How to measure ground resistance with megger

How to measure ground resistance with megger

Ground resistance is a very important parameter in the electrical system, which is directly related to the safe operation of the equipment and personal safety. A common tool for measuring ground resistance is a megger (also called a megohmmeter or ground resistance tester). This article will introduce in detail how to use a megger to measure ground resistance, and provide relevant data and analysis.

1. Principle of measuring ground resistance with megometer

The megger injects a certain current into the grounding device and measures the voltage drop between the grounding device and the earth, thereby calculating the grounding resistance value. The basic principle is Ohm's law: R=U/I, where R is the ground resistance, U is the voltage drop, and I is the injected current.

2. Steps for measuring ground resistance with megometer

1.Preparation: Make sure the grounding device under test is disconnected from the electrical system to avoid interference.

2.Connect test leads: Connect the E terminal (ground terminal) of the megger to the grounding device under test, and connect the P terminal (potential terminal) and C terminal (current terminal) to the auxiliary ground electrode respectively.

3.shake handle: Shake the handle at 120 rpm to maintain a stable speed.

4.Read data: After the pointer is stable, read the ground resistance value displayed on the megometer.

5.Record results: Record the measurement results and compare them with the standard values to determine whether the grounding resistance is qualified.

3. Standard value of ground resistance

Different electrical systems have different requirements for ground resistance. The following are the standard values of ground resistance for common electrical systems:

4. Factors affecting ground resistance measurement

1.soil resistivity: The higher the soil resistivity, the greater the ground resistance.

2.Length and number of ground electrodes: The longer and more the grounding poles are, the smaller the grounding resistance is.

3.Burial depth of ground electrode: The deeper the burial depth, the smaller the grounding resistance.

4.ambient humidity: The higher the humidity, the better the conductivity of the soil and the smaller the grounding resistance.

5. Common problems and solutions

1.Measurement value is unstable: It may be that the speed of shaking the handle is uneven or the test line is in poor contact. It needs to be checked and re-measured.

2.Measured value too large: It may be that the ground electrode is corroded or the soil is dry. The ground electrode needs to be replaced or the soil needs to be watered to moisten it.

3.No response from the shaker: It may be that the battery power is low or the test line is disconnected. The battery needs to be replaced or the circuit needs to be checked.

6. Precautions for using the megohmmeter

1.Safety first: Make sure the electrical system is powered off before measurement to avoid the risk of electric shock.

2.Regular calibration: The megometer needs to be calibrated regularly to ensure measurement accuracy.

3.Avoid humid conditions: The megohmmeter should be avoided being used in humid environments to prevent damage.

4.Store correctly: Clean after use and store in a dry place.

7. Summary

The megometer is an important tool for measuring ground resistance. Proper use of the megometer can effectively evaluate the safety of the grounding system. Through the introduction of this article, I believe you have mastered the methods and precautions for measuring ground resistance with a megger. In actual operation, be sure to strictly follow the steps to ensure the accuracy and safety of the measurement results.