Earthing System

Introduction

In an electrical installation an earthing system or grounding system connects specific parts of that
installation with the Earth's conductive surface for safety and functional purposes. The point of reference
is the Earth's conductive surface. The choice of earthing system can affect the safety and
electromagnetic compatibility of the installation.

Regulations for earthing systems vary considerably among countries, though many follow the
recommendations of the International Electrotechnical Commission. Regulations may identify special
cases for earthing in mines, in patient care areas, or in hazardous areas of industrial plants.

In addition to electric power systems, other systems may require grounding for safety or function. Tall
structures may have lightning rods as part of a system to protect them from lightning strikes. Telegraph
lines may use the Earth as one conductor of a circuit, saving the cost of installation of a return wire over
a long circuit. Radio antennas may require particular grounding for operation, as well as to control static
electricity and provide lightning protection.

Protective earthing

An earth ground connection of the exposed conductive parts of electrical equipment helps protect from
electric shock by keeping the exposed conductive surface of connected devices close to earth potential,
when a failure of electrical insulation occurs. When a fault occurs, current flows from the power system
to earth. The current may be high enough to operate the over current protection fuse or circuit breaker,
which will then interrupt the circuit. To ensure the voltage on exposed surfaces is not too high, the
impedance (resistance) of the connection to earth must be kept low relative to the normal circuit
impedance.

An alternative to protective earthing of exposed surfaces is a design with "double insulation" or other
precautions, such that a single failure or highly probable combination of failures cannot result in contact
between live circuits and the surface. For example, a hand-held power tool might have an extra system
of electrical insulation between internal components and the case of the tool, so that even if the
insulation for the motor or switch fails, the tool case is not energized.
Functional earthing
A functional earth connection serves a purpose other than electrical safety, and may carry current as part
of normal operation. For example, in a single-wire earth return power distribution system, the earth
forms one conductor of the circuit and carries all the load current. Other examples of devices that use
functional earth connections include surge suppressors and electromagnetic interference filters.

Low-voltage systems

In low-voltage networks, which distribute the electric power to the widest class of end users, the main
concern for design of earthing systems is safety of consumers who use the electric appliances and their
protection against electric shocks. The earthing system, in combination with protective devices such as
fuses and residual current devices, must ultimately ensure that a person must not come into touch with a
metallic object whose potential relative to the person's potential exceeds a "safe" threshold, typically set
at about 50 V.

On electricity networks with a system voltage of 240 V to 1.1 kV, which are mostly used in industrial /
mining equipment / machines rather than publicly accessible networks, the earthing system design is as
equally important from safety point of view as for domestic users.

In most developed countries, 220 V, 230 V, or 240 V sockets with earthed contacts were introduced
either just before or soon after World War II, though with considerable national variation in popularity.
In the United States and Canada, 120 V power outlets installed before the mid-1960s generally did not
include a ground (earth) pin. In the developing world, local wiring practice may not provide a
connection to an earthing pin of an outlet.

For a time, US National Electrical Code allowed certain major appliances permanently connected to the
supply to use the supply neutral wire as the equipment enclosure connection to ground. This was not
permitted for plug-in equipment as the neutral and energized conductor could easily be accidentally
exchanged, creating a severe hazard. If the neutral was interrupted, the equipment enclosure would no
longer be connected to ground. Normal imbalances in a split phase distribution system could create
objectionable neutral to ground voltages.

Recent editions of the NEC no longer permit this practice. For these reasons, most countries have now
mandated dedicated protective earth connections that are now almost universal. If the fault path between
accidentally energized objects and the supply connection has low impedance, the fault current will be so
large that the circuit overcurrent protection device (fuse or circuit breaker) will open to clear the ground
fault. Where the earthing system does not provide a low-impedance metallic conductor between
equipment enclosures and supply return (such as in a TT separately earthed system), fault currents are
smaller, and will not necessarily operate the overcurrent protection device. In such case a residual
current detector is installed to detect the current leaking to ground and interrupt the circuit.

IEC terminology

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):

"T" — Direct connection of a point with earth (Latin: terra)

"I" — No point is connected with earth (isolation), except perhaps via a high impedance.

The second letter indicates the connection between earth or network and the electrical device being
supplied:

"T" — Earth connection is by a local direct connection to earth (Latin: terra), usually via a ground rod.

"N" — Earth connection is supplied by the electricity supply Network, either as a separate protective
earth (PE) conductor or combined with the neutral conductor.

