Neutral Shock?

JOHNPT

Is it true that if u touch a neutral conductor say from a light u will get more of a shock then if u touched the live conductor going to the light? If this is case how come is there not the same amount of electrons flowing in both neutral and live.


Thanks

enmac

I think you are thinking of the broken neutral scenario here:

scenario 1
If the brown wire is live and you touch it you will get a belt but most of the current will still travel through and back through the neutral wiring to earth

scenario 2
If the neutral is broken and you touch the brown or the blue wire then all the current will pass through you and you will get a more severe shock.

see attached

JOHNPT

I neutral is not broken and u touch a bare live wire going to a light will u get the same level of shock as if u touched a bare neutral wire leaving a light

enmac

No, the live wire is at 230 volts - the neutral is at zero volts

mattym

If you have a broken neutral and you have a light on thats on the same circuit, you will get a shock as the live has no return path to the fuse board. It seems a worse shock to get because you dont expect to get a shock off the neutral:eek::eek::eek:

c-note

in a circuit, eg one where a light is lit and current is flowing, there are the same number of electrons flowing in the neutral as there are in the live.

however: the electrons in the live have more energy and so are at a higher voltage.
be aware that if you touch the "neutral" while its carrying a current it wont be neutral for very long:

the human bodys resistance is between 300-1000 ohms
a light bulb has a resistance of about 600 ohms
- lets say your body provides 600 ohms of resistance aswell
and you esb is at 240 volts
the light is on, and theres current flowing, and you decide to grab a bare wire
then you'll get 120v and the bulb will get 120v no matter if you touch the live or the neutral.

if the light is off and theres no circuit, ie no current flowing,
if you touch the live, you'll get 240, if you touch the neutral you get zip.

but there can occasionally be a neutral to ground voltage, but its usally fairly small (less than 10v) and wont really give you a shock.:)

enmac

c-note wrote: »

the light is on, and theres current flowing, and you decide to grab a bare wire
then you'll get 120v and the bulb will get 120v no matter if you touch the live or the neutral.
.:)

wrong here -
the neutral is at ground potential - it will not give you a shock - you will not get 120volts if you touch the neutral

enmac

mattym wrote: »

It seems a worse shock to get because you dont expect to get a shock off the neutral:eek::eek::eek:

it doesn't seem a worse shock - it actually is a worse shock because your body is carrying the full current

Solair

Neutral wires should always be treated as potentially carrying dangerous voltages. In a properly working TN-C earthing system they will be close to zero volts as they are connected to the earthing system. However, in TT systems (often found in older buildings) the neutral and local earth may not be at the same potential. It is advisable to assume that the blue or black wire could be live.

Also, it's quite possible to find a neutral colour being used as phase, particularly where DIY work was done on lighting circuits.

If in doubt, test with a phase tester and in general don't assume that any wire's safe to grab hold of unless you're 100% sure it's properly isolated.

JOHNPT

Thanks for replies but seem contradictory.

Question is If u have a light turned on and there is a live wire with some of the insulation bare on it if u touch the live wire with the light still on will u get the same level of shock as if u touched a bit of neutral wire that is bare. I do not mean to grab hold of the neutral wire so there is no return path i just mean to touch it where the insulation has been removed.

Thanks in advance

c-note

enmac wrote: »

wrong here -
the neutral is at ground potential - it will not give you a shock - you will not get 120volts if you touch the neutral

you may indeed be right,
according to multisim theres two scenarios
one, you get fried, one you dont!

scenario 1



scenario 2:

i may be wrong on this

Michael Collins

Just in case there is any confusion remaining. If the neutral is properly grounded the remote end, you will not get a shock - the voltage at the neutral end of a working bulb is essentially* zero with respect to ground.

The only exception to this is when the ground and neutral is not connected locally. This could occur, as Solair says, if the TT earthing system is the method in use.

*It is possible if there is a very high current flowing in high resistance cables, there may be sufficient voltage at the cable near the bulb to be noticable to touch - this is highly unlikely however.

In general though, as has been said, treat neutrals as live until proven otherwise.

c-note, you are talking about making youself complete the circuit by adding yourself in series with the bulb. JOHNPT is concerned with adding himself in parallel with the neutral side of the blub.

JOHNPT

So are you saying that if u touch a neutral conductor in parallel from a light u wont get a shock? Surely that is not the case and some current would flow through your body? What about if your hands were wet and u were standing on a concrete floor. Would your body resistance not be less and would not a portion of the current flow through u while the majority still goes through the neutral conductor?

Michael Collins

JOHNPT wrote: »

So are you saying that if u touch a neutral conductor in parallel from a light u wont get a shock? Surely that is not the case and some current would flow through your body? What about if your hands were wet and u were standing on a concrete floor. Would your body resistance not be less and would not a portion of the current flow through u while the majority still goes through the neutral conductor?

That is the question you asked originally yes? I've never done it, but I'd be quite confident that you won't feel anything. It's just Ohm's Law really. If you test the voltage on the neutral side with respect to Earth, you'll get effectively 0 volts. Ohm's Law says the current is V/R = 0/R = 0 amps, where R is the resistance of your body.

fishdog

I've never done it, but I'd be quite confident that you won't feel anything

I have done it. You are correct!

If you test the voltage on the neutral side with respect to Earth, you'll get effectively 0 volts. Ohm's Law says the current is V/R = 0/R = 0 amps, where R is the resistance of your body.

