basics of electrical grounding earthing and bonding

Electrical Grounding• Grounding: the intentional and

permanent connection between

neutral and ground

• Ground Fault: unintentional connection

between an energized conductor and

ground

• 90% electrical faults are ground faults

Purpose of Grounding , Earthling , Bonding

• Personal safety ( Fire, Injury)

• Ensure operation of protective devices

Types of Grounding

• Isolated ground (Ungrounded)

• Solid or effective ground

• Low impedance ground

• High impedance ground

Ungrounded power system

Advantages Low fault current for line-to-ground faults

(typically < 5A)

No Arc Flash Hazard for ground faults

Continue operation during FIRST ground fault

Ungrounded power systemDisadvantages

Difficult to locate ground faults

Severe transient over-voltages possible during ground faults

Higher costs due to labor and downtime

locating ground faults

Second ground fault on another phase will

result in phase-phase fault

Ungrounded power system

Ungrounded power system

Solidly Grounded System

Very high ground fault currents• Fault must be cleared, shutting down

equipment.• Generators may not be rated for ground fault

Tremendous amount of arc flash / blast energy

• Equipment and people are not rated for energy

ARC FLASH

ARC FLASH• Dangerous condition associated with

release of energy caused by an electrical arc

• Burns resulting from arc flash and ignition of flammable cloths

• Arc temperature can reach 35000 F

• Fatal burn can occur at distance over 10 ft.

Before and After Arc Flash

Grounded power system

Grounded power system

Grounding through zigzag transformer

Electrical Bonding

• Bonding: connection of all non-current

carrying conductive parts of a distribution

system together to form a bonding system

• Bonding System is connected to the

Grounding Electrode by a Grounding

Conductor

• Bonding is not affected by the choice of

power system grounding

Without Bonding

Bonding

Live, Neutral, Earth & Fuses

L

N

E

Electrocution

Ground Fault

Electric shock ( when Grounding is not proper )

Fault sense by ELCB

Protective Earth Connection(Earthing)

• A protective earth (PE) connection ensures that all exposed conductive surfaces are at the same electrical potential as the surface of the Earth, to avoid the risk of electrical shock if a person touches a device in which an insulation fault has occurred. It ensures that in the case of an insulation fault (a "short circuit"), a very high current flows, which will trigger an overcurrent protection device (fuse, circuit breaker) that disconnects the power supply.

Functional Earth Connection• A functional earth connection serves a

purpose other than providing protection against electrical shock. In contrast to a protective earth connection, a functional earth connection may carry a current during the normal operation of a device. Functional earth connections may be required by devices such as surge suppression and electromagnetic-compatibility filters, some types of antennas and various measurement instruments. Generally the protective earth is also used as a functional earth, though this requires care in some situations

IT Network

TT Network

TN-S earthing system

TN-C earthing system

TN-C-S earthing system

• 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 In a

• TT earthing system, the protective earth connection of the consumer is provided by a local connection to earth, independent of any earth connection at the generator

• 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 RCD protection, and often an expensive time-delay type is needed to provide discrimination with an RCD downstream.

• In TN, an insulation fault is very likely to lead to a high short-circuit current that will trigger an overcurrent circuit-breaker or fuse and disconnect the L conductors.

• In the majority of TT systems, the earth fault loop impedance will be too high to do this, and so an RCD must be employed

• In TN-S and TT systems (and in TN-C-S beyond the point of the split), a residual-current device can be used as an 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 10-500 mA).

• 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, and it is dangerous to do this in a TN-C system