Types of TN networks

In a TN earthing system, one of the points in the generator or transformer is connected with earth,
usually the star point in a three-phase system. The body of the electrical device is connected with earth
via this earth connection at the transformer. This arrangement is a current standard for residential and
industrial electric systems particularly in Europe.[2]

The conductor that connects the exposed metallic parts of the consumer's electrical installation is called
protective earth (PE; see also: Ground). The conductor that connects to the star point in a three-phase
system, or that carries the return current in a single-phase system, is called neutral (N). Three variants of
TN systems are distinguished:
TN−S
PE and N are separate conductors that are connected together only near the power source.
TN−C
A combined PEN conductor fulfils the functions of both a PE and an N conductor. (on 230/400v
systems normally only used for distribution networks)
TN−C−S
Part of the system uses a combined PEN conductor, which is at some point split up into separate
PE and N lines. The combined PEN conductor typically occurs between the substation and the
entry point into the building, and earth and neutral are separated in the service head. In the UK,
this system is also known as protective multiple earthing (PME), because of the practice of
connecting the combined neutral-and-earth conductor via the shortest practicable route to a local
Earth-Rod at the source and at each premises, to provide both System Earthing and Equipment
Earthing at each of these locations.[3] [4]. Similar systems in Australia and New Zealand are
designated as multiple earthed neutral (MEN) and, in North America, as multi-grounded neutral
(MGN).

TN-S: separate protective earth (PE) and neutral (N) conductors from transformer to consuming device, which are
not connected together at any point after the building distribution point.
TN-C: combined PE and N conductor all the way from the transformer to the consuming device.

TN-C-S earthing system: combined PEN conductor from transformer to building distribution point, but separate
PE and N conductors in fixed indoor wiring and flexible power cords.

It is possible to have both TN-S and TN-C-S supplies taken from the same transformer. For example, the
sheaths on some underground cables corrode and stop providing good earth connections, and so homes
where high resistance "bad earths" are found may be converted to TN-C-S. This is only possible on a
network when the neutral is suitably robust against failure, and conversion is not always possible. The
PEN must be suitable reinforced against failure, as an open circuit PEN can impress full phase voltage
on any exposed metal connected to the system earth downstream of the break. The alternative is to
provide a local earth and convert to TT. The main attraction of a TN network is the low impedance earth
path allows easy automatic disconnection (ADS) on a high current circuit in the case of a line-to-PE
short circuit as the same breaker or fuse will operate for either L-N or L-PE faults, and an RCD is not
needed to detect earth faults.
TT network

In a TT (Terra-Terra) earthing system, the protective earth connection for the consumer is provided by a
local earth electrode, (sometimes referred to as the Terra-Firma connection) and there is another
independently installed at the generator. There is no 'earth wire' between the two. The fault loop
impedance is higher, and unless the electrode impedance is very low indeed, a TT installation should
always have an RCD (GFCI) as its first isolator.

The big advantage of the TT earthing system is the reduced conducted interference from other users'
connected equipment. TT has always been preferable for special applications like telecommunication
sites that benefit from the interference-free earthing. Also, TT networks do not pose any serious risks in
the case of a broken neutral. In addition, in locations where power is distributed overhead, earth
conductors are not at risk of becoming live should any overhead distribution conductor be fractured by,
say, a fallen tree or branch.

In pre-RCD era, the TT earthing system was unattractive for general use because of the difficulty of
arranging reliable automatic disconnection (ADS) in the case of a line-to-PE short circuit (in comparison
with TN systems, where the same breaker or fuse will operate for either L-N or L-PE faults). But as
residual current devices mitigate this disadvantage, the TT earthing system has become much more
attractive providing that all AC power circuits are RCD-protected. In some countries (such as the UK) is
recommended for situations where a low impedance equipotential zone is impractical to maintain by
bonding, where there is significant outdoor wiring, such as supplies to mobile homes and some
agricultural settings, or where a high fault current could pose other dangers, such as at fuel depots or
marinas.

The TT earthing system is used throughout Japan, with RCD units in most industrial settings. This can
impose added requirements on variable frequency drives and switched-mode power supplies which often
have substantial filters passing high frequency noise to the ground conductor.
 IT network

In an IT network, the electrical distribution system has no connection to earth at all, or it has only a high
impedance connection.

Comparison

TT IT TN-S TN-C TN-C-S

Earth fault loop

High Highest Low Low Low
impedance

RCD preferred? Yes N/A Optional No Optional

Need earth electrode at

Yes Yes No No Optional
site?

PE conductor cost Low Low Highest Least High

Risk of broken neutral No No High Highest High

Safety Safe Less Safe Safest Least Safe Safe

Electromagnetic
Least Least Low High Low
interference
 High loop impedance Double fault, Broken Broken Broken
Safety risks
(step voltages) overvoltage neutral neutral neutral

Continuity of Safety and

Advantages Safe and reliable Safest Cost
operation, cost cost

Other terminologies

While the national wiring regulations for buildings of many countries follow the IEC 60364
terminology, in North America (United States and Canada), the term "equipment grounding conductor"
refers to equipment grounds and ground wires on branch circuits, and "grounding electrode conductor"
is used for conductors bonding an earth ground rod (or similar) to a service panel. "Grounded conductor"
is the system "neutral". Australian and New Zealand standards use a modified PME earthing system
called Multiple Earthed Neutral (MEN). The neutral is grounded(earthed) at each consumer service
point thereby effectively bringing the neutral potential difference to zero along the whole length of LV
lines. In the UK and some Commonwealth countries, the term "PNE", meaning Phase-Neutral-Earth is
used to indicate that three (or more for non-single-phase connections) conductors are used, i.e., PN-S.

