Overview earth resistance measurement methods

Grounding is used in the implementation of various electrical systems projects. The very concept of "ground" is seen schematically connecting the electrical circuit to the ground potential portion.

ground loop comprises a conductor and the electrode are embedded deep in the ground. Traditional electrical action in practice is to measure the ground resistance only More already launched and operated networks. We'll show you how, and how it is made important action.

Which requires the measurement?

Brilliant solution following tasks perfect zero resistance is achieved in the grounding circuit:

1. Prevent the occurrence of stress on the body of technological machines.
2. To achieve effective reference potential electrical equipment.
3. Eliminate static currents.

True Electro Experience shows: the result of a perfect zero can not be obtained.

In any case, the grounding electrode produces a no resistance.

The specific resistance value is determined by:

• resistance of the electrode at the contact point with the conductive bus;
• the contact area between the earth electrode and the ground;
• the soil structure, giving different resistance.

Practice ground loop resistance measurement notes that the first two factors can be neglected, but subject to logical conditions:

1. The ground electrode is made of metal with high conductivity.
2. pin electrode body thoroughly cleaned and firmly planted in the ground.

There remains a third factor - resistive ground surface. He sees the main part of the estimated ground loop resistance measurement.

Calculated, thanks to the following formula:

R = pL / A,

wherein: p - soil resistivity, L - conditional penetration, A - the working area.

Overview of measuring methods

There are several options for measuring resistance ground loop, Each of which quite accurately to determine the required amount.

3-point detection system

For example, a technique often used three-point circuit, based on the potential drop effect.

Measurements carried out in three main steps:

1. Measure the voltage on the electrode E1 and E2 probe.
2. Measurement of current at electrode E1 and E3 probe.
3. Calculation (formula R = E / I) the resistance of the grounding electrode.

For this technique, the accuracy of measurements is logically dependent on the place of installation of the probe E3. It is recommended to introduce into the ground at a distance - optimally beyond the so-called field ESE (effective electrode resistance) A1 and A2.

Measurement technology "62%"

If the soil structure for placing the ground electrode differs homogeneous content, method of "62%" to determine the resistivity of ground loops promises good performance.

The method is applicable only to a circuit ground electrode. The accuracy of location is due to the possibility of working on a straight section of the probes with respect to the ground electrode.

control probes installation point

A simplified two-point method

Application of this method requires the measurement of another grounding quality beyond that will be subjected to study. The technique is relevant to densely populated areas, where it is often not possible to operate with widely supporting the working electrodes.

two-point measuring method is characterized in that at the same time shows the result for two of grounding devices in series. This explains the requirements for the high quality of execution of the second ground, so as not to take into account the resistance.

To perform the computations also measured impedance grounding rail. The result is deducted from the overall measurement results.

The accuracy of this method is poor in comparison with the two preceding. Here, an important role played by the distance between the ground electrode whose resistance is measured and a second ground. As standard, this technique is not applicable. It's kind of an alternative when you can not use other methods of measurement.

Accurate measurements of the four points

For most embodiments of resistance measurement most optimal way, in addition to 2-D and 3-point, we are considered a 4-point technique. Such measurements are endowed with technology devices like 4500 series tester. Judging from the name of the method, at the work site in a line and at equal distances are placed four working electrode.

instrument current generator is connected to the extreme electrodes, whereby a current flows between them whose value is known. On the other two terminals of the device internal working electrode are connected.

On these terminals present a voltage drop value. The final result of measurements - resistance value (in Ohms), the value of which device shows on the display.

Devices in a series of 4500 is often used to measure touch voltage. Device using a special module is generated in the ground voltage low value - an imitation of the cable.

At the same time on the scale of the device indicates the current flowing through the grounding circuit. Indications on the screen taken as a basis and multiplied by the estimated current value of the land. In this manner, calculating touch voltage.

For example, the maximum expected current in the area of ​​damage is equal to 4000A. On the screen of the device indicated value 0.100. Then the value of the contact voltage is equal to 400V (4000 * 0.100).

