explaining the purpose of neutral wire?

ColJack · 11 Oct 2009

for the benefit of Goldberg..

hellmooth said:
question being.....
1. can someone explain the purpose (if thats the right word??) of the neutral wire in a circuit?

It's there as a return path for the current.

2. why does it have 0 volts?

It has 0 volts because voltage is relative to something, in this case earth, and the neutral is tied to earth.. in a generator that is not earthed then it is relative to the live, so you could say that it is at 240v with respect to the live.. or that the live is at 240V with respect to it.

3. my understanding was that it was a return for the current flowing from the live wire?

well it is and it isn't.. in AC, current flows both ways.. so you can't really say that it is FROM the live since on half the cycle it's feeding current TO the live..

4. if you touched the neutral side of a load under power would you get a shock?

it would depend on the length and size of the neutral back to the source..
as the neutral and earth are seperated at some point, they drift appart as the resistance increases..

5. if so how can it be 0 volts?

normally it's a short enough length from where it's earthed to not create much more than a small difference..

ColJack · 11 Oct 2009

hellmooth said:
wow thanks for all the information,much appreciated and helped clear it up somewhat

so when the current has been used by the load and returns through the neutral wire,finally being connected to earth back at substation,it is for want of a better word dissipated into the ground?it still has the same current going through it but the voltage is at near zero as its not being pushed with the same intensity?

voltage does the pushing..

think of it as a water pipe attatched to 2 upturned bottles half filled with water.

the height of the bottles is the voltage..
the size of the pipe is the resistance
the amount of water running through the pipe is the current..

with the bottles at the same height, the water doesn't move and each bottle is half full of water.

when you raise one bottle the water runs out of it and into the other..
if you then reverse which bottle is up and which is down then the water runs the other way and fills the other bottle..

if you only raise the bottle a little bit, the water runs slowly, if you raise it a lot it runs faster.

now.. if you put one bottle on a table ( earth ) and leave it there , then raise and lower the other one, that's what is happening with an earthed neutral..

Goldberg · 11 Oct 2009

ColJack said:
hellmooth said:

question being.....
1. can someone explain the purpose (if thats the right word??) of the neutral wire in a circuit?

Click to expand...

It's there as a return path for the current.

Quite so, but how did that benefit me?

2. why does it have 0 volts?

Click to expand...

It has 0 volts because voltage is relative to something, in this case earth, and the neutral is tied to earth.. in a generator that is not earthed then it is relative to the live, so you could say that it is at 240v with respect to the live.. or that the live is at 240V with respect to it.

The neutral in a generator supply isn't at 240V wrt the live. If anything it's at -240V.

ColJack · 11 Oct 2009

you asked why all the talk about neutral being tied to earth.. so I re-listed the OP's list of questions with better formatting..
I tried pointing out that it's only "0 volts" when referenced against earth if it's tied to earth at some point..

The neutral in a generator supply isn't at 240V wrt the live. If anything it's at -240V.

no it's not, and that's the point we've been trying to make to you..

there is no + or - when it comes to AC..
since the voltage is referenced to the other end of the coil, then when end A is "+" as you put it, the end B is "-".. then it reverses... so that A is "-" and B is "+"..

ban-all-sheds · 11 Oct 2009

Goldberg said:
The neutral in a generator supply isn't at 240V wrt the live. If anything it's at -240V.

It's at 240V wo line 100 times a second, and at -240V 100 times a second.

(Assuming a 50Hz sine-wave output of at least 170V RMS).

matt1e · 11 Oct 2009

Goldberg said:
RF Lighting said:

There is 0V on the neutral because it is tied to earth. This means that the neutral wire is physically connected into the ground with the use of earth rods and the like on he distribution network, and therefore, if you take a voltage reading between a neutral wire and earth, it shows 0V.

Click to expand...

So if you don't use 'mains' or a 'distribution network', and instead use a generator, and don't connect an earth to anything or connect anything to an earth, what is the purpose of the neutral connection?

Does it have a different purpose to the neutral in a 'mains' installation?

no

Goldberg said:
I'm open-mouthed to see the sheer number of words that people are writing about something so simple.

apparently not so simple for some eh

Goldberg said:
And if someone in their second year of studying hasn't already "got" what the neutral is, they should be barred from the building until they do, because it's completely impossible for them to be safe without that understanding.