Resistance-Earthed Neutral

A resistance earth system is used for mining in India as per Central Electricity Authority Regulations.
Instead of a solid connection of neutral to earth, a neutral grounding resistor (NGR) is used to limit the
current to ground to less than a750 mA. Due to the fault current restriction it is more safe for gassy
mines. Since the earth leakage is restricted, leakage protection devices can be set to less than 750 mA.
By comparison, in a solidly earthed system, earth fault current can be as much as the available short-
circuit current. The neutral earthing resistor is monitored to detect an interrupted ground connection and
to shut off power if a fault is detected.

Earth Leakage Protection

Earth Leakage of current can be very harmful for human beings, should it pass through them. To avoid
accidental shock by electrical appliances/ equipment earth leakage relay/sensor are utilized at the source
to isolate the power when leakage exceed certain limit. Earth leakage circuit breaker are used for the
purpose. Current sensing breaker are called RCB/ RCCB. In the industrial applications, Earth leakage
relays are used with separate CT(current transformer) called CBCT(core balanced current transformer)
which sense leakage current(zero phase sequence current) of the system through the secondary of the
CBCT and this operates the relay. This protection works in the range of mA and can be set from 30 mA
to 3000 mA.

Earth Connectivity Check

A separate pilot core p is run from distribution/ equipment supply system in addition to earth core. Earth
connectivity check device is fixed at the sourcing end which continuously monitor earth connectivity.
The pilot core p initiate from this check device and runs through connecting trailing cable which
generally supply power to moving mining machinery(LHD). This core p is connected to earth at the
distribution end through a diode circuit, which complete the electric circuit initiated from the check
device. When earth connectivity to vehicle is broken, this pilot core circuit get disconnected, the
protecting device fixed at sourcing end activate and, isolate the power to machine. This type of circuit is
a must for portable heavy electric equipment (like LHD (Load, Haul, Dump machine)) being used in
underground mines.

Properties
Cost

 TN networks save the cost of a low-impedance earth connection at the site of each consumer. Such a
connection (a buried metal structure) is required to provide protective earth in IT and TT systems.
 TN-C networks save the cost of an additional conductor needed for separate N and PE connections.
However, to mitigate the risk of broken neutrals, special cable types and lots of connections to earth are
needed.
 TT networks require proper RCD (Ground fault interrupter) protection.

Safety

 In TN, an insulation fault is very likely to lead to a high short-circuit current that will trigger an over
current circuit-breaker or fuse and disconnect the L conductors. With TT systems, the earth fault loop
impedance can be too high to do this, or too high to do it within the required time, so an RCD (formerly
ELCB) is usually employed. Earlier TT installations may lack this important safety feature, allowing the
CPC (Circuit Protective Conductor or PE) and perhaps associated metallic parts within reach of persons
(exposed-conductive-parts and extraneous-conductive-parts) to become energized for extended periods
under fault conditions, which is a real danger.
 In TN-S and TT systems (and in TN-C-S beyond the point of the split), a residual-current device can be
used for additional protection. In the absence of any insulation fault in the consumer device, the equation
IL1+IL2+IL3+IN = 0 holds, and an RCD can disconnect the supply as soon as this sum reaches a threshold
 (typically 10mA – 500mA). An insulation fault between either L or N and PE will trigger an RCD with
high probability.
 In IT and TN-C networks, residual current devices are far less likely to detect an insulation fault. In a TN-
C system, they would also be very vulnerable to unwanted triggering from contact between earth
conductors of circuits on different RCDs or with real ground, thus making their use impracticable. Also,
RCDs usually isolate the neutral core. Since it is unsafe to do this in a TN-C system, RCDs on TN-C
should be wired to only interrupt the line conductor.
 In single-ended single-phase systems where the Earth and neutral are combined (TN-C, and the part of
TN-C-S systems which uses a combined neutral and earth core), if there is a contact problem in the PEN
conductor, then all parts of the earthing system beyond the break will rise to the potential of the L
conductor. In an unbalanced multi-phase system, the potential of the earthing system will move towards
that of the most loaded line conductor. Such a rise in the potential of the neutral beyond the break is
known as a neutral inversion. Therefore, TN-C connections must not go across plug/socket connections
or flexible cables, where there is a higher probability of contact problems than with fixed wiring. There is
also a risk if a cable is damaged, which can be mitigated by the use of concentric cable construction and
multiple earth electrodes. Due to the (small) risks of the lost neutral raising 'earthed' metal work to a
dangerous potential, coupled with the increased shock risk from proximity to good contact with true earth,
the use of TN-C-S supplies is banned in the UK for caravan sites and shore supply to boats, and strongly
discouraged for use on farms and outdoor building sites, and in such cases it is recommended to make all
outdoor wiring TT with RCD and a separate earth electrode.
 In IT systems, a single insulation fault is unlikely to cause dangerous currents to flow through a human
body in contact with earth, because no low-impedance circuit exists for such a current to flow. However,
a first insulation fault can effectively turn an IT system into a TN system, and then a second insulation
fault can lead to dangerous body currents. Worse, in a multi-phase system, if one of the line conductors
made contact with earth, it would cause the other phase cores to rise to the phase-phase voltage relative to
earth rather than the phase-neutral voltage. IT systems also experience larger transient overvoltage than
other systems.
 In TN-C and TN-C-S systems, any connection between the combined neutral-and-earth core and the body
of the earth could end up carrying significant current under normal conditions, and could carry even more
under a broken neutral situation. Therefore, main equipotential bonding conductors must be sized with
this in mind; use of TN-C-S is inadvisable in situations such as petrol stations, where there is a
combination of lots of buried metalwork and explosive gases.

