This article discusses earthing of low voltage electrical installations from the point of view of IEC 60364
 Apart from electrical installations, earthing finds importance with electronic or instrumentation and IT due to the usage of VLSI ICs and their associated failures or problems. Because of its application related with safety, it is analysed in various International and National standards related to specific context.
This article approaches earthing from the view point of IEC 60364-5-54-Ed 3.The scope of this standard is limited to earthing arrangement and protective conductors including protective bonding conductors of low voltage installations i.e. 1,000 V AC or 1,500 V DC in order to satisfy the safety of electrical installations with cross reference from below standards. IEC 60364-5-54 does not cover EMC which is covered by IEC 61000-5-2: EMC – installation and mitigation guidelines – earthing and cabling.
IEC 60364-4-41: 2005: LV electrical installations – protection for safety- protection against electric shockIEC 60364-4-44: 2007: LV electrical installations – protection for safety- protection against voltage and electromagnetic disturbances.IEC 60364-5-51:2005: Electrical installation of buildings – selection and erection of electrical equipment -common rules.IEC 61140: 2001: Protection against electric shock – common aspects for installation and equipment.IEC 62305- 2010 (Ed. 2): All four parts.
Relevant acronymsT- Direct connection of a point with earth (T- Terra in Latin)I – Connection of a point with earth via high impedance (I- Isolated)N- Direct connection to neutral at the origin of installation which is connected to earth. TN is further classified into TN- S (separate)/TN-C (combined) and TN-C-S (combined at source and separate at load).Earthing is intended to provide connection to earth which:

Is reliable and suitable for the protection of the installation.
Can carry earth fault I and protective conductor I to earth, without danger from thermal, thermo-mechanical and electro-mechanical stresses and from electric shock arising from these I.
If relevant, is also suitable for functional requirement.
Suitable for the foreseeable external influences (IEC 60364-5-51) – e.g. mechanical stresses and corrosion.
Where I with HF are expected to flow (cl 444 of IEC 60364-4-44: 2007).
Protection against electric shock shall not be adversely affected by any foreseeable change of earth electrode resistance (example: corrosion, drying, freezing etc.)
Type, dimension and material of earth electrode shall be selected to withstand corrosion and to have adequate mechanical strength for the intended life time.
Main parameters for corrosion: Soil pH at the site, soil resistivity, soil moisture, stray and leakage AC and DC I, chemical contamination and proximity of dissimilar metals.
Minimum thickness of protective coating is greater for vertical earth electrode because of greater exposure to mechanical stresses while being embedded than for horizontal earth electrode. Efficiency of earth electrode depends on its configuration and local soil conditions. Depending upon the value of earth resistance required one or more earth electrodes suitable for the soil conditions shall be selected.
Types of earth electrodes
Concrete embedded foundation earth electrode
Soil embedded foundation earth electrode
Metallic electrode embedded directly in soil- vertically or horizontally (eg. rods, wires, tapes, pipes, plates).
Metal sheath of cables (according to local conditions)
Other suitable underground metal work (eg. metal water pipes) according to local conditions.
Welded metal reinforcement of concrete (except pre-stressed concrete) embedded in the earth.
Dos and Don’tsEarth electrode shall not be directly immersed in water of a stream, river, pond or lake. Earth electrode parts shall be connected together by exothermic welding, pressure connectors, clamps or other suitable mechanical connectors. The same is applicable for connection of earthing conductor to an earth electrode. Cross sectional area of earthing conductors shall be 6 sq.mm. for Cu or 50 sq.mm. for steel. Where lightning protection system is connected to earth electrode, cross sectional area of earth conductor should be 16 sq.mm. for Cu and 50 sq.mm. for steel.  Aluminium shall not be used as earthing conductor.
Where more than one earthing terminal is provided, they shall be interconnected. It shall be possible to individually disconnect each earth conductor connected to the MET. Disconnection shall be possible only by means of a tool. A protective conductor not forming part of a cable shall be mechanically protected if installed in conduit/trunking.
For equipotential bonding MET shall be provided and the following shall be connected to it.

