Basic Electricity: What is Neutral Wire & Why We Need It

[davenn]

have a look at these links

first one about the electron volt ( eV)

https://en.wikipedia.org/wiki/Electronvolt

and this one on the electric field and the movement of charge

http://www.physicsclassroom.com/class/circuits/Lesson-1/Electric-Field-and-the-Movement-of-Chargecheers
Dave

 

[jaus tail]

an analogy would be water flowing through a pipe in a rectangular circuit. and in the pipe there are turbines that the flowing water must move. there is a pump at one end.

now you have only limited water in the pipe. the voltage source is the pump while the resistance is the turbine. the pump will push the water to the turbine. the turbine will move. if the turbine is very rigid/heavy then it won't move and the water will be blocked. as in the water won't move ahead, go back to the pump.

if i increase the pump power, then the pump will push the water at more speed n force, this water will move the turbine n the water will continue to flow at reduced speed, then return to the pump. the pump will again push this water, which will again move the turbines, which will again allow water to move ahead n return to pump.

if i add more turbines, I'm adding more resistance. in this case the pump needs to be stronger/voltage source needs to be of higher voltage. current can be compared to the speed with which the water flows which reduces as i add more turbines.

 

[Bringitondown]

Hi Folks,

Didn't know what other thread to ask this on.

I have an electrical power eng book which keeps referring to negative current with respect to thyristors. Am I missing something here, is there such a thing. Current always flows from high to low potential. So if your terminal voltage is reversed to allow current to flow in the other direction, it is still a positive current flow?thanks

Any suggestions.

 

[davenn]

Hi Folks,

Didn't know what other thread to ask this on.

I have an electrical power eng book which keeps referring to negative current with respect to thyristors. Am I missing something here, is there such a thing. Current always flows from high to low potential. So if your terminal voltage is reversed to allow current to flow in the other direction, it is still a positive current flow?thanks

Any suggestions.

start a new thread of your own with the above Q, rather than hijacking some one elses thread
then we can get this post of yours removed

thanks lots

Dave

 

[Bringitondown]

No bother tadger, feel free

 

[sophiecentaur]

This thread has drifted every which way. To return to the OP and 'neutral'. In a domestic situation, the Neutral is merely one of two wires which go to a device and carry the current. (equal currents because they are the only paths used). Using a Neutral, rather than two equal status wires, makes no difference in most respects. No one would ever use (knowingly) the Earth conductor as a 'return' wire. As has been mentioned, it's a safety measure and carries no power.
Unfortunately, the situation with three phase distribution was introduced to the thread. That is very very different and adds loads of possible confusion. The HV system is connected to the consumer via a Transformer and there is no 'current' connection (no electrical path) between your kettle and the generator. The function of a Three Phase Neutral is totally different from the neutral in your home. To get into the complexities of the ways that three phase supplies can be distributed involves a whole gear change and the domestic wiring system should be sorted out way before three phases are tackled.
IN matters of EE, 'one step at a time' is the way forward.

 

[MidiMagic]

The equipment grounding conductors (safety grounds) must bond everything metal together and to the Earth ground and the neutral, but they must also be connected so that current does not normally flow through them. The current flowing though them in the event of a ground fault is needed to trip the circuit breaker.

Because the Earth ground is not low impedance, grounds to the Earth must be installed periodically. The neutral is solidly connected to the entire electrical system, and must be connected to the Earth with ground stakes at the following points (and only the following points):

1. The generating station
2. Every transformer
3. Every power pole
4. Every service entrance electricity usage meter
5. Every main power distribution panel at a service entrance

All equipment protective grounds must be kept separate from the neutral conductors at all points except the service entrance power distribution panel. At only that point, all of the neutrals are tied to all of the equipment grounds. Examples of the dangers of interconnecting neutrals and equipment grounds at points other than at the service entrance include:

- Years ago, people used to connect the equipment ground to the neutral at the load to save wire. The problem is, if the neutral wire breaks at any point in the circuit, the metal case of the equipment is now energized at line voltage.

- When an outbuilding is connected to a service in another building, the neutral must be kept separate from the equipment ground because current flows through the neutral. The equipment ground must be connected to the panel, and the panel must be bonded to all substantial building parts and a ground stake at the outbuilding. Otherwise, a shock could occur between a concrete pad at Earth ground and the shell of a metal power tool.

- Even such innocuous-looking items as water pipes, metal fences, downspouts, and posts should be bonded to the equipment ground at the service entrance.if there is a chance of someone coming into contact with both the electrical equipment ground and one of these other items. The death of a child a few years ago emphasizes this need:

The child was playing in a city park and touched a streetlight pole and a metal fence at the same time. The streetlight pole was connected to the equipment ground of the power system supplying the streetlight. The metal fence was driven into the ground, but not bonded to the power system supplying the streetlight. At just the tine the child touched both the streetlight pole and the fence, a ground fault occurred in a 12 KV feeder several miles away The massive current flow before the overcurrent devices shut down the feeder raided the equipment ground above Earth ground by about 1000 volts. So a potential difference of about 1000 volts existed between the power pole and the fence connected to the earth. Enough current flowed to kill the child.

If the fence had been bonded to the streetlight pole equipment ground, there would have been no voltage between these items.

The entire purpose of the equipment ground is to prevent voltage differences between different grounded items. For it to function correctly, no current must be allowed to flow through the equipment ground unless a ground fault occurs.

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-

 

[Russell Ensslin]

I thought the purpose of the effective growing fault current path was to allow the short to cause the over-current device to trip the circuit.
I suppose it would also keep the majority of the current to flow to the easiest path back to the source which would cause an imbalance from some less effective path and the moats effective path and ZAP! The child is dead. :-(

Is that what happened?

 

[MidiMagic]

There is one purpose for the grounding system and another purpose for the bonding system.

The equipment ground is there to cause the overcurrent device to trip. It does trip, but it takes time for this to happen. During this brief time, the equipment ground of part of the system is not at ground potential.

Bonding metal objects to the equipment ground makes sure that the electrical potential of every metal or conductive object in the area is at the same potential, relative to each other. Even if the ground potential as a whole changes, all of the metal objects change by the same amount. You can safely touch any two bonded objects at the same time without receiving a shock.

 

[Russell Ensslin]

Thank you midiMag;
I thought that the equipment grounding was the bonding to the ground fault current path to trip the breaker.

 

[davenn]

I thought that the equipment grounding was the bonding to the ground fault current path to trip the breaker.

Yes, that's the purpose