Electromagnetic compatibility

 In TN-S and TT systems, the consumer has a low-noise connection to earth, which does not suffer from
the voltage that appears on the N conductor as a result of the return currents and the impedance of that
 conductor. This is of particular importance with some types of telecommunication and measurement
equipment.
 In TT systems, each consumer has its own connection to earth, and will not notice any currents that may
be caused by other consumers on a shared PE line.

Regulations

 In the United States National Electrical Code and Canadian Electrical Code the feed from the distribution
transformer uses a combined neutral and grounding conductor, but within the structure separate neutral
and protective earth conductors are used (TN-C-S). The neutral must be connected to earth only on the
supply side of the customer's disconnecting switch.
 In Argentina, France (TT) and Australia (TN-C-S), the customers must provide their own ground
connections.
 Japan is governed by PSE law, and uses TT earthing in most installations.
 In Australia, the Multiple Earthed Neutral (MEN) earthing system is used and is described in Section 5 of
AS 3000. For an LV customer, it is a TN-C system from the transformer in the street to the premises, (the
neutral is earthed multiple times along this segment), and a TN-S system inside the installation, from the
Main Switchboard downwards. Looked at as a whole, it is a TN-C-S system.
 In Denmark the high voltage regulation and Malaysia the Electricity Ordinance 1994 states that all
consumers must use TT earthing, though in rare cases TN-C-S may be allowed (used in the same manner
as in the United States). Rules are different when it comes to larger companies.
 In India as per Central Electricity Authority Regulations, CEAR, 2010, rule 41, there is provision of
earthing, neutral wire of a 3-phase, 4-wire system and the additional third wire of a 2- phase, 3-wire
system. Earthing is to be done with two separate connections. Grounding system also to have minimum
two or more earth pits (electrode) such that proper grounding takes place. As per the rule 42, installation
with load above 5 kW exceeding 250 V shall have suitable Earth leakage protective device to isolate the
load in case of earth fault or leakage. Application examples

 In the areas of UK where underground power cabling is prevalent, the TN-S system is common.
 In India LT supply is generally through TN-S system. Neutral is double grounded at distribution
transformer. Neutral and earth run separately on distribution overhead line/cables. Separate conductor for
overhead lines and armoring of cables are used for earth connection. Additional earth electrodes/pits are
installed at user ends for strengthening earth.
 Most modern homes in Europe have a TN-C-S earthing system. The combined neutral and earth occurs
between the nearest transformer substation and the service cut out (the fuse before the meter). After this,
separate earth and neutral cores are used in all the internal wiring.
 Older urban and suburban homes in the UK tend to have TN-S supplies, with the earth connection
delivered through the lead sheath of the underground lead-and-paper cable.
  Older homes in Norway uses the IT system while newer homes use TN-C-S.
 Some older homes, especially those built before the invention of residual-current circuit breakers and
wired home area networks, use an in-house TN-C arrangement. This is no longer recommended practice.
 Laboratory rooms, medical facilities, construction sites, repair workshops, mobile electrical installations,
and other environments that are supplied via engine-generators where there is an increased risk of
insulation faults, often use an IT earthing arrangement supplied from isolation transformers. To mitigate
the two-fault issues with IT systems, the isolation transformers should supply only a small number of
loads each and should be protected with an insulation monitoring device (generally used only by medical,
railway or military IT systems, because of cost).
 In remote areas, where the cost of an additional PE conductor outweighs the cost of a local earth
connection, TT networks are commonly used in some countries, especially in older properties or in rural
areas, where safety might otherwise be threatened by the fracture of an overhead PE conductor by, say, a
fallen tree branch. TT supplies to individual properties are also seen in mostly TN-C-S systems where an
individual property is considered unsuitable for TN-C-S supply.
 In Australia, New Zealand and Israel the TN-C-S system is in use; however, the wiring rules state that, in
addition, each customer must provide a separate connection to earth, via a dedicated Earth electrode. (Any
metallic water pipes entering the consumer's premises must also be "bonded" to the Earthing point at the
distribution panel.) In Australia and New Zealand this is called the Multiple Earthed Neutral Link or
MEN Link. This MEN Link is removable for installation testing purposes, but is connected during use by
either a locking system (locknuts for instance) or two or more screws. In the MEN system, the integrity of
the Neutral is paramount. In Australia, new installations must also bond the foundation concrete re-
enforcing under wet areas to the earth conductor (AS3000), typically increasing the size of the earthing,
and provides an equipotential plane in areas such as bathrooms. In older installations, it is not uncommon
to find only the water pipe bond, and it is allowed to remain as such, but the additional earth electrode
must be installed if any upgrade work is done. The protective earth and neutral conductors are combined
until the consumer's neutral link (located on the customer's side of the electricity meter's neutral
connection) – beyond this point, the protective earth and neutral conductors are separate.

