why normal current(not acces current) is not flow thrugh a earth wire.?

Question

in domestic electric circuit ,earth wire is used so that acces current in circuit can flow throuh it ,because it s resistence is less than a live and neutral wire.......then why normal current(not acces current) is not flow thrugh a earth wire.
as we know that,resistence of earth wire is less than live and neutral wire then current should flow in earth wire only.....but this is not happpen....

Answer 1

This depends on the local electrical code/regulations where you live. The multiple earth neutral system (MENS) used in Australia is shown below. Within the house the neutral current flows only in the neutral wire, and the ground current (due to leakage in an appliance) flows in the ground wire within the house. Note that there is a neutral and an active link in the distribution switchboard. Follow the path through from the transformer through a power outlet and back through the neutral, or through the protective ground for an active to ground leakage. RCD (residual current devices, not shown) supply groups of distribution breakers.



However neutral current flows between the houses and the supply transformer through both the neutral and the earth. Typical resistance of each path may be 0.6 ohms, but the earth impedance can rise in dry seasons, and the neutral can become faulty too. Generally everything keeps working safely with faulty ground or neutral, but there are specific issues. The ground conductor to the earth electrode might be thicker. Water pipes may be carrying significant current if the ground electrode is not effective, and especially if the neutral fails too... Plumbers know to beware of opening water pipe connections, just in case. They bypass the joint with a jumper lead. Each house has its own earth connection, except where unsuitable, e.g. house is on rocky ground etc. In that case an earth wire may be run back towards the supply transformer. Thus some houses might have a protective earth connection all the way back to the transformer.



This link explains different earthing systems, which have various pros and cons. It uses European terminology, where the MENS system is called TN-C-S I think. Note that only applies to the supply side of the house.

http://en.wikipedia.org/wiki/Earthing_system

Within the house I would think all countries are more or less similar, something like this, the basic concept for a single phase distribution.

http://electricaltechnology.org/2013/05/wiring-of-distribution-board-with-rcd.html

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Answer 2

I think you are in the UK, so a UK answer will be given.

The earth wire or Circuit Protective Conductor (CPC) is provided to all class 1 equipment and to any part of an installation that has a conductive enclosure which may, under specified fault conditions, become 'live'. The purpose of the CPC is to connect this metalwork to the general mass of earth and eventually back to the neutral of the supply transformer. This allows current to flow when an insulation breakdown happens, the resistance of the CPC will be larger than that of the phase or neutral but will be low enough to allow sufficient current to flow to ensure that the fuse blows or the CB trips within the specified time for that particular circuit. How do I know this, I used to teach qualified electricians to pass their 17th edition qualifications in Inspection and Testing.

Answer 3

Normal current can also flow through earth if you make it flow. But this is not a good practice. Earth wire is normally isolated from the circuit and wired as a protective Mechanism.

Answer 4

The safety ground wire holds the product body at zero volts, such as when there is a short or leakage in the device. If it were used as a neutral then a neutral break would put the product at hazardous voltage and shock the operator. The safety ground usually causes the breaker to trip and remove power from a product that has a fault.

Answer 5

Generally a neutral is far grounded wire ,and all the electricity it current with negative ion of the earth system.A ground wire it's a close grounded that it is secondary safe mode for fast return to ground any electrocution without making damage in rest of the current.

Answer 6

The load current is from line to neutral as the load is connected (or should be..) between line and neutral. the earth is there just to protect you... If load is connected from line to earth, then current is through this connection, no doubt. But this is what is called a fault, and is never done. However faults do develop and in such a case, a resistance ( leakage) may exist between line and earth, though it should be inifinity normally. In such a case, a current does flow through that resistance, as the supplier of electric power has connected neutral to earth on his source side. the earth you generally have in domestic connections is a safety earth, and is connected to mother earth through a low resistance earthing.

It may be useful to read through the chapter on ac in Rizzonis' principles of electrical engg. Consider a 230watt load connected from line to neutral. current through that is 1 amp. If it is enlosed ina metal container and the container is earthed, there is no current in the earth line. Over a period for unknown reasons, a leakage of 100k develops, from the 230watt load to the enclosure. If this fault is near the line, the current through 100k will be about 2.3 mA. If this fault is near neutral, the current may be much smaller as voltage of neutral witth respect to earth is small (say < 3V). Thus you have a max leakage current of 2.3mA. this current can be sensed and used to trip the supply as is done in earth leakage detection devices.

Answer 7

For a pictorial, in addition to a verbal explanation, have a look at this http://www.davidbridgen.com/leakage.htm