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How to calculate the ground - domestic cases, necessary for effective protection device

How to make ground settlement

Question grounding of household electrical appliancesthe majority of the inhabitants seems secondary and optional, since not so long ago in the wiring of houses are not even provided for the laying of the ground wire. In our time, the number of household appliances in a household increased significantly, increased their energy consumption, thus increased load on the grid. Ignore the obvious would be the height of irresponsibility, so the electrical current requirements govern the rules under which protective ground is required for all appliances with capacity of 1.3 kW. Thus, even if the ground is not provided initially, it should be to settle on their own, that, first of all, provides for the calculation of grounding. Anyone who has faced a similar problem is important to understand what was going on, because if the online payment grounding perform on a computer program, the understanding of the basic principles of electrical engineering, this calculation does not add a simple user. Responsibility for the life and health of their loved ones the user will no doubt be useful information below. It will help to establish the necessity of arrangement of the ground, which ultimately will help to avoid unpleasant and dangerous moments during operation of electrical appliances in the home. Consider the necessary calculation formulas, we try to understand the specifics of the issue in detail.

Content

  • An example of the work program
  • Calculation of earth resistance
  • Calculation of ground loop

In operation, electrical devices in theirconductive body appears voltage caused by the passage of current in the windings of transformers or motors. Even if the body has no direct connection to the power line, it formed the tension caused by the electromagnetic field of these currents. To avert tension with the body of the appliance, it must be connected to ground, ie ground.

Consider, computer calculation of ground - Elcut example of the work program.

An example of the work program

As you can see, the calculation of ground application performs brilliantly, but we must first deal with the peculiarities of the program.

Consider the technical feasibilityGrounding on the example of modern televisions and power strips. Modern TVs have an emergency-off overvoltage, for his work requires grounding, otherwise the device will not respond to a voltage exceeding the permissible parameters that will cause damage to the expensive device. Surge protectors for connecting computers also require to work effectively grounding the device, otherwise the filter will work as a simple extension cord.

The device requires grounding to work effectively

Mains filter with ground contacts for ground and home appliances

In addition to the need for technical groundthere is a more important task - safe operation of appliances. To illustrate, consider a common situation: the refrigerator is placed next to the battery, the unit is not grounded properly and there was a small body voltage of about 50-100 V, adult touching the body may not even feel any discomfort, but if a body the device touches the child while touching (accidentally or intentionally) to the battery of central heating, it will be between the grounded conductor (battery) and a voltage source (refrigerator) as a result of the electrical circuit closes through the baby's body. Current flow through the body of a child can lead to irreversible consequences, so the device to the protective earth must be treated very seriously.

The modern high-rise buildings the execution groundnot be easy. Wiring in these homes already includes a ground wire laid parallel to the power line. For safe operation of electrical appliances will be enough to install and properly connect the three-pin socket.

Mains outlet

A three-outlet, earthing contacts are indicated by arrows

In those homes where Outlet circuit ground was not provided in the construction, ityou can do personally, if a guard with counters located at the entrance to the staircase. This panel ground wire or a zero (depending on the power scheme house - four or five-wire) connected to the metal body panel, a free terminal on the housing must be found to connect to it. This rule must be observed - each ground wire should be connected to individual screw.

But arrange thus grounding orvanishing in the old "Khrushchev" unlikely to succeed, the use of the working of the neutral conductor for the purpose of zeroing is prohibited, this requires a separate earthing. As a natural grounding conductive structures can be used in direct contact with the ground, and specially designed device, referred to as artificial grounding. Natural grounding include: reinforcement of the foundation, water pipes (except for heating), the outer metal shell armored cables (except aluminum). Artificial grounding devices are vertical and horizontal. That is done in a driven into the ground metal cores interconnected by a conductive strip welding method, or in the form of metal electrodes laid in the ground horizontally, below the frost line.

Calculation of earth resistance

For effective earthing device is necessarymake a preliminary assessment, the main numerical parameter of the grounding circuit is its resistance, the current rules of electrical devices regulate its value is not more than 8 ohms in a network with a voltage of 220 V and 4 ohms at a voltage of 380 V. These parameters loop impedance must be observed at all times of the year. Naturally, when a lower voltage is allowed a greater resistance value as ground task is to ensure the safety of people in contact with the body in the event of electrical contact with him phase voltage.

With less resistance to ground on the device would be a smaller part of the electric potential. Measurement of resistance earthing is performed by special gauges.

The device, which measures the earth resistance

Earth Ground Testers

Calculation of ground loop

Calculation of ground loop It is based on measurements of the specificsoil resistance, a characteristic which determines the level of electrical conductivity of the earth. The specific resistance of the soil depends on its density, chemical and mechanical composition, temperature and humidity. From this it is clear that this figure will be significantly different under different weather conditions and at different times of the year, so for the calculations are taken most seasonal indicators resistivity.

The resistance of the soil

The resistivity of soils

Calculation of resistance of a single vertical grounding by the formula:

Where:

R₁ - calculated resistance of a single rod (Ohm)

Π - constant (3.141592)

ρ - soil resistivity (Ohm • m)

L - length of the earthing rod (m)

ln - the natural logarithm

T - the distance from the middle of the rod to the ground (m)

d - diameter of the rod (m)

For the calculation of the earthing resistance consists of several identical rods and at the same depth are using the following formula:

grounding resistance calculation

Where:

R - calculated earthing resistance consists of several rods

R₁ - resistance of a single rod (Ohm)

K₁ - coefficient of the mutual influence of electrodes

N - number of rods in earthing

The coefficient depends on the mutual influence of electrodesthe distance between the electrodes, remember that it should not be less than their length. The optimal distance equal to the length of the rods 2,2. Connecting rods in multiple electrode earthing produce metal strip 150 mm2.

As seen from the above formulas, the generalearthing resistance depends on the soil resistivity and electrode length t. e. the greater the electrical resistance of the soil, the longer must be in earthing electrodes. If the nature of the soil does not allow to drive a long electrodes, they must be used in larger quantities and in highly rocky rocks, may have to apply a horizontal or electrolytic grounding

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