S.A6415 measurement device (6410, 6412, 6415)

The uniqueness of this method - the possibility of carrying out measurements without disconnecting the earthing circuit. Also here should allocate preferential direction, when measuring the total resistance of the grounding device is allowed by the inclusion in the grounding circuit of the resistive component of the compounds.

The principle of operation similar to the following:

1. Special transformer current is created in the circuit.
2. Current flows in the loop formed.
3. the measured signal is detected by a synchronous detector.
4. The resulting signal is converted by the ADC.
5. The result is displayed on the LCD display.

The device is equipped with a module (selective amplifier), by which the desired signal efficiently cleared from all sorts of noise - N.Ch. and wp noise. Mites legs articulated in their excited state formed contour surrounding the grounding conductor.

instrument measurement instruction S.A6415

The procedure for the operator S.A6415 series lucidly described in the instructions supplied with this unique device.

For example, there is a need to measure the ground resistance of an electrical module (transformer Electric, etc.).

Sequencing:

1. Open access to the grounding bus by removing the protective casing.
2. Grab tongs conductor (bus electrode or directly) grounding.
3. Select measurement mode "A" (current measurement).

The maximum value of the device current is 30A, however in the case of exceeding this number can not perform the measurement. It is necessary to remove the device and attempt to repeat the measurement at another point.

When received on the scale of the current value is placed in the acceptable range, you can continue switching the instrument to measure resistance "?".

Flashed on the display will show the result of the total value of resistance, including:

• electrode and the ground bus;
• neutral contact with an earthing electrode;
• compounds on contact between the neutral line and the ground electrode.

Working with the tongs, it should be borne in mind: inflated readings of earth resistance is usually caused by poor contact with the ground of the earth electrode.

Also, the reason of high resistance may be ragged busbar tire. High numbers resistances at points of connections (splices) conductors may also affect the readings.

General guidelines for the measurement of USG

Before construct a ground circuitFor example for a gas boiler, it is necessary to obtain accurate information about the area in which the soil will be laid the ground electrode. Often, to determine the values ​​of "p" are invited to contact the soil to existing tables.

However, this option allows tables purely indicative data. Therefore, relying on them is not necessary. The true values ​​soil resistance may vary significantly.

Option # 1: single-layer soil

If the soil has a uniform component, its resistivity is measured procedure "test electrodes".

The method involves performing a specific procedure in two stages:

1. Take control rod probe length of a little more depth to the design tab.
2. Immerse the probe into the ground vertically to the depth of the design tab.
3. The remaining above the ground end is used to measure the spreading resistance (Rr).
4. USG determined from the formula p = Rr * Ψ.

It is desirable to perform the process several times at different points of the work platform. Alternative measurements help to achieve accurate earth resistance measurements.

Option # 2: multi-layer soil

For such a situation, measurement is performed by stepwise USG sensing. That is, the control probe is immersed to a depth of working steps and at a position of each stage are performed resistivity measurements. Calculating an average USG made using formulas for each individual measurement.

Then, based on the climatic characteristics of the area, find the values ​​for seasonal changes. In this manner (rather complex) obtained calculated values ​​USG upper layers. The underlying layers are considered as not subject to seasonal changes and because the calculation for them is limited to a few simplistic measurements and calculations.

Requirements for execution of works

Operation of such a plan, of course, carried out by qualified personnel, representing the specialized organizations. So, for the operation of security guards in residential buildings, as a rule, meet the public service. Make any measurements at these points are allowed only by recourse to these services.

Electrical circuits are dangerous systems. Despite the fact that the communication household sector are calculated at least 1000V voltage, this voltage is deadly to humans. Required to comply with all necessary safety precautions when handling electrical equipment. Layman often these measures are simply unknown.

With the features of the ground facilities for a bath in a city apartment acquaint next articleWhich contains rules and guidelines for the conduct of work.

Conclusions and useful videos on the topic

Performing measurements in practice with the device:

The execution of works related to test ground resistance is required necessary, regardless of the complexity of circuitry categories and the facility where installed, or installed and operated electrical equipment. Many specialized organizations are willing to provide such services.

Leave, please comment in the box located below. It is possible that you know the simple and effective way to measure the ground loop resistance, are not given in the article. Ask questions, share useful information and pictures.