High-voltage systems

In high-voltage networks (above 1 kV), which are far less accessible to the general public, the focus of
earthing system design is less on safety and more on reliability of supply, reliability of protection, and
impact on the equipment in presence of a short circuit. Only the magnitude of phase-to-ground short
circuits, which are the most common, is significantly affected with the choice of earthing system, as the
current path is mostly closed through the earth.
Three-phase HV/MV power transformers, located in distribution substations, are the most common
source of supply for distribution networks, and type of grounding of their neutral determines the earthing
system. There are five types of neutral earthing:

 Solid-earthed neutral
 Unearthed neutral
 Resistance-earthed neutral
o Low-resistance earthing
o High-resistance earthing
 Reactance-earthed neutral
 Using earthing transformers (such as the Zigzag transformer)

Solid-earthed neutral

In solid or directly earthed neutral, transformer's star point is directly connected to the ground. In this
solution, a low-impedance path is provided for the ground fault current to close and, as result, their
magnitudes are comparable with three-phase fault currents. Since the neutral remains at the potential
close to the ground, voltages in unaffected phases remain at levels similar to the pre-fault ones; for that
reason, this system is regularly used in high-voltage transmission networks, where insulation costs are
high.

Resistance-earthed neutral

To limit short circuit earth fault an additional neutral earthing resistor (NER) is added between the
neutral of transformer's star point and earth.

Low-resistance earthing

With low resistance fault current limit is relatively high. In India it is restricted for 50 A for open cast
mines as per Central Electricity Authority Regulations, CEAR, 2010, rule 100.

High-resistance earthing

High resistance grounding system grounds the neutral through a resistance which limits the ground fault
current to a value equal to or slightly greater than the capacitive charging current of that system
Unearthed neutral

In unearthed, isolated or floating neutral system, as in the IT system, there is no direct connection of the
star point (or any other point in the network) and the ground. As a result, ground fault currents have no
path to be closed and thus have negligible magnitudes. However, in practice, the fault current will not be
equal to zero: conductors in the circuit — particularly underground cables — have an inherent
capacitance towards the earth, which provides a path of relatively high impedance.

Systems with isolated neutral may continue operation and provide uninterrupted supply even in presence
of a ground fault. However, while the fault is present, the potential of other two phases relative to the
ground reaches of the normal operating voltage, creating additional stress for the insulation; insulation
failures may inflict additional ground faults in the system, now with much higher currents.

Presence of uninterrupted ground fault may pose a significant safety risk: if the current exceeds 4 A –
5 A an electric arc develops, which may be sustained even after the fault is cleared. For that reason, they
are chiefly limited to underground and submarine networks, and industrial applications, where the
reliability need is high and probability of human contact relatively low. In urban distribution networks
with multiple underground feeders, the capacitive current may reach several tens of amperes, posing
significant risk for the equipment.

The benefit of low fault current and continued system operation thereafter is offset by inherent drawback
that the fault location is hard to detect.
Earthing and Electrical Grounding Installation

What is Grounding or Earthing?

To connect the metallic (conductive) Parts of an Electric appliance or installations to the earth (ground) is called
Earthing or Grounding.

In other words, to connect the metallic parts of electric machinery and devices to the earth plate or earth electrode
(which is buried in the moisture earth) through a thick conductor wire (which has very low resistance) for safety
purpose is known as Earthing or grounding.

To earth or earthing rather, means to connect the part of electrical apparatus such as metallic covering of metals,
earth terminal of socket cables, stay wires that do not carry current to the earth. Earthing can be said as the
connection of the neutral point of a power supply system to the earth so as to avoid or minimize danger during
discharge of electrical energy.
Difference between Earthing, Grounding and Bonding.

Earthing and Grounding is the same terms used for earthing. Grounding is the commonly word used
for earthing in the North American standards like IEEE, NEC, ANSI and UL e.t.c while, Earthing is
used in European, Common wealth countries and Britain standards like IS and IEC etc.

The word Bonding used for jointing two wires (as well as conductors, pipes or appliances together.
Bonding is known as connecting the metallic parts of different machines which is not considered to be
carrying electric current during normal operation of the machines to bring them at the same level of electric
potential.

Why Earthing is Important?

The primary purpose of earthing is to avoid or minimize the danger of electrocution, fire due to earth
leakage of current through undesired path and to ensure that the potential of a current carrying conductor
does not rise with respect to the earth than its designed insulation.

