Why Do We Not Get A Shock From The Neutral Conductor?

[NozSpark]

Best not :innocent

 

[Apache]

well you learn something new everyday.... it goes +ve then -ve 50 times a second..... wow Thats what them ozzy rockers were on about all this time....

I gave this a little thought and think it goes +ve 25 times per second and -ve 25 times per second.................

 

[andrewedwardjudd]

have tried sensible replies and sarcasm and he still goes on and on and on..... just thought I'd throw my 2p worth (and thats all its worth) in. I remember installing a massive battery and generator system in an exchange and no I didnt try it but reckoned I would have felt something uncomfortable had I touched the -ve at the battery. But don't lets go off at a tangent this thread is bad enough as it is!

I am surprised that you are directing this at me. Some of the other replies made on this thread show a general lack of understanding from people who say they are qualified.

I came here to learn something. Evidently i also know something too.

 

[andrewedwardjudd]

TBH I was trying to keep it simple or this guy'll tie himself up in knots (unless he's a troll that is)

Evidently the subject is sufficiently complicated that many electrically qualified people do not understand what appear to be simple electrical principles. Your comment is totally unjustified

 

[andrewedwardjudd]

I gave this a little thought and think it goes +ve 25 times per second and -ve 25 times per second.................

It is 50 cycles rather than 50 half cycles

 

[steptoe]

The beginning idea of the thread was to resolve the nature of the neutral and find out why we get shocked by a live so that unquestionably I know the answer. My theory about the shock pathway going via air seems to have been debunked, but i was still wanting to know why the live was hot

In my own mind i am beginning to be satisfied i know what is happening

The variations on wiring a house are not important.

In the UK NZ and Finland, neutral is grounded and thus there is an easily available potential circuit which can be completed via your body if you touch 'live' even if you do not directly touch neutral to form a circuit.

In either country if you touch neutral there is no easily available circuit that be completed to form a circuit back to the substation.

but not always outside of the substation,

there are a lot of mad assumptions being stated in this thread,

you really really need to understand that the differing earthing systems in use in each country make a massive difference to how the neutral reacts in any given situation.

 

[andrewedwardjudd]

but not always outside of the substation,

there are a lot of mad assumptions being stated in this thread,

you really really need to understand that the differing earthing systems in use in each country make a massive difference to how the neutral reacts in any given situation.

I was asking for a fairly simple explanation for a typical functioning mains system. I said at some point that the earth and the neutral were effectively the same thing and said many posters were labouring the flow of current via earth.

My view, since i started this thread, is that all a person needs to understand is that we can get a lethal shock because an electrical circuit involving neutral is produced by design to enable a current flow like that. But no such design is available for neutral to connect to live.

What part is mad? What part really really needs to be understood?

 

[steptoe]

in a typical NZ situation the neutral is NOT the same as the earth, even though they may be connected, they perform different functions,

both myself and the REV have worked in NZ and understand the differences between the system commonly used there and the more common systems in use in the UK,

they are different cables with different functions.

yes, a neutral cable can produce a lethal shock, that is why it is classed as a LIVE cable under UK regulations.

 

[revjames]

draw a line and wind your neck in

 

[SPECIAL LOCATION]

Hi I was having a go at explaining grounding and after some discussion and a few arguments I came up against some problems because the internet was providing what appeared to be a totally wrong conceptualisation of the nature of our supplied power supply.

The internet is full of idiots spouting gibberish, so this statement is correct.

Ie many professional electricians are talking about an electrical flow to ground or neutral. That must be conceptually wrong since we are talking about alternating current?

Direction of current flow is irrelevant, you are asking about shocks. A sufficiently large DC supply can give you a shock whichever way round you connect two parts of your body. AC will give shocks on either half of the cycle. But in both cases you need a suitably high potential difference between two sources for a current to flow. e.g. 50v AC pd will give a shock but is considered a maximum limit not to be exceeded during fault conditions prior to disconnection of the supply.

As far as I can see we do not get a shock from a properly wired neutral or earth because the surface area of the so called live conductors exposed to air is very small compared to the very much larger surface area of the so called neutral/earth bonded conductors that is exposed to the air?

An example of the internet full of idiots spouting gibberish! Surface area is irrelevant. Potential difference between two simultaneously accessible points is the cause. If Neutral and Earth are at the same potential.. There is NO pd.

So in an unusual situation where the neutral was not connected to earth at your location, and the property was some distance to any other grounded neutral or it was unusually dry, and there was a large appliance with a live unpainted chassis or unbonded live sink that was near you, it seems to me you would get a shock if you touched neutral?

Your question only says the neutral not connected to earth at the load end. one has to assume that the supply is still connected correctly? Or in your unusual situation the property owner would have found none of their appliances were working as the circuit is not complete. Other than that, any time you split open any part of a circuit Line or Neutral there will be one live conductor (line or neutral) with a higher potential to the other half of the break in the conductor, thus a risk of shock. Which is why the Neutral IS a LIVE conductor.

I am right or am I talking rubbish?

Cheers

Andrew

My comments in red...

Primarily for any students who may be reading this posts

As you answered your own question on the first post..

yes you are talking rubbish.!

No further comments

:shakehead

:coat

 

[andrewedwardjudd]

My comments in red...

Primarily for any students who may be reading this posts

As you answered your own question on the first post..

yes you are talking rubbish.!

No further comments

:shakehead

:coat

I agree.

