What is the purpose of earth resistance test?
The purpose of this test is to detect and locate high resistance joints, which are a typical result of corrosion in exposed conductor systems.
What is the purpose of earth electrode?
Earth electrodes are designed to be installed in a building and improve the grounding system. They are driven into the soil below ground level, furthermore, are made of conductors that will not corrode easily. Earthing systems are extremely important and act as a sort of insulation protecting from electrical hazards.
What is earth electrode resistance test?
Earth electrode resistance – the resistance of an earth electrode to Earth. In a TT system where a connection to earth is not provided by the supply authority it is still necessary for an LV final circuit protective device to disconnect an earth fault within 0.2 s.
What is the difference between earth resistance and earth electrode resistance?
Definition: The resistance offered by the earth electrode to the flow of current into the ground is known as the earth resistance or resistance to earth. The earth resistance mainly implies the resistance between the electrode and the point of zero potential.
How do you test the earth electrode resistance?
An alternating current (I) is passed through the outer electrode C and the voltage is measured, by means of an inner electrode P, at some intermediary point between them. The Earth Resistance is simply calculated using Ohm’s Law: Rg = V/I.
What are the main factors on which the resistance of an earthing system depends?
It is the resistance of the soil to the passage of electric current. It varies from soil to soil. It depends on the physical composition of the soil, moisture, dissolved salts, grain size and distribution, seasonal variation, current magnitude etc.
What instrument is used for earth electrode test?
Measurement using an earth fault loop impedance tester The earth electrode test is carried out as follows: isolate the electrical installation at the main switch, verify the electrical supply is off using a voltage indicating device with proving unit, lock off and label.
What are the factors affecting earthing resistance?
Factors affecting on Earth resistivity
- Soil Resistivity. It is the resistance of soil to the passage of electric current.
- Soil Condition.
- Dissolved salts.
- Climate Condition.
- Physical Composition.
- Location of Earth Pit.
- Effect of grain size and its distribution.
What is the resistance of earth should be?
Ideally a ground should be of zero ohms resistance. There is not one standard ground resistance threshold that is recognized by all agencies. However, the NFPA and IEEE have recommended a ground resistance value of 5.0 ohms or less.
What is the range of earthing resistance?
Why is earthing resistance kept low?
⎇ A strong current surges through the earth wire because it has a very low resistance. This breaks the fuse and disconnects the appliance.
What is the purpose of an earth electrode test?
The purpose of this test is to establish that the resistance of the soil surrounding an earth electrode is suitable and that the electrode makes contact with the soil Recognised types of earth electrode The following types of earth electrode are recognised: 1. earth rods or pipes
What is earth electrode and earth electrode resistance?
An earth electrode and earth electrode resistance are defined in BS 7671 as: Earth electrode – conductive part, which may be embedded in the soil or in a specific conductive medium, e.g. concrete or coke, in electrical contact with the Earth.
How do you measure the resistance of an electrode?
You can then take the instrument reading as being the resistance of the electrode under test. The dead earth method is the simplest way to make an earth resistance test. With this method, resistance of two electrodes in series is measured — the driven rod and the water system. But there are three important limitations:
When to carry out the earth electrode resistance test?
It is recommended that the earth electrode resistance test is carried out when the ground conditions are least favorable, such as during dry weather. Note: If the reading of the three values are above 200 ohms, the soil condition may not be stable, as soil conditions change due to factors such as soil drying and freezing.