When the metallic part of electrical appliances (parts that can conduct or allow passage of electric current)
comes in contact with a live wire, maybe due to failure of installations or failure in cable insulation, the
metal become charged and static charge accumulates on it. If a person touches such a charged metal,
the result is a severe shock.

To avoid such instances, the power supply systems and parts of appliances have to be earthed so as to
transfer the charge directly to the earth.

Below are the basic needs of Earthing.

 To protect human lives as well as provide safety to electrical devices and appliances from leakage
current.
 To keep voltage as constant in the healthy phase (If fault occurs on any one phase).
 To Protect Electric system and buildings form lighting.
 To serve as a return conductor in electric traction system and communication.
 To avoid the risk of fire in electrical installation systems.
Different Terms used in Electrical Earthing

 Earth: The proper connection between electrical installation systems via conductor to the buried
plate in the earth is known as Earth.
 Earthed: When an electrical device, appliance or wiring system connected to the earth through
earth electrode, it is known as earthed device or simple “Earthed”.
 Solidly Earthed: When an electric device, appliance or electrical installation is connected to the
earth electrode without a fuse, circuit breaker or resistance/Impedance, It is called “solidly
earthed”.
 Earth Electrode: When a conductor (or conductive plate) buried in the earth for electrical earthing
system. It is known to be Earth Electrode. Earth electrodes are in different shapes like, conductive
plate, conductive rod, metal water pipe or any other conductor with low resistance.
 Earthing Lead: The conductor wire or conductive strip connected between Earth electrode and
Electrical installation system and devices in called Earthing lead.
 Earth Continuity Conductor: The conductor wire, which is connected among different electrical
devices and appliances like, distribution board, different plugs and appliances etc. in other words,
the wire between earthing lead and electrical device or appliance is called earth continuity
conductor. It may be in the shape of metal pipe (fully or partial), or cable metallic sheath or flexible
wire.
 Sub Main Earthing Conductor: A wire connected between switch board and distribution board
i.e. that conductor is related to sub main circuits.
 Earth Resistance: This is the total resistance between earth electrode and earth in Ω (Ohms).
Earth resistance is the algebraic sum of the resistances of earth continuity conductor, earthing lead,
earth electrode and earth.

Points to Be Earthed

Earthing is not done anyhow. According to IE rules and IEE (Institute of Electrical Engineers) regulations,

 Earth pin of 3-pin lighting plug sockets and 4-pin power plug should be efficiently and
permanently earthed.
 All metal casing or metallic coverings containing or protecting any electric supply line or apparatus
such as GI pipes and conduits enclosing VIR or PVC cables, iron clad switches, iron clad
distribution fuse boards e.t.c should be earthed (connected to earth).
  The frame of every generator, stationary motors and metallic parts of all transformers used for
controlling energy should be earthed by two separate and yet distinct connections with the earth.
 In a dc 3-wire system, the middle conductors should be earthed at the generating station.
 Stay wires that are for overhead lines should be connected to earth by connecting at least one strand
to the earth wires.

Components of Earthing System

A complete electrical earthing system consists on the following basic components.

 Earth Continuity Conductor

 Earthing Lead
 Earth Electrode
Earth Continuity Conductor or Earth Wire

That part of the earthing system which interconnects the overall metallic parts of electrical installation e.g.
conduit, ducts, boxes, metallic shells of the switches, distribution boards, Switches, fuses, Regulating and
controlling devices, metallic parts of electrical machines such as, motors, generators, transformers and the
metallic framework where electrical devices and components are installed is known as earth wire or earth
continuity conductor as shown in the above figure.

The resistance of the earth continuity conductor is very low. According to IEEE rules, resistance between
consumer earth terminal and earth Continuity conductor (at the end) should not be increased than 1Ω. In
simple words, resistance of earth wire should be less than 1Ω.

Size of the Earth Continuity Conductor or Earth Wire depends on the cable size used in the wiring circuit.

Size of Earth Continuity Conductor

The cross sectional area of the Earth Continuity Conductor should not be less than the half of the cross
sectional area of the thickest wire used in the electrical wiring installation.

Generally, the size of the bare copper wire used as earth continuity conductor is 3SWG. But keep in mind
that, don’t use less than 14SWG as earth wire. Copper strip is also can be used as earth continuity
conductor instead of bare copper wire but don’t go for it until manufacture recommend it.

Earthing Lead or Earthing Joint

The conductor wire connected between earth continuity conductor and earth electrode or earth plate is
called earthing joint or “Earthing lead”. The point where earth continuity conductor and earth electrode
meet is known as “connecting point” as shown in the above figure.

Earthing lead is the final part of the earthing system which is connected to the earth electrode (which is
underground) through earth connecting point. There should be minimum joints in earthing lead as well as
lower in size and straight in the direction.

