CrazyEngineers Archive
Old, but evergreen and popular discussions on CrazyEngineers, presented to you in read-only mode.
@mvaa07 • 25 Apr, 2010 • 1 like
we've been taught that ac current is alternating in nature i.e. no negative or positive poles but we been also told that live actually carries the current and the neutral takes it back this way live should be treated as the positive pole and the neutral the negative which is pretty much contradictory ............. please help
@sauravgoswami • 25 Apr, 2010 Neutral wires do not carry any charge, as both positive and negative charge is present they cancel each other out,but neutral cannot be treated as ground although it behaves as ground, live wires carry charge whether negative or positive.
@mvaa07 • 13 May, 2010 thanks for the reply but i m not getting that thing into my brain its just maths all over not the correct physical meaning , i would really appreciate if you can please explain in detail ......................................thanks again
@aj_onduty • 26 Aug, 2010 • 1 like Basically, to understand what a live and a neutral is, you should first know a few things. Let me explain them.
Electrical energy is generated in a generator as three phase. Now, a three phase power has no neutral, theoritically, as it is considered balanced in the theoritical point of view. But we cannot create a practically balanced 3phase supply. We use a neutral to compensate the imbalance. Now, in a single phase supply, we take one phase from the three phases and use it. If we take it seperately, there is no guarantee that it may be balanced, as we cannot co-ordinate the usage of the consumers using the power in different phases. So, there should be a neutral provided which is grounded. This neutral compensates the imbalances between the three phases. It is not a negative of your supply. In the same live wire itself, we get the positive and negative. The live wirechanges the polarity every 1/100th of a second(for a 50Hz supply). when we connect it to the neutral, the neutral becomes positive and negative according th the polarity of the live wire every 1/100 th of a second.
I think you understand what I am trying to say. Please let me know if I am wrong.
Thank you...
@shreyasm89 • 01 Sep, 2010 @aj-onduty-What do you mean by compensating for the imbalance in the 3-phase?Do you compensate for the 60 deg. phase shift? pls enlighten.
@aj_onduty • 01 Sep, 2010
shreyasm89
@aj-onduty-What do you mean by compensating for the imbalance in the 3-phase?Do you compensate for the 60 deg. phase shift? please enlighten.
I am sorry for confusing you with phase lag/lead with load imbalance. Here, I meant to say that in some systems(I am specifying distribution systems which deal with multiple single phase output and a 3phase input), one phase may draw more power from the supply than the other phase. This imbalance is countered using neutral.
@arm1368 • 01 Sep, 2010 excuse me, my language is not good
in electrical concepts, Potential difference (voltage) is important in power supply and not Potential.
in ac or dc , current flows from positive polarity(larger potential) to negative polarity(fewer potential) and difference between them (two potential) is important .
following power supply are equal:
-(negative polarity): -6 , +: +6
- : 0 , +: +12
but second power supply is better because negative polarity is 0 and we can use ground.
(ground potential is 0 optional)
@aj_onduty • 01 Sep, 2010 Dear arm1368,
I believe that you have confused yourself with the properties of AC and DC. Kindly do a search of how power generation in AC is done and the working of an alternator. May be your query will be answered.
If still your doubt isn't clarified, We will help you.
Thank you for asking.Keep on asking questions. We are happy to help.
@bill190 • 01 Sep, 2010 • 1 like A neutral is on a transformer secondary/output and is the "center" wire.

So the output of the transformer is hot wire, neutral in center, and hot wire.

In the U.S, the voltage between the two hots is 240 volts AC. Between a hot and the neutral is 120 volts AC.

The neutral is in the middle!

Now imagine you have a room with two windows and a door.
Imagine each window is a hot and the door is a neutral.

One window has a fan blowing air in. Another window has a fan sucking air out. (Same amount of air)
No air goes through the door!

Now close one window, then air now flows through the door!

Same with a neutral and two hots single phase. If an equal amount of electricity is being used on each hot, then no current will flow on the neutral.