Protective bonding conductors
Earthing conductors
Protective conductors

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This article discusses earthing of low voltage electrical installations from the point of view of IEC 60364
 Apart from electrical installations, earthing finds importance with electronic or instrumentation and IT due to the usage of VLSI ICs and their associated failures or problems. Because of its application related with safety, it is analysed in various International and National standards related to specific context.
This article approaches earthing from the view point of IEC 60364-5-54-Ed 3.The scope of this standard is limited to earthing arrangement and protective conductors including protective bonding conductors of low voltage installations i.e. 1,000 V AC or 1,500 V DC in order to satisfy the safety of electrical installations with cross reference from below standards. IEC 60364-5-54 does not cover EMC which is covered by IEC 61000-5-2: EMC – installation and mitigation guidelines – earthing and cabling.
IEC 60364-4-41: 2005: LV electrical installations – protection for safety- protection against electric shockIEC 60364-4-44: 2007: LV electrical installations – protection for safety- protection against voltage and electromagnetic disturbances.IEC 60364-5-51:2005: Electrical installation of buildings – selection and erection of electrical equipment -common rules.IEC 61140: 2001: Protection against electric shock – common aspects for installation and equipment.IEC 62305- 2010 (Ed. 2): All four parts.
Relevant acronymsT- Direct connection of a point with earth (T- Terra in Latin)I – Connection of a point with earth via high impedance (I- Isolated)N- Direct connection to neutral at the origin of installation which is connected to earth. TN is further classified into TN- S (separate)/TN-C (combined) and TN-C-S (combined at source and separate at load).Earthing is intended to provide connection to earth which:

Is reliable and suitable for the protection of the installation.
Can carry earth fault I and protective conductor I to earth, without danger from thermal, thermo-mechanical and electro-mechanical stresses and from electric shock arising from these I.
If relevant, is also suitable for functional requirement.
Suitable for the foreseeable external influences (IEC 60364-5-51) – e.g. mechanical stresses and corrosion.
Where I with HF are expected to flow (cl 444 of IEC 60364-4-44: 2007).
Protection against electric shock shall not be adversely affected by any foreseeable change of earth electrode resistance (example: corrosion, drying, freezing etc.)
Type, dimension and material of earth electrode shall be selected to withstand corrosion and to have adequate mechanical strength for the intended life time.
Main parameters for corrosion: Soil pH at the site, soil resistivity, soil moisture, stray and leakage AC and DC I, chemical contamination and proximity of dissimilar metals.
Minimum thickness of protective coating is greater for vertical earth electrode because of greater exposure to mechanical stresses while being embedded than for horizontal earth electrode. Efficiency of earth electrode depends on its configuration and local soil conditions. Depending upon the value of earth resistance required one or more earth electrodes suitable for the soil conditions shall be selected.
Types of earth electrodes
Concrete embedded foundation earth electrode
Soil embedded foundation earth electrode
Metallic electrode embedded directly in soil- vertically or horizontally (eg. rods, wires, tapes, pipes, plates).
Metal sheath of cables (according to local conditions)
Other suitable underground metal work (eg. metal water pipes) according to local conditions.
Welded metal reinforcement of concrete (except pre-stressed concrete) embedded in the earth.
Dos and Don’tsEarth electrode shall not be directly immersed in water of a stream, river, pond or lake. Earth electrode parts shall be connected together by exothermic welding, pressure connectors, clamps or other suitable mechanical connectors. The same is applicable for connection of earthing conductor to an earth electrode. Cross sectional area of earthing conductors shall be 6 sq.mm. for Cu or 50 sq.mm. for steel. Where lightning protection system is connected to earth electrode, cross sectional area of earth conductor should be 16 sq.mm. for Cu and 50 sq.mm. for steel.  Aluminium shall not be used as earthing conductor.
Where more than one earthing terminal is provided, they shall be interconnected. It shall be possible to individually disconnect each earth conductor connected to the MET. Disconnection shall be possible only by means of a tool. A protective conductor not forming part of a cable shall be mechanically protected if installed in conduit/trunking.
For equipotential bonding MET shall be provided and the following shall be connected to it.

Protective bonding conductors
Earthing conductors
Protective conductors

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