Generally, copper wire can be used as earthing lead but, copper strip is also used for high installation and
it can handle the high fault current because of wider area than the copper wire.
A hard drawn bare copper wire is also used as an earthing lead. In this method, all earth conductors
connected to a common (one or more) connecting points and then, earthing lead is used to connect earth
electrode (earth plat) to the connecting point.

To increase the safety factor of installation, two copper wires are used as earthing lead to connect the
device metallic body to the earth electrode or earth plate. I.e. if we use two earth electrodes or earth plats,
there would be four earthing leads. It should not be considered that the two earth leads are used as parallel
paths to flow the fault currents but both paths should work properly to carry the fault current because it is
important for better safety.

Size of the Earthing Lead

The size or area of earthing lead should not be less than the half of the thickest wire used in the installation.

The largest size for earthing lead is 3SWG and the minimum size should not be less than 8SWG. If 37/.083
wire is used or the load current is 200A from the supply voltage, then it is recommended to use copper
strip instead of double earthing lead. The earth lead connection method is as shown in the above figure.
Earthing Electrode or Earth Plate

A metallic electrode or plate which is buried in the earth (underground) and it is the last part of the
electrical earthing system. In simple words, the final underground metallic (plate) part of the earthing
system which is connected with earthing lead is called earth plate or earth electrode.

A metallic plate, pipe or rode can be used as an earth electrode which has very low resistance and carry
the fault current safely towards ground (earth).

Size of Earthing Electrode

Both copper and iron can be used as earthing electrode. The size of earth electrode (In case of copper)

2×2 (two-foot-wide as well as in length) and 1/8-inch thickness. I.e. 2’ x 2’ x 1/8”. (600x600x300 mm)

In case of Iron

2’ x2’ x ¼” = 600x600x6 mm

It is recommended to bury the earth electrode in the moisture earth. If it is not possible, then put water in
the GI (Galvanized Iron) pipe to make possible the moisture condition.

In the earthing system, put the earth electrode in vertical position (underground) as shown in the above
fig. Also, put a 1 foot (about 30cm) layer of powdered charcoal and lime mixture around the earth plate
(don’t confuse with earth electrode and earth plate as both are the same thing).
This action makes the possible increase in the size of the earth electrode which leads a better continuity
in the earth (earthing system) and also helps to maintain the moisture condition around earth plate.

Good to know:

Don’t use coke (after burning coal in the furnace to emit all the gases and other components, the remaining
88% carbon is called coke) or stone coal instead of charcoal (wood coal) because it causes to corrosion in
the earth plate.

Since, the water level is different in the different areas; therefore, the depth for earth electrode installation
is also different in various areas. But, the depth for earth electrode installation should not be less than 10ft
(3 meter) and should below 1 foot (304.8mm) from the constant water level.

Motors, Generator, Transformers e.t.c should be connected from to earth electrode two different places.

Earth Plate or Earth Electrode Size for Small installation

In small installation, use metallic rod (diameter = 25mm (1inch) and length = 2m (6ft) instead of earth
plate for earthing system. The metallic pipe should be 2 meter below from the surface of ground. To
maintain the moister condition, put 25mm (1inch) coal and lime mixture around the earth plate.

For effectiveness and convenience, you may use the copper rods 12.5mm (0.5 inch) to 25mm (1 inch)
diameter and 4m (12ft) length. We will discuss the installation method of rod earthing latter.

Methods of Earthing | Types of Earthing

Earthing can be done in many ways. The various methods employed in earthing (in house wiring or factory
and other connected electrical equipment and machines) are discussed as follows:

1). Plate Earthing:

In plate earthing system, a plate made up of either copper with dimensions 60cm x 60cm x 3.18mm (i.e.
2ft x 2ft x 1/8 in) or galvanized iron (GI) of dimensions 60cm x 60cm x 6.35 mm (2ft x 2ft x ¼ in) is
buried vertical in the earth (earth pit) which should not be less than 3m (10ft) from the ground level.

For proper earthing system, follow the above mentioned steps in the (Earth Plate introduction) to maintain
the moisture condition around the earth electrode or earth plate.
2). Pipe Earthing:

A galvanized steel and a perforated pipe of approved length and diameter is placed vertically in
a wet soil in this kind of system of earthing. It is the most common system of earthing.

The size of pipe to use depends on the magnitude of current and the type of soil. The dimension
of the pipe is usually 40mm (1.5in) in diameter and 2.75m (9ft) in length for ordinary soil or
greater for dry and rocky soil. The moisture of the soil will determine the length of the pipe to be
buried but usually it should be 4.75m (15.5ft).
3). Rod Earthing

It is the same method as pipe earthing. A copper rod of 12.5mm (1/2 inch) diameter or 16mm
(0.6in) diameter of galvanized steel or hollow section 25mm (1inch) of GI pipe of length above
2.5m (8.2 ft) are buried upright in the earth manually or with the help of a pneumatic hammer.
The length of embedded electrodes in the soil reduces earth resistance to a desired value.
4). Earthing through the Waterman

In this method of earthing, the waterman (Galvanized GI) pipes are used for earthing purpose.
Make sure to check the resistance of GI pipes and use earthing clamps to minimize the
resistance for proper earthing connection.