Use electricity from just one hot, then the same amount of current will flow through the neutral.
@aj_onduty • 01 Sep, 2010 In the US, the nominal voltage is 120V, supplied at 60Hz. This is the voltage per phase. This means that the line voltage, that is, the voltage between two lines will be 240V, as told by bill190(hot wires). This means that in the US, we supply two phase power which can be used accordingly by the user for 120V or 240V. Am I correct? please let me know. Kindly note that this is just an assumption of mine and I need corrections, if any so that I can have a good answer about the concept of live and neutral.
Thank you for your effprts.
@arm1368 • 02 Sep, 2010 thank you
it is useful.
@shreyasm89 • 12 Sep, 2010 thanks aj. But how does the neutral provide equitable distribution of power?
@aj_onduty • 12 Sep, 2010
shreyasm89
thanks aj. But how does the neutral provide equitable distribution of power?
Suppose we have three pipes which are enclosed in a large pipe. One side of these pipes are connected to a large reciprocating pump which an supply water to three pipes. But it can only supply a fixed amount of water. These three pipes' ends are nozzle shaped. The nozzles let only a limited amount of water out. Suppose one of these nozzles are blocked partially. The pressure in the pipe increases. So, the water pressure through the other pipes also increase. Now, this can cause bursting of pipes. To minimize this, we have a pressure release valve fitted to each pipe which lets some water out from the pressurised pipes, lgiving safety. The water released by the valves go back to the reservoir through the large pipe in which we have enclosed the other pipes.
Now, consider the three pipes as R,Y and B in transmission and the enclosing pipes as neutral. I think you got the idea.
If you are confused, let me know.
Thank you.
@shreyasm89 • 14 Sep, 2010 So you mean to say in a 3-phase systen there will be a single neutral which will compensate for the surge in current. But from what I know neutral is supposed to be the return path for the phase curent. Forgive my incompetence but I am really confused with this. I am currently looking for it on the net.
@praba230890 • 24 Sep, 2010 Does A.C current changes the direction of flow in each cycle?......plz explain me abt the change in polarities in A.C
@dheerajkvs • 24 Sep, 2010 Live and Neutral wires have their own significance.
Both of them combined contribute to the flow of energy.Live wire carries the charges and the neutral provides the way for the charges to move back to the source.It is like a cycle as current is due to the flow of charges neutral provides the path for the charges to continue the cycle.It is like two semi circles joined to form a circle so that the path is complete.

It also balances the changes in the current in a 3 phase system.

Please correct me if i am wrong.
@mvaa07 • 18 Oct, 2010 thanks bill190 .................. got little bit idea about that!!!!!!!!!!
@Munguti • 25 Oct, 2010
mvaa07
we've been taught that ac current is alternating in nature i.e. no negative or positive poles but we been also told that live actually carries the current and the neutral takes it back this way live should be treated as the positive pole and the neutral the negative which is pretty much contradictory ............. please help
There is no such thing as a positive pole in AC and you should not even think of it as such. Remember for non earthed ac equipment, were there are two pins one for live and the other for neutral, there is no specific way for plugging your two pins into the socket infact there are both the same , this is different for earthed equipment because of the earth connection and the 3 pin configuration. If polarity mattered we would have a specific pin for negative and another for positive and if you connect it wrongly them it doesnt not work just as with batteries in a torch with incorrect polarity.
@pinky singh • 01 Sep, 2015 Does live wire only positive charges or protons and neutral wire only negative charge....???
What is the use of neutral wire in domestic electric circuits....???
@vamsi kancharla • 02 Oct, 2015 if the supply is balanced current flowing through neutral is 0
practically no load is balanced the present p.s is unbalanced one so neutral carry some current the neutral will have the voltage of 0.1-0.3 volts in practical
comming to single phase supply if the generator is a single phase generator (not used now a days) in power station the neutal is grounded so the neutral voltage is 0 so as we know that current flows from high potential to lower potential so current flows from phase to neutral
@lal • 04 Oct, 2015
vamsi kancharla
current flows from high potential to lower potential so current flows from phase to neutral
Half of that is true "Current flows from higher to lower potential", but it doesn't flow from phase to neutral alone! Current flows both ways in an AC power system, that is from phase to neutral and vice versa.

