Earthing a circuit

[Arkandea]

What exactly is the effect of earthing a circuit, and why would someone want to do so?

Thanks in advance

[superflya]

https://student.ee.uwa.edu.au/practical-resources/earthprotdev

[simonhu81292]

SuperF ...
the site doesn't work ...

[superflya]

hmm works for me :/ ill paste the stuff

There are four basic reasons for earthing an electrical system:


1. REDUCTION OF SHOCK HAZARD

A person might receive an electric shock if an active conductor was to make contact with the exposed metalwork of an appliance. To help reduce this risk, all exposed metal parts of any appliance the user may come into contact with, must provide a low impedance path to ground for any active voltage that appears on the case or metalwork, which will help ensure that any circuit protective devices, such as fuses or circuit breakers are activated, which will remove the supply, making the faulty device safe. This earth is called a Protective Earth.


2. SAFE DISCONNECTION OF SUPPLY
If the exposed metalwork of an appliance were connected by a fault condition to an active conductor, the active current path needs to be able to flow to ground via a low impedance path so an excessive current will flow that will cause a protective device such as a fuse or circuit breaker to open the circuit, thus preventing an electric shock situation.
Circuit protection devices are also required to protect building wiring from overload currents, while allowing the maximum demand of the protected circuit.

Fuses
These can be fast blow, slow blow and semiconductor. An excess current causes the fuse to rupture or burn out, creating an open circuit. They have to be replaced every time they operate, but are low cost for most applications.

Circuit Breakers
These can magnetic which are current sensitive or thermal which rely on a heating effect to activate a mechanical switch. Circuit breakers can have different trip characteristics to suit apllications such as motor start, where an initial high inrush current can be withstood, but a high fault current will cause the circuit breaker to trip, thus disconnecting the overload.

RCD's or Residual Current Devices
An RCD monitors the current flowing into a circuit through the active conductor and out of a circuit through the neutral conductor, so that if an imbalance occurs, it will disconnect the supply as a fault condition has occurred and some current if flowing through to earth.. The sensitivity or trip current of the rcd varies depending on where it is used, for general applications it is set for 30 mA.It is important to remember that it does not provide protection for when a person makes contact between active and neutral as no imbalance will occur. It is primarily designed for an active to earth fault detection. It will NOT protect you from Active to Neutral or Active to Active polyphase contact.

3. MINIMISE THE DANGER OF FIRE HAZARD
 Should the equipment become faulty by the active wire touching the case, then current will rush to earth, smoke will rise from the equipment, and if the current is very high the fuse in the active line will blow, disconnecting mains power from the faulty appliance. Standards limiting current in any circuit are vital to prevent excessive heating of the power supply wires leading to fires.


4. VOLTAGE STABILITY
Neutral earthing : Star point of Wye connected transformers and alternator windings are earthed primarily to provide voltage stability to system on account of imbalance in loading resulting in neutral current flow. Neutral point allows vector sum of three phase currents displaced at 120 degrees nullifying it to zero. Secondary purpose served is detection of earth faults or earth leakages and allow the protective gear to operate in desired time.

In the view of high harmonic contents found in modern facilities, the zero sequence or triplen harmonic currents overload the neutrals if not adequately sized. This is because these are in phase and hence do not cancel out at neutral point. So neutrals are required to be sized equal to or sometimes double the size of line conductors to carry "algebraic sum" of triplen components in the lines.

Neutral earthing for applicable to low voltage distribution systems upto 1000 V ac comprise of solid earthing with no intentional resistance connected in the path.

try this http://www.rfi-ind.com.au/download/earthing%20rev2%200700.pdf

[physics]

hmm works for me :/ ill paste the stuff

There are four basic reasons for earthing an electrical system:


1. REDUCTION OF SHOCK HAZARD

A person might receive an electric shock if an active conductor was to make contact with the exposed metalwork of an appliance. To help reduce this risk, all exposed metal parts of any appliance the user may come into contact with, must provide a low impedance path to ground for any active voltage that appears on the case or metalwork, which will help ensure that any circuit protective devices, such as fuses or circuit breakers are activated, which will remove the supply, making the faulty device safe. This earth is called a Protective Earth.


2. SAFE DISCONNECTION OF SUPPLY
If the exposed metalwork of an appliance were connected by a fault condition to an active conductor, the active current path needs to be able to flow to ground via a low impedance path so an excessive current will flow that will cause a protective device such as a fuse or circuit breaker to open the circuit, thus preventing an electric shock situation.
Circuit protection devices are also required to protect building wiring from overload currents, while allowing the maximum demand of the protected circuit.

Fuses
These can be fast blow, slow blow and semiconductor. An excess current causes the fuse to rupture or burn out, creating an open circuit. They have to be replaced every time they operate, but are low cost for most applications.

Circuit Breakers
These can magnetic which are current sensitive or thermal which rely on a heating effect to activate a mechanical switch. Circuit breakers can have different trip characteristics to suit apllications such as motor start, where an initial high inrush current can be withstood, but a high fault current will cause the circuit breaker to trip, thus disconnecting the overload.

RCD's or Residual Current Devices
An RCD monitors the current flowing into a circuit through the active conductor and out of a circuit through the neutral conductor, so that if an imbalance occurs, it will disconnect the supply as a fault condition has occurred and some current if flowing through to earth.. The sensitivity or trip current of the rcd varies depending on where it is used, for general applications it is set for 30 mA.It is important to remember that it does not provide protection for when a person makes contact between active and neutral as no imbalance will occur. It is primarily designed for an active to earth fault detection. It will NOT protect you from Active to Neutral or Active to Active polyphase contact.

3. MINIMISE THE DANGER OF FIRE HAZARD
 Should the equipment become faulty by the active wire touching the case, then current will rush to earth, smoke will rise from the equipment, and if the current is very high the fuse in the active line will blow, disconnecting mains power from the faulty appliance. Standards limiting current in any circuit are vital to prevent excessive heating of the power supply wires leading to fires.


4. VOLTAGE STABILITY
Neutral earthing : Star point of Wye connected transformers and alternator windings are earthed primarily to provide voltage stability to system on account of imbalance in loading resulting in neutral current flow. Neutral point allows vector sum of three phase currents displaced at 120 degrees nullifying it to zero. Secondary purpose served is detection of earth faults or earth leakages and allow the protective gear to operate in desired time.

In the view of high harmonic contents found in modern facilities, the zero sequence or triplen harmonic currents overload the neutrals if not adequately sized. This is because these are in phase and hence do not cancel out at neutral point. So neutrals are required to be sized equal to or sometimes double the size of line conductors to carry "algebraic sum" of triplen components in the lines.

Neutral earthing for applicable to low voltage distribution systems upto 1000 V ac comprise of solid earthing with no intentional resistance connected in the path.

try this http://www.rfi-ind.com.au/download/earthing%20rev2%200700.pdf

THATS like in our physics textbook..like 2 pages dedicated to it D: aksfjlkdsjfdsfjbadstufffflgjdlkgjlksg