of household appliances and power units, which are potential sources of danger, in addition, we probably began to value human life more.

Modern building codes (in particular, PUE) require that at least one of the following measures be applied to protect a person in residential premises:

• voltage drop;
• potential equalization;
• use of double insulation of wires;
• use of isolation transformers;
• installation of residual current devices;
• arrangement of grounding, grounding.

Of course, the issue of security should be approached comprehensively and used in all possible ways, but grounding in the house must be mandatory.

Grounding electrical installations is the most reliable and effective method of protection, which, together with other measures, makes household electricity absolutely safe. In fact, grounding is a deliberate connection of the enclosures of electrical installations (elements that are not energized) with the ground. For many homeowners, the organization of grounding seems to be either too expensive and technologically advanced, or too simple, which is also not entirely true..

In a private house, it is not technically difficult to make reliable grounding, since the distance to the ground is very small, and you can always find free areas in the yard. Residents of old apartment buildings are much less fortunate, where the grounding loops no longer work, and then some compatriots manage to individually ground themselves from the upper floors, laying a conductor from their apartment along the walls of the building to the very ground. Meanwhile, it would be a mistake to believe that any iron pin driven into the soil, or any water pipe, will become a normal working ground loop. Grounding is a system consisting of several important elements with specific rated parameters, which functions according to certain principles, closely interacts with other systems.

Fundamentals of protective grounding

In a faulty electrical device (for example, if the insulation of the supply wire is damaged), voltage may appear on its case. When a person touches the device, the current rushes into the ground, passing through his body and often causing irreparable harm, not all protective devices can react or have time to quickly break the circuit. Why does the current go to the ground? Because it easily accepts a discharge, since it has a very high electrical capacity. If the leakage current (through conduction current flowing between two or more electrodes) is offered another, simpler way, for example, a conductor with a lower resistance – for grounding it should not exceed 4 ohms, then it will go to the ground along it, and not through a person with body resistance 1 kOhm. A current leak occurs in the circuit, and a residual current device (RCD) in a split second disconnects the damaged area.

That is why all modern electrical actuators and units are designed in such a way that a grounding conductor can be connected to them, and three-core wires are used for wiring. This also applies to all modern household appliances, where the body and one of the contacts of the power plug are connected – they use sockets with a PE contact (antennae) to power them. All lamps, chandeliers, sconces have terminals for connecting “yellow” wiring, and metal boxes of distribution boards and metal structures on which the power equipment is located are grounded. All consumers of networks with an alternating current voltage over 42 V are grounded without fail, for direct current – over 110 V. Note that grounding provides not only the electrical safety of people, but also:

• stabilizes the operation of electrical installations;
• protects devices from overvoltage;
• reduces the amount of network interference and the intensity of high frequency electromagnetic radiation.

The grounding device consists of the following elements:

• earthing switch
• grounding conductors

The grounding conductor will be any part of the grounding device that connects electrical installations to the grounding electrode, these are separate wire cores (generally accepted – in yellow insulation), elements of the external and internal circuits, a special bus located in the shield.

A grounding conductor is an electrode, the part of the grounding circuit that is in direct contact with ground. This element ensures the flow of currents into the ground and their dispersion. Depending on whether buried elements of building structures are used for this or a specially created conductor, natural and artificial grounding conductors stand out. According to the PUE, preference should always be given to the use of natural ground electrodes (clause 1.7.35), in a private house it can be:

• well metal casing;
• any steel pipelines, including pipes for laying electrical wires;
• lead armor of the power cable;
• various metal posts and supports on the street, for example, fence elements;
• buried reinforced concrete and metal elements of the building (columns, trusses, mines, foundations).

Artificial electrodes can be used if the resistance of natural ground electrodes does not correspond to the norm, then we will consider them in more detail.

Calculation of the grounding device

The main parameter that needs to be calculated is the conductivity of the ground electrode. In other words, we need to choose an electrode of such a configuration so that the resistance of the grounding device does not exceed the standard. The provisions of the PUE indicate the following numbers, which are the permissible maximum:

• 2 Ohm – for a single-phase line voltage of 380 volts;
• 4 ohms – for 220 volts;
• 8 ohms – for 127 volts.

With a three-phase current, the maximum resistances will be the same 2, 4 and 8 ohms, but only for voltages of 660, 380 and 127 volts, respectively.

What determines the conductivity of the ground electrode system (read, the resistance of the grounding device)? Simplified – from the area of ​​contact of the electrode with the ground and soil resistivity. The larger the ground electrode, the lower the resistance, the more current the soil takes. All calculation formulas suggest taking into account the surface area of ​​the electrode and the depth of its immersion. For example, to calculate a single circular-section grounding device, we have the following formula:

Where: d – pin diameter, L – electrode length, T – distance from the surface to the middle of the ground electrode, ln – logarithm, ? – constant (3.14), ? – soil resistivity (Ohm m).

