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Can earth Short circuit?

by Godwin Kessy
Tags: circuit, earth
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Godwin Kessy
#1
Mar5-12, 05:48 AM
P: 91
Can a short circuit occur when a neutral wire is earthed, example a man touches a bare neural wire with bare hands..? And is the effect different for alternating and direct current?
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Averagesupernova
#2
Mar5-12, 12:32 PM
P: 2,513
In the U.S. the neutral is already connected to the earth with a ground rod at the transformer and at the service entrance of the building. So what do you think? DC doesn't really apply here does it?
Godwin Kessy
#3
Mar6-12, 12:10 AM
P: 91
I never thought i could not have any idea on this... What i know when the circuit is completed.. meaning the live connected to neutral.. Current flows whether it's dc or ac.. and earthing a device as i knew is only due to grounding the static charges that might result in the metallic parts of the device.. A challenge came up when a friend of mine just said that the body of the car works as neutral... Okay it's possible since it's a conductor but.... is it not going to be harmful? There is where the question arose...

psparky
#4
Mar6-12, 07:41 AM
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Can earth Short circuit?

Quote Quote by Godwin Kessy View Post
I never thought i could not have any idea on this... What i know when the circuit is completed.. meaning the live connected to neutral.. Current flows whether it's dc or ac.. and earthing a device as i knew is only due to grounding the static charges that might result in the metallic parts of the device.. A challenge came up when a friend of mine just said that the body of the car works as neutral... Okay it's possible since it's a conductor but.... is it not going to be harmful? There is where the question arose...
The frame of a car does act as ground. The negative terminal of the battery is connected to the frame of the car. It's been done this way for a hundred years. It's very convenient as ground is always available no matter where you are in the car.

It's not harmful, because if you do happen to touch hot and ground at the same time you feel 12 volts.....you feel essentially nothing unless you are soaking wet maybe.

All potential hots come from a fuse block as well. So in the case of a dead short....you simply get a blown fuse rather than a bunch of wiring on fire.
jim hardy
#5
Mar6-12, 09:29 AM
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Earth can be though of as just another wire that goes everywhere.

If it becomes part of your circuit, current can flow through it.

Sparky's automobile is separated from earth by the rubber tires which are very good insulators. So the only current likely to flow between a car battery and earth is that "static" charge you feel on cold dry winter days when exiting the vehicle.

"Ground" is an unfortunate term for circuit common because it infers earth.
Usually circuit common is not "earth" , though it can be tied to earth as it is in residential wiring..

old jim
psparky
#6
Mar6-12, 09:41 AM
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Quote Quote by jim hardy View Post
Earth can be though of as just another wire that goes everywhere.

If it becomes part of your circuit, current can flow through it.

Sparky's automobile is separated from earth by the rubber tires which are very good insulators. So the only current likely to flow between a car battery and earth is that "static" charge you feel on cold dry winter days when exiting the vehicle.
This is also why your automobile is one of the safest places to be during a lighting storm!
Averagesupernova
#7
Mar6-12, 09:53 AM
P: 2,513
Quote Quote by psparky View Post
This is also why your automobile is one of the safest places to be during a lighting storm!
The very short distance from the chassis to the ground is miniscule comparted the distance the lightning jumps from the sky so the rubber really doesn't do all that much. The reason the automobile is safe is because it forms a faraday cage.
psparky
#8
Mar6-12, 10:00 AM
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Quote Quote by Averagesupernova View Post
The very short distance from the chassis to the ground is miniscule comparted the distance the lightning jumps from the sky so the rubber really doesn't do all that much. The reason the automobile is safe is because it forms a faraday cage.
What's a Faraday cage?
Godwin Kessy
#9
Mar15-12, 02:46 AM
P: 91
Hallow guys so far am not satisfied at all.... I now realize i require a big concept that i ever had from you guys.... What I know earthing commonly means the return path for electric current, which is normally common... or can be grounding(connecting to the earth-planet)... Please guys get me here... the problem comes... can there be a flow of electric current between a a source(live wire) and grounding (earth-planet as have spoken at earlier).... And how is that possible while am sure the ground (earth) cant form a complete circuit with the source voltage(live wire)... By this challenge am saying that.... Earthing or having the home appliances grounded doesn't help when short circuiting occurs to the appliance... other wise the earth wire has been connected to the neutral to some place... Is any one getting me clearly??
And for that reason.. earthing is only valid for static charges and not the flow of current??
Any objection??
sophiecentaur
#10
Mar15-12, 07:01 AM
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The car body is metal - just like wire. Most / many auto electrical devices are fed with a single (+) wire and the return is via the car body (earth). The (black, often) lead from the battery is usually bolted to the chassis very close to the battery and takes all the return current.

Some devices have two wire feeds (+ and Earth). Many car body parts, these days, are plastic in which case, this is essential for equipment mounted on them.
The word 'neutral' is not used in DC circuits because it has a specific meaning for AC supplies.
Also, in your first post, you talk of a man 'shorting' to earth. People have much too high resistance to be able to provide a short circuit. Some current may flow - that's all.
Windadct
#11
Mar15-12, 09:57 AM
P: 564
Hello Godwin - I'll apologize for the car discussion working it's way into your thread - if I read neutral I am thinking of power system wiring - not a vehicle, but then your question about DC does not really apply ether.

A neutral SHOULD be considered an energized ( hazardous) conductor. In a household probably not so much of an issue but in larger systems - there can be neutral current, and the bonding point (back to earth / ground) may be far away or not have a good connection.

In your OP - you mention the "when a neutral wire is earthed" - they way you phrase this is a little concerning - the order of connections should be Ground then Neutral then Mains - If a device is energized ( connected to the power, even if turned off! ) and then you connect the neutral to ground- yes -you could be killed. If you touch a neutral - while standing on the ground - you can also suffer. You should not touch any energized connectors.


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