Measurement of resistance of the ground loop

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Measurement of resistance of the ground loop

Grounding is the electrical connection of an electrical appliance to the ground.

It is necessary to protect a person from electric shock in the event of a malfunction or damage to the appliance.

In the role of a grounding rod the usual metal rod is most often used, but a complex of a special form consisting of complex elements can also be used.

To check the quality of grounding, measure the resistance of the ground loop.

Contents:

  • Operating principle
  • Measuring procedure
  • Earthing resistance measurement method
  • Service prices

Principle of operation

This measurement measures the value of the electrical ground resistance, which can be reduced if necessary, increasing the conductivity of the medium or the contact area.

To do this, increase the amount of salts in the ground, use a lot of metal rods or use some other methods.

The grounding device and grounding requirements are governed by the rules for electrical devices and installations.

It should be noted that simple grounding only reduces the phase voltage that has been applied to the body of the appliance.

For a reliable protection of human life and health, it is desirable to install a grounding device in conjunction with a protective shutdown device.

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The grounding device is selected and designed individually for each individual case.

The resistance of the ground loop is measured immediately after the commissioning of the residential facility or enterprise.

Further measurements are carried out once a year.

The structure and parameters of the earthing device depend on several factors: composition and type of soil, soil moisture, etc. Before you install the ground, make up the project.

The resistance of the earthing device is measured by special devices that allow the specific value of earth resistance, grounding rod and its elements to be determined accurately and quickly.

The resistance of the grounding device can be measured in four-, three- and two-pole methods. For multiple measurements, the kit includes special pliers.

Resistance measurement instruments can take into account various parameters that can influence the measurement process and correct the results.

Measurement procedure

The measurement procedure itself is carried out as follows: an artificial circuit of an electric current is closed through the earthing device and a voltage drop measurement is performed on it.

An auxiliary electrode is placed next to the test ground rod, which is connected to the same source of electrical voltage.

The voltage drop on the first rod is then measured by a probe. Measurements are made in the zone of zero potential.

This method of measuring grounding quality is most often used.

Earthing resistance measurement method

The earth resistance must be measured in summer or winter, when the ground resistance takes a greater value.

The resistance values ​​of the grounding devices can be different for each individual case, for example, for a private house, the resistance value of the grounding devices is 30 Ohm.

Two, three or four pole ground resistance measurement methods are effectively used for measurements.

When carrying out resistance measurements, it is necessary to follow the appropriate instructions:

  • a potential probe for resistance measurement is placed on the control section between the grounding electrode and the current auxiliary probe;
  • the distance from the main earth electrode to the current auxiliary probe is five times the depth of the grounding rod or the length of the strip electrode;
  • , when measuring the resistance of the grounding system complex, this distance is calculated depending on the greater length of the diagonal that passes between the individual earthing devices.

In some cases, additional earth resistance measurement may be required. For example, resistance measurements are carried out in a variety of underground communications.

In this case, several measurements are made for different distances and directions of the beams between the probes. The worst result is considered to be the real value.

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The resistance of the earthing device at any time of the year should not exceed the permissible value of the value.

With all the maximum permissible values, it is possible to get acquainted with the help of Annex 3( PTEEP) or Table 1.8.3( PUE-7).

In addition to measuring the resistance of earthing devices, insulation resistance measurements should also be made.

Such measurements will show the state of the insulation of electrical circuits and electrical equipment.

Methods for measuring insulation resistance, as well as standards for testing and checking insulation of electrical appliances are determined by the PUE, PTEEP, GOST, etc.

Insulation resistance is measured by a special instrument - a megger.

This device consists of a continuous current generator with a manual drive, additional resistors and a magnetoelectric logometer.

Before starting the measurement, check that there is no voltage on the test object. The insulation is thoroughly cleaned from dirt and dust, after which the object is grounded for 2-3 minutes. This is necessary to remove residual charges.

To the device or line to be tested, the megohmmeter is connected by means of separate wires with insulation having a greater resistance, usually not less than 100 MΩ.

Insulation resistance measurements are made with a stable position of the instrument needle. To do this, rotate the generator knob quickly and evenly.

The exact insulation resistance is determined from the reading of the megger. At the end of the measurements, the test object must be discharged.

Service prices

Insulation and grounding resistance measurements can be ordered from specialized companies or electrical laboratories.

It is not recommended to perform such measurements independently, as this is very dangerous.

The cost of measuring the resistance of the ground loop and insulation depends on the complexity of the work, as well as the range of the object( travel expenses).

The filling of the measurement report and the technical report is included in the cost of the tests. Therefore, it is not necessary to pay for them separately.

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