Explain the Neutral???

[cross]

I am seeking some clarification on what the neutral actually does...

I have heard the neutral is considered to be at zero volts.

I have also heard that the neutral carries current back to the source, therefore completing the circuit.

If this is true, how does the current travel along the neutral if there is no voltage forcing it along??

thanks in advanced.

 

[mapj1]

The end of the neutral at the substation is at zero volts, and the wire is a good conductor, so the end at your house is only a few volts higher than this. In the same way the live voltage (at your end) is a smidge less than at the transformer end. These two lost voltages are the 'line loss'. In practice most of the 230V is accross the appliences in your house, as they have a far higher resitance than the feed lines. This is also why a short circuit is so dangerous, as then the only resistance limiting the current is that of the supply lines, and a very large current thousands of amps, will flow until something (hopefully a fuse or a trip, and not the wire you are holding) opens the circuit.
hoep that is noddy enough, regards M.

 

[felix]

All the current running out of the live wire into a lightbulb/motor/heater/whatever, has to come out again. That, in a nutshell, is what the neutral wire is for.

To call it neutral is a bit of a misnomer since this implies that it just sits there doing nothing. It differs from the live wire only in as much as, in the absence of any wiring faults, it won't throw you across the room if you touch it. DON'T TRY THIS!

 

[bathjobby]

Potential difference between live and neutral is 230V, so the live is at 230V+ to the neutral and the neutral is at 230v- to the live. This difference causes electron to flow i.e. current. In theory you could run the live at 430v+ and the neutral at 200v+ (relative to ground 0v) and maintain the potential difference, relatively......
But if you had to ask in the first place, I'm guessing you won't 'get this' !

 

[ban-all-sheds]

Potential difference between live and neutral is 230V, so the live is at 230V+ to the neutral and the neutral is at 230v- to the live.

Err - we have an alternating supply, so the potential difference between the live and the neutral varies from +230V to -230V 50 times a second (RMS values - the actual values are ±325V).

 

[bathjobby]

Yep, theory holds true even at RMS = 1.47, so what was the point you were making ?

 

[ban-all-sheds]

Well - the only point I was making was to help Cross, not score any off you - if he's come here for some Electrics 101 I thought it was important to clarify "the live is at 230V+ to the neutral and the neutral is at 230v- to the live", since the +/- relationship changes 50 times a second...

PS - Peak:RMS for a sine wave is (to 4 DP) 1.4142, not 1.47.

 

[bathjobby]

Good, but given that your plunge into that level of detail did nothing to clarify the original posters question nor my response, looks like a hurt ego also !

 

[bonebill]

I am seeking some clarification on what the neutral actually does...

I have heard the neutral is considered to be at zero volts.

I have also heard that the neutral carries current back to the source, therefore completing the circuit.

If this is true, how does the current travel along the neutral if there is no voltage forcing it along??

Current travels along a conductor because there is a potential difference between the two ends of the conductor.

In the case of conductors used to supply power, this potential difference will be very small.

When you say "the neutral is considered to be at zero volts", the "zero volts" to which you are referring is the potential difference relative to earth.

In fact, whenever there is a current flowing in a conductor, it does not have one single potential; there will be a potential gradient along the conductor. This can be measured as a potential difference between the two ends of the conductor.

The end of the neutral conductor at the substation may well be at zero volts relative to earth.

However if there is any current flowing in the circuit, then at any other point on the neutral conductor the potential will be non-zero.

Consider the live and neutral conductors between the substation and your house.

Say they have a resistance of 0.1 ohms.
Say the supply voltage is 232 volts at the substation.
Say your house is drawing 10 amperes.

According to Ohm's law, the potential difference is equal to the product of the current and the resistance.

Any current flowing through one conductor will be matched by an equal and opposite current flow in the other conductor.

So each of the supply conductors will have a potential difference between the ends of 10 x 0.1 = 1 volt.

It is this 1 volt potential difference between the ends of the conductor that drives the current through it.

Both the live and neutral conductors are in the same situation; they have the same potential difference across them, so current is driven through them in the same way.