If stranded conductor is used as earth wire, then clean the end of the strands of the wire and
make sure it is in the straight and parallel position which is possible then to connect tightly to the
waterman pipe.

5). Strip or Wire Earthing:

In this method of earthing, strip electrodes of cross-section not less than 25mm x 1.6mm (1in x
0.06in) is buried in a horizontal trenches of a minimum depth of 0.5m. If copper with a cross-
section of 25mm x 4mm (1in x 0.15in) is used and a dimension of 3.0mm 2 if it’s a galvanized iron
or steel.
If at all round conductors are used, their cross-section area should not be too small, say less
than 6.0mm2 if it’s a galvanized iron or steel. The length of the conductor buried in the ground
would give a sufficient earth resistance and this length should not be less than 15m.

General method of Earthing / Proper Grounding Installation (Step by Step)

The usual method of earthing of electric equipments, devices and appliances are as follow:

1. First of all, dig a 5x5ft (1.5×1.5m) pit about 20-30ft (6-9 meters) in the ground. (Note that, depth
and width depends on the nature and structure of the ground)
2. Bury an appropriate (usually 2’ x 2’ x 1/8” (600x600x300 mm) copper plate in that pit in vertical
position.
3. Tight earth lead through nut bolts from two different places on earth plate.
4. Use two earth leads with each earth plate (in case of two earth plates) and tight them.
5. To protect the joints from corrosion, put grease around it.
6. Collect all the wires in a metallic pipe from the earth electrode(s). Make sure the pipe is 1ft (30cm)
above the surface of the ground.
7. To maintain the moisture condition around the earth plate, put a 1ft (30cm) layer of powdered
charcoal (powdered wood coal) and lime mixture around the earth plate of around the earth plate.
8. Use thimble and nut bolts to connect tightly wires to the bed plates of machines. Each machine
should be earthed from two different places. The minimum distance between two earth electrodes
should be 10 ft. (3m).
9. Earth continuity conductor which is connected to the body and metallic parts of all installation
should be tightly connected to earth lead.
10. At last (but not least), test the overall earthing system through earth tester. If everything is going
about the planning, then fill the pit with soil. The maximum allowable resistance for earthing is 1Ω.
If it is more than 1 ohm, then increase the size (not length) of earth lead and earth continuity
conductors. Keep the external ends of the pipes open and put the water time to time to maintain
the moisture condition around the earth electrode which is important for the better earthing
system.
SI specification for Earthing

Various specifications in respect to earthing as recommended by Indian Standards are given

below. Here are few;

 An earthing electrode should not be situated (installed) close to the building whose installation
system is being earthed at least more than 1.5m away.
 The earth resistance should be low enough to cause the flow of current sufficient to operate the
protective relays or blow fuses. Its value is not constant as it varies with weather because it
depends on moisture (but should not be less than 1 Ohm).
 The earth wire and earth electrode will be the same material.
 The earthing electrode should always be placed in a vertical position inside the earth or pit so that
it may be in contact with all the different earth layers.

Dangers of Not Earthing a Supply System

As emphasized on earlier, earthing is provided in order

 To avoid electric shock

 To avoid risk of fire as a result of earth leakage current through unwanted path and
 To ensure that no current carrying conductor rises to a potential with respect to general mass of
earth than its designed insulation.

However, if excessive current is not earthed, appliances will be damaged without the help of
fuse in place. You should note that excessive current is earthed at their generating stations which
is why earth wires carries very little or no current at all. It therefore implies that it is not necessary
to earth any of the wires (live, earth and neutral wires) contained in a PVC. Earthing the live wire
is catastrophic.

I have seen a person killed simply because a live wire got cut from overhead pole and fell to the
ground while the ground was wet. Excessive current is earthed at generating stations and if at
all the earthing is not efficient due to fault, earth fault interrupters will be there to help. Fuse help
only when the power transmitted is above the rating of our appliances, it blocks the current from
reaching our appliances by blowing off and protecting our appliances in the process.

In our electrical appliances, if excessive currents are not earthed, we would experience severe
shock. Earthing takes place in electrical appliances only when there is a problem and it is to
save us from danger.
If in an electronic installation, a metallic part of an electrical appliance comes in direct contact
with a live wire that results from maybe failure of installation or otherwise, the metal will be
charged and static charge will accumulate on it.

If you happen to touch the metallic part at that moment you will be zapped. But if the metallic
part of the appliance is earthed, the charge will be transferred to earth instead of accumulating
on the metallic part of the appliance. Current don’t flow through earth wires in electrical
appliances, it does so only when there is problem and only to direct the unwanted current to
earth in order to protect us from severe shock.

In addition, if a live wire touches accidentally (in a faulty system) to the metallic part of a machine.
Now, if a man touches that metallic part of the machine, then the current will flow through their
body to the ground, hence, he will get shocked (electrocuted) which may lead to serious injuries
even to death. That’s why earthing is so important?