# Why is double earthing necessary for 3-phase machines and equipment?

Table of content

• 3:60 min

• 19 Aug 2024

## Why Earthing Important?

The main purpose of the earthing of electrical equipment is to avoid the danger of getting electric shock. The proper earthing also provides fire protection. The large current flowing through the undefined high resistance path may increase the chance of fire due to heat, and also it can cause electric shock or electrocution due to rise in voltage between  the undefined path with respect to ground.

The metallic enclosure of the electrical appliance must be earthed to provide low resistance path to leakage current in order to protect the human being from getting electrocution and also to protect the electrical system.

When any live conductor in the enclosure touches to the body of metallic enclosure, it attains the live potential. If anyone touches the enclosure it may electrocute. To avoid this untoward incident, the body of the enclosure is earthed.

The earth has very low resistance, and thus the current starts flowing from the enclosure body to earth. The earth fault current trips the protection relay and thus the power supply is cut off. One earthing point is sufficient to provide earth fault protection, then why the metallic enclosure of the electrical equipment should be earthed from two distinct point of the enclosure.

## Why Double Earthing?

The electrical equipment enclosure earthed at two separate points with two separate earth pits provides the following advantages.
• When the electrical equipment enclosure is earthed at two points on the enclosure body, it establishes the two  current path at the time of attaining of live potential. In the case of discontinuity of one circuit, the earth current keep on flowing through the other circuit and thus, the equipment remains fully protected against the earth fault.
• The two points earthing provides two parallel path for earth fault current. The two parallel path is connected to two separate earth points. Thus the equivalent resistance of the two parallel path gets reduced and it offers low resistance path to the fault current. If the resistance of one path is 0.4 ohms and the other path is 0.3 ohms, the equivalent resistance of the two parallel path is [(0.4 x 0.3)/(0.4+0.3)]=0.17 ohms. Thus the effective path resistance of the two parallel circuit gets reduced and it provides better reliable protection.

To summarize,  the electrical equipment is earthed at two distinct points for the following reasons.

• The earthing remains intact in case of broken of one of the earthing points.
• To have very low earthing resistance.

## FAQ

### Why is earthing required for equipment?

Earthing provides a path for electrical current to flow safely to the ground in the event of a system fault or overload, reducing the risk of fire, electrocution and damage to equipment. In addition, effective earthing ensures that the voltage in the system is stable and remains within safe limits

### Why do we use two types of earthing on transformers?

Why do we have two types of earthing on a transformer? – Quora. One type is safety earthing – bonding the non-current carrying metal parts in the transformer to earth – tank, radiators, core etc. The second is neutral earthing. This is relevant only if the transformer has Star connected winding

### What does double grounded mean?

Double Grounded Neutral problems occur on the RCD when the neutral conductor is grounded for a second time. The live and neutral wires pass through the current transformer in the RCD and if that neutral conductor is grounded for a second time after the CT we suddenly have a DGN condition

### Why are there two earth terminals?

Anonymous user. All new double socket outlets have 2 earth terminals so that if the circuit is wired in a ring the earth connections can go separately

### What is the IEC standard for earthing?

International standard IEC 60364 distinguishes three families of earthing arrangements, using the two-letter codes TN, TT, and IT. The first letter indicates the connection between earth and the power-supply equipment (generator or transformer)

### What is the purpose of multiple grounding?

A multipoint ground is an alternate type of electrical installation that attempts to solve the ground loop and mains hum problem by creating many alternate paths for electrical energy to find its way back to ground

### Why is double earthing used?

Double earthing system is used for earthing of power equipment. Explanation: According to Section-90 of IE Rules, two earthing must be provided to power equipment because: If there is one earth circuit and the current path gets broken then the enclosed body or equipment may attain live potential

### What happens if transformer neutral is not grounded?

Because when there is a phase deviation, if the neutral line is not grounded, the phenomenon of “neutral point drift” will appear, that is, the neutral line is charged, and sometimes the voltage will be very high, which will cause electric shock hazards

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