Considering the neutral conductor, the end at the substation will be at zero volts relative to earth, but the end at your house will be at one volt relative to earth.

Similarly for the live conductor, the end at the substation will be at 232 volts relative to earth, but the end at your house will be at 231 volts relative to earth.

The "supply voltage" as measured at your house will be the potential difference at the house which will be the expected 230 volts.

(As you can see, the "voltage" at the house will be dependent on the current being drawn, and the resistance of the supply cables. The current will vary according to demand, and the resistance will vary according to the distance between any given house and the substation. So pretty much everyone will see a different "supply voltage" and it will also vary between different times of day.)

 

[Damocles]

I think it a pretty important point that we are talking about AC and the live wire alternates between +230 and -230V. Also important that we are talking about RMS voltage (average voltage), not peak voltage. This important little fact means that if you stick your fingers inside your telly the rectified AC may have turned into 400V DC. If you tried measuring something connected to mains with a meter only rated up to say 300V DC, you should not be too surprised if it went bang when you put 240V AC into it.

This entertaining fact also means that if you were quick enough it would be possible to grab the the live and neutral just at the point when the live line is changing from + to -, and is zero. Just make sure you dropped it again pretty quick too. (do not try this at home!)

The AC starts out as a votage difference between two wire coming out of a generator or transformer. The voltage on either wire looks exactly the same as on the other one. The only difference is that one of them is then connected to ground and called 'neutral', while the other is left floating and is called 'live'.

Short them out and either the generator catches fire or stops dead.

 

[AdamW]

PS - Peak:RMS for a sine wave is (to 4 DP) 1.4142, not 1.47.

I prefer to just use 2^0.5

 

[uselessFCUK]

Potential difference between live and neutral is 230V, so the live is at 230V+ to the neutral and the neutral is at 230v- to the live.

Err - we have an alternating supply, so the potential difference between the live and the neutral varies from +230V to -230V 50 times a second (RMS values - the actual values are ±325V).

Bathjobby has a point in his reply to your quote. It's all about attitude. Would this be your reply in a pub, face to face. Hmmm...possibly not. Does us all a favour, be polite and positive in your interesting and helpful replies. You are obviously a knowledgable guy with lots to tell, stay on our level and share it constructively. Your talent speaks volumes whereas a minority of your responses makes you look arrogant. Be good, for ****s sake.

 

[Damocles]

The current is AC, like the voltage. Which means that all the electrons rush off in one direction, and then rush back the other way. And only a very very smalll distance. So you are stuck with the same ones you started with.

 

[ban-all-sheds]

Potential difference between live and neutral is 230V, so the live is at 230V+ to the neutral and the neutral is at 230v- to the live.

Err - we have an alternating supply, so the potential difference between the live and the neutral varies from +230V to -230V 50 times a second (RMS values - the actual values are ±325V).

Bathjobby has a point in his reply to your quote. It's all about attitude.

Indeed, but I can't help concluding that the one with an attitude problem is him, not me...

Would this be your reply in a pub, face to face. Hmmm...possibly not.

Absolutely - why on earth not? I didn't say "Err - we have...., you dork", or "Don't be stupid, we have....", I simply stated a fact with no derogatory phrasing whatsoever. Try reading it out aloud, in a tone of voice and manner which is not sarcastic or patronising or whatever - just a normal, conversational, neutral way, and see if you still think it was showing an "attitude"...

Does us all a favour, be polite and positive in your interesting and helpful replies.

Please tell me which part of my response was either impolite or negative.

Your talent speaks volumes whereas a minority of your responses makes you look arrogant. Be good, for ****s sake.

I was good. Bathjobby said that live is at 230V+ to the neutral. This is wrong, is it not? Or at best only half-right? So I wrote a correction. How can it be wrong to correct misinformation being given to someone asking a question?

 

[ban-all-sheds]

The current is AC, like the voltage. Which means that all the electrons rush off in one direction, and then rush back the other way. And only a very very smalll distance. So you are stuck with the same ones you started with.

I'm uncertain about that.