Bonding,
Grounding and Earthing
In Fire detection system or CCTV / Access
Control System this 3 terms are very important during doing the errection,
testing & commissioning activity.
- Bonding is more clear word compare to Grounding and Earthing but there is a micro difference between Grounding and Earhing.
- Earthing and Grounding are actually different terms for expressing the same concept. Ground or earth in a mains electrical wiring system is a conductor that provides a low impedance path to the earth to prevent hazardous voltages from appearing on equipment. Earthing is more commonly used in Britain, European and most of the commonwealth countries standards (IEC, IS), while Grounding is the word used in North American standards (NEC, IEEE, ANSI, UL).
- We understand that Earthing and Grounding are necessary. We need to understand that there are really two separate things we are doing for same purpose that we call Grounding or Earthing.
- The Earthing is to reference our electrical source to earth (usually via connection to some kind of rod driven into the earth or some other metal that has direct contact with the earth).
- The grounded circuits of machines need to have an effective return path from the machines to the power source in order to function properly (Here by Neutral Circuit).
- In addition, non-current-carrying metallic components in a System, such as equipment cabinets, enclosures, and structural steel, need to be electrically interconnected and earthed properly so voltage potential cannot exist between them. However, troubles can arise when terms like “bonding,” “grounding,” and “earthing” are interchanged or confused in certain situations.
- In TN Type Power Distribution System, in US NEC (and possibly other) usage: Equipment is earthed to pass fault Current and to trip the protective device without electrifying the device enclosure. Neutral is the current return path for phase. These Earthing conductor and Neutral conductor are connected together and earthed at the distribution panel and also at the street, but the intent is that no current flow on earthed ground, except during momentary fault conditions. Here we may say that Earthing and grounding are nearly same by practice.
- But In the TT Type Power Distribution System (In India) Neutral is only earthed (here it is actually called Grounding) at distribution source (at distribution transformer) and Four wires (Neutral and Three Phase) are distributed to consumer. While at consumer side all electrical equipments body are connected and earthed at consumer premises (here it is called Earthing). Consumer has no any permission to mix Neutral with earth at his premises here Earthing and grounding is the different by practice.
But in both above case Earthing and Grounding
are used for the same Purpose. Let’s try to understand this terminology one by
one.
Bonding:
§ Bonding is simply the act of joining two
electrical conductors together. These may be two wires, a wire and a pipe, or
these may be two Equipment’s.
§ Bonding has to be done by connecting of
all the metal parts that are not supposed to be carrying current during normal
operations to bringing them to the same electrical potential.
§ Bonding ensures that these two things which are
bonded will be at the same electrical potential. That means we would not get
electricity building up in one equipment or between two different equipment. No
current flow can take place between two bonded bodies because they have the
same potential.
§ Bonding, itself, does not protect
anything. However, if one of those boxes is earthed there can be no
electrical energy build-up. If the grounded box is bonded to the other box, the
other box is also at zero electrical potential.
§ It protects equipment & Person by reducing
current flow between pieces of equipment at different potentials.
§ The primary reason for bonding is personnel
safety, so someone touching two pieces of equipment at the same time does not
receive a shock by becoming the path of equalization if they happen to be at
different potentials.
§ The Second reason has to do with what happens if
Phase conductor may be touched an external metal part. The bonding helps to
create a low impedance path back to the source. This will force a large current
to flow, which in turn will cause the breaker to trip. In other words, bonding
is there to allow a breaker to trip and thereby to terminate a fault.
§ Bonding to electrical earth is
used extensively to ensure that all conductors (person, surface and
product) are at the same electrical potential. When all
conductors are at the same potential no discharge can occur.
Earthing:
§ Earthing means connecting the dead part (it
means the part which does not carries current under normal condition) to the
earth for example electrical equipment’s frames, enclosures, supports etc.
§ The purpose of earthing is to minimize risk of
receiving an electric shock if touching metal parts when a fault is present.
Generally green wire is used for this as a nomenclature.
§ Under fault conditions the non-current carrying
metal parts of an electrical installation such as frames, enclosures, supports,
fencing etc. may attain high potential with respect to ground so that any
person or stray animal touching these or approaching these will be subjected to
potential difference which may result in the flow of a current through the body
of the person or the animal of such a value as may prove fatal.
§ To avoid this non-current carrying metal parts
of the electrical system are connected to the general mass of earth by means of
an earthing system comprising of earth conductors to conduct the fault currents
safely to the ground.
§ Earthing has been accomplished through bonding
of a metallic system to earth. It is normally achieved by inserting ground rods
or other electrodes deep inside earth.
§ Earthing is to ensure safety or
Protection of electrical equipment and Human by discharging the
electrical energy to the earth.
Grounding:
§ Grounding means connecting the live part (it
means the part which carries current under normal condition) to the earth for
example neutral of power transformer.
§ Grounding is done for the protections of power
system equipment and to provide an effective return path from the machine to
the power source. For example grounding of neutral point of a star connected
transformer.
§ Grounding refers the current carrying part of
the system such as neutral (of the transformer or generator).