Please note that soil resistivity is the main calculation parameter. The lower this resistance, the more conductive our grounding will be and the more effective protection. The main basic figures for a certain type of soil can be found in publicly available tables and graphs, but much depends on its actual state – density, water balance, temperature, seasonal frost depth, presence and concentration of “electroactive” chemicals in it – alkalis, acids, salts … Moreover, at different depths, the situation can change significantly, the physical properties of the continental foundation become different, aquifers appear, which reduce resistance, the temperature increases … As a rule, with increasing depth, the soil becomes more current pick-up.

At temperatures below zero, the resistance of soils increases sharply due to the freezing of water. Therefore, there are certain difficulties with grounding in areas with permafrost soils. For the same reason, the length of the ground electrodes should be an order of magnitude greater than the seasonal depth of freezing in normal latitudes..

Ideally, the resistance of the ground and the grounding device as a whole should be investigated practically, while the formulas will help us make the basic calculations. Often, the analysis takes place directly at the stage of assembling the circuits – the electrodes are immersed and measurements of the grounding conductivity are made in real time: if the resistance is too high, then the number of ground electrodes or the degree of their burial is increased.

Note that grounding must work at any time of the year, therefore it is recommended to check it in the most unfavorable conditions (drought, frost). If this is not possible, special coefficients are applied to the results, taking into account seasonal changes in soil resistance in a particular area..

If several electrodes are used to equip the ground electrode, then the calculation procedure will be somewhat different:

1. Resistance is calculated for each of them (the formula above can be applied).
2. Indicators are summed up.
3. It is necessary to take into account the “utilization factor”.
4. The formula looks like this:

Where: N – number of ground electrodes, TO_and – utilization rate, R₁ resistance of each electrode separately.

As you can see, the conductivity of the horizontal elements connecting the electrodes into a single circuit is not taken into account..

The utilization factor can cause some complexity – it reflects the phenomenon in which adjacent electrodes in the circuit influence each other, since the zones of dissipation of currents in the soil begin to intersect when too close. The closer the individual ground electrodes are to each other, the greater the total resistance of the grounding device. A working sphere with a radius equal to its length is formed around each electrode in the ground, which means that the ideal distance between the ground electrodes will be their length in the ground (L), multiplied by 2.

The ratio of the distance between the electrodes to their length	Number of electrodes	Coef. use
1	five	0.7
1	ten	0.6
1	15	0.53
1	20	0.5
2	five	0.81
2	ten	0.75
2	15	0.7
2	20	0.67

Closed loop placement
The ratio of the distance between the electrodes to their length	Number of electrodes	Coef. use
1	five	0.65
1	ten	0.55
1	15	0.51
1	20	0.45
2	five	0.75
2	ten	0.69
2	15	0.66
2	20	0.63

To calculate how many ground electrodes need to be buried in the ground, use the following formula:

Where: R – design resistance of the grounding device, R₁ – resistance of one electrode, TO_and – utilization rate.

As for the arrangement of grounding electrodes, they do not have to form a triangle, although this is the most common configuration of the circuit. The electrodes can be placed in one row with a series connection. This option is convenient if a narrow strip of land is allocated for arranging grounding..

Grounding installation

In principle, two types of grounding devices can be distinguished, which differ from each other in terms of installation technique and material characteristics. The first is a pin modular design (factory-made) with one or more electrodes, the second is a home-made version with several ground electrodes from rolled metal. Their main differences are only in the organization of the buried part – conductive, “upper”, their part is identical.

Factory grounding kits are technologically advanced and have a number of advantages:

• supplied as a complete set, elements are specially designed for the arrangement of protection and are produced on industrial equipment;
• almost do not require excavation, no welding work is needed;
• allow you to go deep to several tens of meters and get a very low, stable resistance of the entire device.

The only drawback of such systems is their high cost..

Materials and tools for the grounding device

Artificial grounding conductors should be made of steel rolled metal. Suitable for these purposes:

• corner;
• round or rectangular pipe;
• rod.

To protect the metal from corrosion, galvanized electrodes are used. It is also allowed to use electrically conductive concrete as a ground electrode.

In the factory sets, these are one and a half meter solid-drawn copper-plated pins with threads at the ends. A sharp conical tip is installed on the first element, the individual pins are connected by means of threaded brass couplings. The electrodes are immersed in the ground using hand-held percussion tools (SDS-Max cartridge, impact power approx. 20 J). An adapter and a guide head are used to transfer energy from the rock drill. The connection between the grounding conductor and the electrode is made through a stainless steel clamp. To protect the joints from corrosion and reduce the resistance at the joints, a special paste is used.

Attention! Earthing switches must not be painted, lubricated or preserved in any other way that would reduce their conductivity..

The effect of corrosion (the steel part is gradually thinning) should be taken into account when choosing the cross-section of the electrode, it is selected with a certain margin, which ensures sufficient durability of the circuit. The minimum permissible cross-sections of ground electrodes located in soils are limited by regulatory documents:

• galvanized rod – 6 mm;
• ferrous metal rod – 10 mm;
• rolled rectangular section – 48 mm².

Attention! The thickness of the shelves of rectangular steel or the wall thickness of the pipes must be at least 4 mm.

