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

By Admin | Garden And Buildings / Communication
26 April 2016

Question ground Household Electrical majority of inhabitants seem secondary and optional, as not so long ago in the wiring of houses do not even involves laying the ground wire.In our time, the number of household electrical appliances in the household has increased considerably increased their energy consumption, thus increased load on the grid.Ignore the obvious would be the height of irresponsibility was so modern electrical safety requirements govern the rules according to which the protective ground is required for all household electrical capacity of more than 1.3 kW.Thus, even if the ground is not provided initially, it should be to settle on their own, that, first of all, for the calculation of the ground.Anyone who has faced a similar problem, it is important to understand what was going on, because if the calculation of the grounding line will execute the program on the computer, the understanding of the basic principles of electrical engineering simple user, this calculation has not increased

.Responsible for the life and health of their loved ones the user will no doubt be useful Underwritten information.It will help to establish the necessity of arrangement of the ground, which ultimately will 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

During operation of electrical devices on their conductive casing voltage appears due to the passage of current through the windings of transformers or motors.Even if the body does not have a direct connection to the power line, it forms 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 - an example of the program Elcut.

Example program ↑

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

consider the technical feasibility of the ground on the example of modern televisions and power strips.Modern TVs have the emergency shutdown overvoltage, for his work requires grounding, otherwise the device will not respond to the excess of the permissible voltage parameters that will cause damage to expensive devices.Surge protectors to connect computers is also required for efficient operation of the device ground, otherwise the filter will work as a simple extension cord.

The device is to be grounded to work effectively
Surge with voltage and ground for household appliances

addition to the technical need to ground there is a more important problem - the safe operation of appliances.To illustrate, consider a common situation: a fridge is next to the battery, the unit is not grounded properly, and the housing having a little stress about 50-100 V, an adult touching the body, maybe even not feel any discomfort, but if to the bodydevice touches a 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 body of the child.Current flow through the body of a child can lead to irreversible consequences, so the device protective earth must be treated very seriously.

In modern high-rise buildings grounding not 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 sufficient to properly install and connect the three-pin socket.

Socket with grounding contacts
three-prong outlet, arrows indicate grounding

In homes where grounding chain outlets was not provided during construction, it can be done personally, if the flap with counters located at the entrance to the stairwell.This panel ground wire or a zero (depending on the power scheme house - four or five-wire) connected to the metal body panel, to connect to it is necessary to find a free terminal on the housing.This rule must be observed - each ground wire should be connected to individual screw.

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

calculation grounding resistance ↑

An efficient grounding necessary to make a preliminary assessment, the main numerical parameter grounding circuit is its resistance, the current rules for Electrical regulate its value is not more than 8 ohms 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 greater resistance value as the task of grounding is safety of people in contact with the body in the event of electrical contact with a phase voltage.

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

The device, which measures the earth resistance
earth resistance meter

Calculation of ground loop ↑

ground loop calculation is based on measurements of soil resistivity, a characteristic which determines the level of electrical conductivity of the ground.The resistivity of the soil depends on its density, mechanical and chemical 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 the calculations are taken most seasonal performance resistivity.

Earth resistance
soil resistivity

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

where:

R₁ - calculated resistance of a single rod (ohms)

Π - constant (3,141592)

ρ- soil resistivity (Ohm ∙ m)

L - length of the rod earth electrode (m)

ln - natural logarithm

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

d - diameter of the shaft (m)

To calculate the resistance of the earthing consisting of multiple identical cores and are at the same depth, use the following formula:

calculation of earthing resistance

where:

R - calculated resistance of the earthing consisting of several rods

R₁ - resistance of a single rod (ohms)

K₁ -coefficient of mutual influence of the electrodes

N - the number of rods in earthing

factor mutual influence of the electrodes depends on the 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 a multi-electrode earthing produce metal strip 150 mm2.

As can be seen from the above formula, the total resistance of the earth depends on soil resistivity and the length of the electrodes, ie. E. The greater the electrical resistance of the soil, the longer should be in earthing electrodes.If the nature of the soil does not allow to drive long electrodes, they must be used in larger quantities and in a very rocky rocks, may have to apply a horizontal or electrolytic grounding