If you check the waveform of voltage in a 230V, 50Hz AC power system, you could see the polarity changes alternately hundred times in a second to positive and negative maxima. The reference here is ground potential - Zero Volts (and hence neutral potential as neutral is grounded).

From the voltage waveform: For the positive half cycle, potential of "phase" or "line" or "live wire" is above ground (and hence above neutral potential too). Conventional current during the positive half cycle would now be flowing from phase to neutral (assuming potential is applied across a pure resistive load). For the negative half cycle, potential of phase is actually below ground and hence below neutral. During this condition, neutral is at a higher potential than the phase as phase potential is negative when compared to ground. Conventional current flows from neutral to phase during the negative half cycle.

"So current flows in both directions in an AC circuit. The change in direction of conventional current flow is twice that of supply frequency." This is the reason, analogue ammeters used in AC systems are of PMMI type. If a PMMC instrument (used in DC circuits) is used, the needle could be seen fluctuating in both the directions at the same rate as that of frequency, but limited by the inertia of the movement.

It doesn't actually make sense if phase and neutral connections are reversed in an AC system, as the potential and current are alternating periodically. But, doing so would expose various circuit components and nodes to be at higher potential even when the switch is off, which is not preferred as that is actually dangerous. This situation can be solved if a DPST switch is used to power the devices. But almost all household components are controlled by SPST switches.
@1NAVEEN MANIVANNAN • 29 Feb, 2016 pls tell me does live wire carrired positive or negative charge??and pls tell me about live,neutral,earthing
@Praveenpe96 • 14 Feb, 2018
aj_onduty
Basically, to understand what a live and a neutral is, you should first know a few things. Let me explain them.
Electrical energy is generated in a generator as three phase. Now, a three phase power has no neutral, theoritically, as it is considered balanced in the theoritical point of view. But we cannot create a practically balanced 3phase supply. We use a neutral to compensate the imbalance. Now, in a single phase supply, we take one phase from the three phases and use it. If we take it seperately, there is no guarantee that it may be balanced, as we cannot co-ordinate the usage of the consumers using the power in different phases. So, there should be a neutral provided which is grounded. This neutral compensates the imbalances between the three phases. It is not a negative of your supply. In the same live wire itself, we get the positive and negative. The live wirechanges the polarity every 1/100th of a second(for a 50Hz supply). when we connect it to the neutral, the neutral becomes positive and negative according th the polarity of the live wire every 1/100 th of a second.
I think you understand what I am trying to say. Please let me know if I am wrong.
Thank you...
Hello bro ... I just want to know one thing the AC voltage is in alternating nature and it changing the electrons flow in 50 cycle ( one positive polarity and one negative polarity is called a one cycle) in a second and u said that an 1/2 cycles phase wire producing electrons and another 1/2 cycles the direction changes in a second that the electrons flow through neutral wire in half cycle then why I won't get any shock while touching the neutral wire when the electronics flows in every half cycle pls whether it's correct or not just prove the flow of electrons directions.
@STI Web • 06 Mar, 2018 The live wire carries current to the appliance at a high voltage. The neutral wire completes the circuit and carries current away from the appliance. The third wire, called the earth wire (green/yellow) is a safety wire and connects the metal case of the appliance to the earth. Use Accelerometer Mounting and Accelerometers.
@STI Web • 15 Mar, 2018 All neutral wires of the same earthed (grounded) electrical system should have the same electrical potential because they are all connected through the system ground. Transmitters and Monitors. Neutral conductors are usually insulated for the same voltage as the line conductors, with interesting exceptions.

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