Earthing

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And very good answer I wish I could without hurting our new member

Hello Sri - please google as advise, you will be surprised the amount of information.

If still some doubt, come to us for clarifications

Let me try a succinct response: Earthing/grounding is used for safety and signal control. Suppose the circuits generating electrical voltages are in some way connect to conducting material which is large enough that the impedance between any two parts of it is small. If some of that voltage appears in another part of the circuit but is not wanted then it can often be removed by arranging for the unwanted voltage to return to its source via the low impedance large conducting material.

A couple of points worth mentioning. In UK usage "Earthing" usually refers to mains electrical connections that quite often literally go to a metal stake hammered into the soil outside the building (The world being a large body made of substatially conducting material). In UK usage "ground" usually refers to a "circuit ground" which may be the metal case the equipment is housed in or a printed circuit board area which is a large area of copper connected to that part of the circuit which is most conventiently considered as "zero volt". You will find that most voltage measurements in the circuit are made with the other terminal of the voltmeter connected here. I believe that North American terminology is the reverse of this ("ground" for ac mains; "earth" for signal reference planes).

It is often possible to design systems that operate without "grounds" or "earths". For instance ac mains safety can be achieved (possibly better) by "double insulation" and stopping signals getting to where they are not wanted can be achieved (possibly better) by careful design often involving balanced circuits (forcing currents to flow back to their source along a route that is closely as possible to the way they came) and careful filtering (a good example of this is ethernet LANs running over Cat5 or Cat 6 cable).

Earthing is a term that causes confusion to me. Do you mean connection to mother earth or do you mean bonding the equipment so that there is no difference in voltage potential?

i mean to connection to mother earth..

Are you asking about making a connection to mother earth or are you bonding or grounding ellectrical equipment?

Are your referring to making a connection to mother earth or bonding all of the metal parts of the electrical system together?

i am referring to making a connection to mother earth

Hi all,

Earthing is needed to close the circuit. For any source even if it a fault at far end of the transmission line, the fault current flows through the earth and return back to its source (may be a power transformer which is feeding the line). Without that the circuit will not be completed.

So if you dont earth your equipment, for example transformer, your winding gets all the fault current and will be subjected high mechanical forces which is not good for the windings. So we need a safer path for the fault current to flow which is nothing but earthing

I'm not quite sure what the last contribution (from "Guest") was trying to say.

As I understand it if you don't earth/ground the case work of your equipment the safety hazard is that a fault condition which allows a live conductor to come into contact with the case will make the case live and could give a shock to anyone touching it. If the case is earthed and a live conductor touched the case then current will flow back to the source (assuming that the source has one side connected to earth/ground). The assumption is that sufficient current will flow to cause protection devices in the supply to trigger and switch off the current. If the impedance of the return path is too high this might not be the case and current would continue to flow. This is why earthing/grounding systems usually have to have their resistance assessed to make sure that are low.

An additional reason for earthing/grounding equipment is for limiting the extent to which the equipment will produce radio interference. This particularly applies to computer type equipment. Should you ever encounter a desktop computer with a metal case where the earth/ground connection is missing you will probably find that the case has actually assumed a voltage at half of the ac line voltage (albeit via a high impedance so it should not be hazardous). This is because there are components (usually capacitors in the 100s nF region) connecting both the phase and neutral ac mains lines to the earth/ground within the computer power supply.

Earthing , per the original poster, means a connection to mother earth(dirt). Earthing a piece of equipment will not provide safety in the event of a fault. The resistance of the earth is too high to allow enough current flow to trip a breaker. Bonding or grounding the equipment is the method used in the US to cause the breaker to trip. An Equipment Grounding Conductor EGC is installed with the power conductor and connected to the equipment. The EGC is bonded to the metal frame at one end and to the Main Switch and grounding electrode at the other end. This provides a path for the fault current to flow.

Please see following links to understand What is earthing in electrical system

http://picearthingtech.com/

Regards

Raju

Electrical Earthing and Circuit Protective Devices

Electrical Earthing and Circuit Protective Devices Reasons For Earthing

There are four basic reasons for Earthing an electrical system:

REDUCTION OF SHOCK HAZARD

An earthed chassis will provide a low impedance path to ground for any active voltage that appears on the case or metalwork.

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 circuit, thus prenting an electric shock situation.

MINIMISE THE DANGER OF FIRE HAZARD

The earth wire should always be in good contact with all metal parts of any appliance the user may touch. 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. Without the earth wire, this fault would go undetected, allowing high current to flow through the patient whenever the patient formed a circuit to ground. Standards limiting current in any circuit are vital to prevent excessive heating of the power supply wires leading to fires.

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.