CHAPTER 6

EARTHING SYSTEM

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• Three earthing systems such as defined in IEC 364 are:

1) exposed-conductive parts connected to neutral TN;

2) earthed neutral TT;

3) unearthed (or impedance-earthed) neutral IT

EARTHING SYSTEM

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PURPOSE OF EARTHING SYSTEM

• regards protection of persons and property: mastery of insulation fault effects.

• They are considered to be equivalent with respect to safety of persons against indirect contacts

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CLASSISFICATIONS

• The extent of the earth fault and the consequences deriving from the touching of live exposed-conductive-parts are specifically related to the neutral condition of the power system and to the types of system earthing.

• As a consequence, to select the proper device for the protection against earth faults, it is necessary to know the installation distribution system. The International Standard IEC 60364-3 classifies the electrical systems with the combination of two letters.

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CLASSISFICATIONS

• The first letter indicates the relationship of the power system to earth:

>> T = direct connection to earth of one point, usually the neutral, in ac systems

>> I = all live parts isolated from earth or one point, usually the neutral, connected to earth through an impedance.

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CLASSISFICATIONS

• The second letter indicates the relationship of the exposed-conductive- parts of the installation to earth:

>> T = direct electrical connection of exposed-conductive parts to earth

>> N = direct electrical connection of the exposed-conductive parts to the earthed point of the power system.

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CLASSISFICATIONS

• Subsequent letters, if any, indicates the arrangement of neutral and protective conductors:

S = neutral and protective functions provided by separate conductors

C = neutral and protective functions combined in a single conductor (PEN conductor).

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CLASSISFICATIONS

• For TN-S, TN-C-S and TT systems the following explanations should aid a full understanding of the earthing arrangements and their scope of application.

• The nomenclature of these system types is as follows:

• T =Earth (from the French word Terre)

• N=Neutral

• S=Separate

• C=Combined

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TT SYSTEMS

• This arrangement covers installations not provided with an earth terminal by the Electricity Supply Company.

• Thus it is the method employed by most (usually rural) installations fed by an overhead supply.

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TT SYSTEMS

• Neutral and earth (protective) conductors must be kept quite separate throughout the installation, with the final earth terminal connected to an earth electrode by means of an earthing conductor.

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• The earth fault current returns to the power supply node through the soil.

• In this type of electrical installations the neutral is usually distributed and its function is making the phase voltage (e.g. 240 V) available for the supply of the single-phase loads of civil installations.

• Effective earth connection is sometimes difficult.

• Because of this, socket outlet circuits must be protected by a residual current device (RCD) with an operating current of 30 mA.

TT SYSTEMS

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• Effective earth connection is sometimes difficult.

• Because of this, socket outlet circuits must be protected by a residual current device (RCD) with an operating current of 30 mA.

TT SYSTEMS

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TT SYSTEMS

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TN SYSTEMS

• In TN systems, the neutral is directly earthed, whereas the exposed-conductive-parts are connected to the same earthing arrangement of the neutral.

• TN electrical systems can be divided into three types based on the fact that the neutral and protective conductors are separate or not:

1) TN-S

2) TN-C

3) TN-C-S

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TN SYSTEMS: TN-S• The neutral conductor N and the protective

conductor PE are separated

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TN SYSTEMS: TN-S

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TN SYSTEMS: TN-C

• TN-C: the neutral and protective functions are combined into a single conductor, called PEN.

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TN SYSTEMS: TN-C-S

• TN-C-S: the neutral and protective functions are partially combined into a single PEN conductor and partially separated PE + N

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TN SYSTEMS: TN-C-S

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TN SYSTEMS

• In TN systems the earth fault current returns to the power supply node through a direct metal connection (PE or PEN conductor) without

practically affecting the earth electrode

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IT SYSTEMS

• The installation arrangements in the IT system are the same for those of the TT system.

• However, the supply earthing is totally different. • The IT system can have an unearthed supply, or one

which is not solidly earthed but is connected to earth through a current limiting impedance.

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IT SYSTEMS

• The total lack of earth in some cases, or the introduction of current limiting into the earth path, means that the usual methods of protection will not be effective.

• For this reason, IT systems are not allowed in the public supply system.

• An exception is in medical situations such as hospitals. Here it is recommended that an IT system is used for circuits supplying medical equipment that is intended to be used for life-support of patients.

• The method is also sometimes used where a supply for special purposes is taken from a private generator.

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• The earth fault current returns to the power supply node through the earthing arrangement of the exposed conductive parts and the capacities to earth of the line conductors.

IT SYSTEMS

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• Let’s say Taman Jejawi, in Kangar Town, There is a terrace house has two master bed room including a small drawing room and total load consumption of the house is 450 watts.

• Can you draw the grounding system for this house?• Can you estimate the length of copper conductors?• Can you estimate the number of copper connectors?• Can you calculate grounding resistance for this house?• Can you estimate the budget ?

Example Grounding System

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•Try yourself

Drawing of Grounding System

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•Try yourself

Grounding Resistance Calculation

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•Try yourself

Budget of Grounding System

THANK YOU

Terima Kasih