§ Because of lightening, line surges or
unintentional contact with other high voltage lines, dangerously high voltages
can develop in the electrical distribution system wires. Grounding provides a
safe, alternate path around the electrical system of your house thus minimizing
damage from such occurrences.
§ Generally Black wire is used for this as a
nomenclature.
§ All electrical/electronic circuits (AC & DC)
need a reference potential (zero volts) which is called ground in order to make
possible the current flow from generator to load. Ground is May or May not
be earthed. In Electrical Power distribution it is either earthed at
distribution Point or at Consumer end but it is not earthed in Automobile( for
instance all vehicles’ electrical circuits have ground connected to the chassis
and metallic body that are insulated from earth through tires). There may exist
a neutral to ground voltage due to voltage drop in the wiring,
thus neutral does not necessarily have to be at ground potential.
§ In a properly balanced system, the phase
currents balance each other, so that the total neutral current is also zero.
For individual systems, this is not completely possible, but we strive to come
close in aggregate. This balancing allows maximum efficiency of the distribution
transformer’s secondary winding
Difference between Earthing & Grounding:
There is no major difference between earthing
and Grounding, both means “Connecting an electrical circuit or device to
the Earth”. This serves various purposes like to drain away unwanted
currents, to provide a reference voltage for circuits needing one, to lead
lightning away from delicate equipment. Even though there is a micro difference
between grounding & earthing.
(1) Difference in
Terminology:
§ In USA term Grounding is used but in UK term
Earthing is used.
(2) Balancing the Load Vs
Safety:
§ Ground is a source for unwanted currents and
also as a return path for main current some times. While earthing is done not
for return path but only for protection of delicate equipment’s. It is an
alternate low resistance path for current.
§ When we take out the neutral for a three phase
unbalanced connection and send it to ground, it is called grounding. Grounding
is done to balance unbalanced load. While earthing is used between the equipment
and earth pit so as to avoid electrical shock and equipment damage.
(3) Equipment Protection
Vs Human Safety:
§ Earthing is to protect the circuit elements
whenever high voltage is passed by thunders or by any other sources while
Grounding is the common point in the circuit to maintain the voltage levels.
§ Earth is used for the safety of the human body
in fault conditions while Grounding (As neutral earth) is used for the
protection of equipment’s.
§ Earthing is a preventive measure while Grounding
is just a return path
§ The ground conductor provides a return path for
fault current when a phase conductor accidentally comes in contact with a
grounded object. This is a safety feature of the wiring system and we would
never expect to see grounding conductor current flow during normal operation.
§ Do not Ground the Neutral Second time When It is
grounded either at Distribution Transformer or at Main service Panel of
Consumer end.
§ Grounding act as neutral. But neutral cannot act
as ground.
(4) System Zero Potential
Vs Circuit Zero Potential:
§ Earthing and Grounding both is refer to zero
potential but the system connected to zero potential is differ than
Equipment connected to zero potential .If a neutral point of a generator or
transformer is connected to zero potential then it is known as grounding.
At the same time if the body of the transformer or generator is connected to
zero potential then it is known as earthing.
§ The term “Earthing means that the circuit is
physically connected to the ground and it is Zero Volt Potential to the Ground
(Earth) but in case of “Grounding” the circuit is not physically connected to
ground, but its potential is zero(where the currents are algebraically
zero) with respect to other point, which is also known as “Virtual Grounding.”
§ Earth having zero potential
whereas neutral may have some potential. That means neutral does not
always have zero potential with respect to ground. In earthing we have Zero
Volt potential references to the earth while in grounding we have local
Zero Volt potential reference to circuit. When we connect two different Power
circuits in power distribution system, we want to have the same Zero Volt
reference so we connect them and grounds together. This common reference might
be different from the earth potential.
Illegal Practice of interchange Purpose of Grounding & Earthing wire
§ Neutral wire in grid connections is mandatory
for safety. Imagine a person from 4th floor in a building uses Earth wire
(which is earthed in the basement at Basement) as neutral to power
his lights. Another Person from 2nd floor has a normal setup and uses neutral
for the same purpose. Neutral wire is also earthed at the ground level (as per
USA practice Neutral is Grounded (earthed) at Building and as per Indian
Practice it is Grounded (earthed) at Distribution Transformer).
However, ground wire (Neutral wire) has a much lower electrical
resistance than Earth Wire (Earthing) which results in a difference
of electrical potential (i.e. voltage) between them. This voltage is quite a
hazard for anyone touching a Earth wire (Metal Body of Equipment) as it may
have several tens of volts.
§ The second issue is legality. Using ground wire
instead of neutral makes you an energy thief as the meter uses only the Phase
and neutral for recording your energy consumption. Many Consumers make energy
theft by using Earthing wire as a Neutral wire in an Energy meter.
Conclusion:
Ground is a source for unwanted currents and
also as a return path for main current. While earthing is done not for return
path but only for protection of delicate equipment’s. It is an alternate low
resistance path for current. Earth is used for the safety of the human body in
fault conditions while Grounding (As neutral earth) is used for the protection
of equipment’s.