Goldberg said:
matt1e said:

Goldberg said:

And why all this talk of the relationship between neutral and earth? It's a meaningless distraction.

Click to expand...

because the op asked

hellmooth said:

why does it have 0 volts?

Click to expand...

Click to expand...

Indeed he did, but the answer has nothing to do with earthing. Or an earth. Or the Earth.

or you still sure about this?

Goldberg said:
If you, or anyone, thinks that it does, then please explain the function of the neutral (or 'minus') connection in a circuit comprising a battery, a lamp, and two wires, all sitting on a rubber mat.

see above

matt1e said:
]now please explain to me and the op why there is 0v on the neutral as I have obviously been wrong in my assumptions so need to be corrected
so go on please enlighten us oh knowledgeable one
pretty please

i'm still waiting for your explanation
or do you give up?

Goldberg said:
The neutral in a generator supply isn't at 240V wrt the live. If anything it's at -240V

this gets better all the time I would stop making statements if I were you!
there's a saying about engaging your brain before putting your mouth in gear goldberg and also one about words coming back to haunt you and I'm sorry if it seems like I'm picking on you now but you did come in guns a blazing

or are Rf, Coljack and Ban all wrong too? and about to get some stick as well?

matt

Spark123 · 11 Oct 2009

Goldberg said:
If anyone thinks that discussion of the earth is relevant or essential, then please explain the function of the neutral path in the output from a generator.

Yes, as without it being bonded to earth it isn't neutral.
The function of the neutral path is to provide a return path for unballanced single or three phase loads. It is bonded to earth for safety, amongst other reasons which I covered before.

Goldberg · 11 Oct 2009

ban-all-sheds said:
(Assuming a 50Hz sine-wave output of at least 170V RMS).

Erm, isn't 240 the RMS figure, i.e. isn't the wave +340 to -340 peak-to-peak?

Spark123 · 11 Oct 2009

matt1e · 11 Oct 2009

I'll stick up for you ban

ban-all-sheds said:
It's at 240V wo line 100 times a second, and at -240V 100 times a second
(Assuming a 50Hz sine-wave output of at least 170V RMS).

correct statement
matt

ban-all-sheds · 11 Oct 2009

Goldberg said:
ban-all-sheds said:

(Assuming a 50Hz sine-wave output of at least 170V RMS).

Click to expand...

Erm, isn't 240 the RMS figure, i.e. isn't the wave +340 to -340 peak-to-peak?

Which RMS figure?

RMS figures are always positive.

Goldberg said:
The neutral in a generator supply isn't at 240V wrt the live. If anything it's at -240V.

So 240V can't be an RMS voltage.

An RMS voltage of 170 will give you peaks of ±240.4 volts, so 2 x +240V and 2 x -240V each cycle.

matt1e · 11 Oct 2009

but I agree on the uk mains figures too
or 325v @230v rms if you prefer to be more up to date
matt

Spark123 · 11 Oct 2009

Isn't that 1x 240v and 1x -240v per cycle? 50x each per second on a 50hz supply?

We use RMS as the average (mean) voltage of a sine wave over a cycle is zero.
If The RMS voltage is 240v, the peak voltage is about +340v and -340v giving a peak to peak voltage of about 680v.

properleckie · 11 Oct 2009

Come on fellas far too much testosterone around!
The OP asked a basic (too basic?) question which many of us have tried to answer in a variety of ways, unsuccessfully I think.
I would suggest he askes his tutor or one he can approach out of class and get a direct answer before we start trying to explain a site supplies transformer 230v primary , 110V [55-0-55v] CTE secondary.....

hellmooth · 11 Oct 2009

yeah seems to have gotten a bit heated over what was such a 'simple' question,doesn't seem that way now. and i dont think it is too basic,maybe the way i worded it made it look like i didnt know how a circuit works,i do but didnt totally understand why there was 0v at neutral end thats all,doesn't make me 'unsafe' at work!

thanks for all replies though,i do understand slightly better

being an adult trainee we dont get as much college time as say an apprentice,19 days a year to approx 70-80 days for an apprentice,so we have to do a lot of work out of college,hence me being on here

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

explaining the purpose of neutral wire?

Goldberg

Goldberg

Similar threads