A strip is most often used as a conductor connecting several electrodes in the ground, but a wire, corner, pipe can be used. With these materials, it is possible to bring grounding to the electrical panel itself (the cross-section of materials has fewer restrictions: rod – 5 mm, rectangular steel – 24 mm², wall and shelf thickness – 2.5 mm).

The grounding conductor inside the building must have a cross-sectional area equal to the cross-section of the phase conductor used in the house wiring.

There are also minimum requirements:

• uninsulated aluminum – 6 mm;
• copper uninsulated – 4 mm;
• aluminum in insulation – 2.5 mm;
• copper in insulation – 1.5 mm.

For commutation of all grounding conductors it is necessary to use grounding bars made of electrotechnical bronze. In the TT grounding system, these elements of the switchboard are mounted directly on the wall of the metal box.

The self-made ground electrode is deepened with a sledgehammer, factory kits are hammered in with jackhammers. In both cases, we recommend preparing a platform or a ladder. To work with black rolled products, it will be necessary to use manual arc welding.

Assembling the grounding device

Let’s consider the order of actions. At the initial points, we will indicate the operations typical for the installation of both types of grounding electrodes.

Layout and excavation.It is recommended to install earthing switches in the ground at a distance of about one meter from the foundation. In accordance with the project, the circuit is marked – as we have already said, it can be an equilateral triangle, line, circle, several rows … The distance between the electrodes is taken from 1.2 meters, making it more than twice the length of the ground electrode system is meaningless. As a basic option, suitable for most of our conditions, you can take a triangle with a side of 1.5-3 meters and a length of electrodes of 2-3 meters.

Next, you need to dig a trench with a depth of about 70-80 cm, the minimum depth that is allowed is 50 cm. The width of the trench at the deepening points should provide convenience for welding conductors, usually they dig with slopes about 0.5-0.7 meters wide.

To drive a modular single-electrode grounding, only one pit 50x50x50 cm in size is required.

Preparing the electrode.To facilitate the immersion of the ground electrode into the ground, the rolled metal is sharpened with the help of a grinder, for example, shelves are cut at an angle at an angle, the pipe is cut obliquely, the rod is sharpened. If used metal is used, then, if necessary, it should be completely cleaned of protective coatings.

A pointed head is screwed onto the factory modular ground pin, the connection is coated with paste.

The corners (most often they are 50x50x5 mm corners) are hammered into the ground by blows.It is most convenient to start work from the scaffold. If the metal is soft, it is better to hit the workpieces through wooden spacers. The head of the earthing switch should rise 150-200 mm above the bottom of the trench so that we can connect the electrodes into a circuit.

The factory pins are buried using a demolition hammer with an SDS-Max shank chuck and an impact capacity of 20-25 joules. After immersion of each pin (1.5 meters), a sleeve and the next earthing element are screwed onto it, this cycle is repeated until the electrode reaches the design depth, or a failure occurs (impossibility of further deepening). In case of failure, additional grounding pins are clogged, the system becomes multi-electrode.

Earthing switches are connected with a horizontal conductor,it is generally most convenient to work with a 40×4 mm strip. For ferrous metal, welding is necessary here, since the bolted joints will quickly oxidize and the resistance of the device will increase. Tacking will not work – you need a high-quality long weld.

From the resulting contour, take the strip towards the house, bend it and fix it on the plinth. At the end of the strip we weld an M8 bolt through which a protective grounding conductor coming from the shield will be connected.

A clamp clamp is installed on the last modular pin and the conductor is fixed. The clamp is wrapped with a special waterproofing tape.

The trench is covered with soil.It is recommended to use dense homogeneous fine-grained compositions for these purposes..

Factory sets with one electrode can be completed with a plastic revision well.

The grounding conductor is led into the switchboard.It can be attached directly to the building structures, with the exception of areas with high humidity – it is better to use insulators there. Through the walls, the conductor is drawn by means of metal or plastic pipes-sleeves, in fact, the laying rules apply the same as for the “main” wiring (this will be one of the following articles).

In the switchboard, the conductor, after being crimped with a bolt connection, is connected to the ground bus, which is installed on the box body (TT system).

The resistance of the grounding device is checked with a multimeter, if, taking into account seasonal factors (determined by the State Energy Supervision Service for different latitudes, there are ready-made tables) it exceeds 4 Ohm, then it is necessary to increase the number of electrodes.

During switching of the switchgear, the conductors of wires in yellow insulation (they come from current consumers) are also clamped in the bus connectors.

When connecting sockets, devices, lamps, the yellow grounding conductors are switched at the appropriate places (usually they are marked with a special sign – three horizontal stripes of different sizes), for example, in sockets this is a central screw.

A system in which the ground loop is not connected in any way with the neutral working conductor N is called TT. It is recommended for use when the TN options (there is a connection between the neutral and the grounding conductor) cannot be used, for example, if the condition of the overhead power supply lines is unsatisfactory. Of course, for this common reason, it has become very popular. But, it should be noted that the TT system with an independent solid-grounded neutral of consumers must be insured with the help of an RCD. We will talk about residual current devices in the next article..