However i came here to get knowledge so i was in a position to have a conversation with another person without relying on the gibberish that electricians were providing on the internet.

Since i have perservered here i have been able to work out for myself what i can rely upon and what i cannot, or what is not needed for my purposes. Had i ran away I would not have learnt very much.

It is all good so far for me. I learnt something I did not know.

I note I can get a significant signal from a simple testing screwdriver if i jump into the air so I am still not entirely satisfied i cannot get a shock from for example humid air in a bathroom. Also as regards some electrians standing on insulated mats with boots to show apprentices they are not shocked it must be true that each person has a different ability to conduct electricity via their skin and even their internal electrolytes etc, where some skin types are noticeably much more oily or moist or prone to sweating than others and a drier person who habitually does not drink sufficient water will be more salty and be a better internal conductor but perhaps a poorer external conductor. It could be quite complex. I do not know.

Anyway......

The main area of confusion for me was the nature of the neutral where common sense suggested it must be like live, but i was not able to convince myself that the planet earth itself did not have some special quality.

As far as i can see, neutral is live with respect to live and the earth itself has so special function other than being common to neutral.

If you are again able to comment in read it would help me and who knows maybe it might help others.

 

[steptoe]

Earth is NOT common to neutral

when will you stop saying it is?

This is where you are fumdamentaly wrong, it is all dependant on the distribution system as to how earth and neutral relate to each other.

 

[SPECIAL LOCATION]

I note I can get a significant signal from a simple testing screwdriver if i jump into the air so I am still not entirely satisfied i cannot get a shock from for example humid air in a bathroom. Also as regards some electrians standing on insulated mats with boots to show apprentices they are not shocked it must be true that each person has a different ability to conduct electricity via their skin and even their internal electrolytes etc, where some skin types are noticeably much more oily or moist or prone to sweating than others and a drier person who habitually does not drink sufficient water will be more salty and be a better internal conductor but perhaps a poorer external conductor. It could be quite complex. I do not know.

Sufficiently large potentials and you can get a shock across almost anything....

But perhaps you have not heard or seen thunder and lightening.... :C

e.g.

Air, Clouds, Ground, Earth, Bodies..etc.. etc.. etc..

can all conduct electricity when big enough potential is present....

You could stand barefoot on a grassy hill with a metal umbrella in the next thunderstorm to test it for us if you want?

I have no idea what sort of electrical generating equipment you have in your bathroom..

or how long you spend in the shower...

But under normal circumstances your humid bathroom is again talking gibberish.

Earth only has some relevance when some part of a supply system is connected or bonded to the mass of earth somewhere....

A transportable electric generator mounted on a rubber wheeled trailer with no connection to the physical ground would have no bearing to earth from either line or neutral..

Neutral itself is primarily for the unbalanced currents from the three phase lines. L1, L2, L3.

In a fully balanced 3 phase system all currents are going up and down the Line conductors,...

NO neutral current!

In unbalanced system some current comes along the neutral conductor....

{e.g. a single phase off a 3 phase generated supply.}

If it was decided not to bond any part of this system to the mass of earth it would be dam near impossible to predict what potential difference could occur between conductive parts and earth itself, until such point as hazardous voltage exists..

Which is why the logical place to reference to the mass of earth is the star point, where neutral and all the phases come together..

As this will keep voltages with respect to earth to a minimum..

But other than that ..

As Steptoe says...

Earth and Neutral carry no direct relevance to each other any more than the earth reference did with early single wire telegraphy, morse code sets, or a telephone DC supply bonded one leg to earth.

For some obscure reason the questions keep shooting of onto irrelevant tangents...

rather like trying to compare a horse and cart with a petrol engine van!

Other than they are both means of transport they are unrelated to each other!

 

[andrewedwardjudd]

Earth is NOT common to neutral

when will you stop saying it is?

This is where you are fumdamentaly wrong, it is all dependant on the distribution system as to how earth and neutral relate to each other.

OK. Which currently installed UK methods have a neutral that is not connected to Earth by a common connection?

 

[ProDave]

OK. Which currently installed UK methods have a neutral that is not connected to Earth by a common connection?

TT for a start.Neutral is connected to an earth mat at the substation, and earth in your house is a local earth rod.

No direct connection between them, just a lot of erm earth (as in mud) between them.

 

[SPECIAL LOCATION]

SELV...??

414.4

:C

To summarise your question..

You can get a shock from a neutral conductor as it is a live conductor just as the line conductors are also live.

Neutral and the mass of earth are not at the same potential,

as can be proved with a simple continuity test between a random earth rod stuck in the ground

and a random neutral conductor somewhere on an installation.

Not forgetting that if a section of earth is made live by a supply being put directly into the gound..

You could get a shock between two physical pieces of earth as the resistance increases away from the point of supply.

Think of the numerous cases of four legged animals getting fatal shocks between two points of earth...

So during fault conditions,

as you can get a shock between two points of earth...

you can also get a shock between neutral and earth...

even if they do have an electrical connection somewhere.!!!

And Earth and Neutral are two different things...

See BS7671 definitions part 2.

 

[andrewedwardjudd]

TT for a start.

Nsutral is connected to an earth mat at the substation, and earth in your house is a local earth rod.

No direct connection between them, just a lot of erm earth (as in mud) between them.

Thanks.

Everybody.

I know it has been difficult but i do appreciate the time you have taken with me. :Applaud