+1
If the neutral conductor between this point and the star point was of high impedance then things would be different because it would not be at 0 volts at this point with espect to earth. This would not be normal and would only occur if other problems existed.

This is one reason that a neutral conductor is reffered to and treated as a live conductor.

An other reason would be if the neutral conductor broke and you became "the bridge" (i.e. you made contact with both each side of the broken neutral). The load current would then pass through you. You could then get a serious shock from a neutral.

enmac

c-note wrote: »

according to multisim theres two scenarios
one, you get fried, one you dont!
i may be wrong on this

Yes c-note Indeed you are wrong, but only half wrong this time.(Possibly a communication problem between yourself and Mr.Multisim)

In your first post you stated:

"the light is on, and there's current flowing, and you decide to grab a bare wire then you'll get 120v and the bulb will get 120v no matter if you touch the live or the neutral"

Now, if the light is on and there's current flowing then it must be flowing back through the neutral and therefore the situation would be as per your bottom image where Mr.Multisim shows 0.000V.

The top image where Mr.Multisim shows 120.000V does not relate to the situation in question. This is a broken neutral situation and therefore no current would be flowing and the light would not be on.

I could be wrong..

fishdog

scenario 1
If the brown wire is live and you touch it you will get a belt but most of the current will still travel through and back through the neutral wiring to earth

The current flowing through the load will not change because the load impedance has not changed. The current flowing down the live will = the current flowing through the load + the current flowing through you
The voltage across you = The current htrough you x the impedance between you and earth

This may kill you!

scenario 2
If the neutral is broken and you touch the brown or the blue wire then all the current will pass through you and you will get a more severe shock.

If the neutral is boken and you touch the neutral you will get a smaller shock than in scenaio 1 because the impedance of your body is in series with the load impedance, therfore the overall impedance is increased, so the current is reduced. The volatge acroos you will again be = the now reduced current x the impedance of your body

enmac

fishdog wrote: »

The current flowing through the load will not change because the load impedance has not changed. The current flowing down the live will = the current flowing through the load + the current flowing through you
The voltage across you = The current htrough you x the impedance between you and earth

This may kill you!


If the neutral is boken and you touch the neutral you will get a smaller shock than in scenaio 1 because the impedance of your body is in series with the load impedance, therfore the overall impedance is increased, so the current is reduced. The volatge acroos you will again be = the now reduced current x the impedance of your body

Scenario 1 should account for the impedance between you and earth - in scenario 2 there is very little impedance as you are bridging two copper conductors.
There are quite a few variables in the argument and what you're saying is completely correct however in a domestic context and in the majority of cases I would sooner be zapped by a brown 2.5mm conductor while standing on the floor than be the bridge between two blues in a live circuit.

mattym

enmac wrote: »

it doesn't seem a worse shock - it actually is a worse shock because your body is carrying the full current

Would your body not be carrying the full current if you grabbed the live instead of the neutral???

enmac

mattym wrote: »

Would your body not be carrying the full current if you grabbed the live instead of the neutral???

mattym - see my last post

fishdog

Scenario 1 should account for the impedance between you and earth

It does. Z=V/I
The voltage is fixed (230 rms) and the current depends on the impedance. Therefore the impedance is accounted for. You essentially become a resistor in parallel with the load.

in scenario 2 there is very little impedance as you are bridging two copper conductors.

OK but you are an impedance and so is the load. This time you and the load are connected in series so the both impedances add to give a combined impedance. The sum of any two impedance added together results in a larger impedance therefore the current is reduced. The volt drop across you will be this current multiplied by your impedance.

I would sooner be zapped by a brown 2.5mm conductor while standing on the floor than be the bridge between two blues in a live circuit.

Why?? The only opposition to current flow is the impedance of your body. If you bridge the neutral then both the load impedance and you oppose current flow. Therfore the current flowing through you will be smaller. There will also be a volt drop across the load so you are getting reduced voltage also.

JOHNPT

To sum up is this correct If u touch a live conductor in series before it reaches bulb u will get more of a shock than if u touch a neutral conductor in series after the bulb.

And if u touch a live conductor in parallel before reaches the bulb u will also get more of a shock than if u touch a neutral conductor in parallel after the bulb.


So how come people say u get more of a shock or burn from a neutral conductor as its carrying the load than from a live conductor. This perception is incorrect then.

fishdog

If u touch a live conductor in series before it reaches bulb u will get more of a shock than if u touch a neutral conductor in series after the bulb.

If you complete the circuit on either side of the load the same volt drop will occur across you and the smae current will flow through you. You and the bulb are just two impedances in series so the order is irrelevent. Either way you will get the same shock

And if u touch a live conductor in parallel before reaches the bulb u will also get more of a shock than if u touch a neutral conductor in parallel after the bulb.

Correct. If you touch the live and the circuit is unbroken you will have almost 230 volts across you.
If the circuit is unbroken and you touch the neutral you will get no shock. I have done this.

So how come people say u get more of a shock or burn from a neutral conductor as its carrying the load than from a live conductor

There can be different reasons for this. I have to think about that!
Sometimes a capacitor might discharge through you through a neutral. This happened to me and it was sore!

JOHNPT

Ok thanks very much for that makes sense now. So probably only where capacitor is involved (fluorescent lights?) where u may possibly get more of a burn touching the neutral

Thanks

fishdog

So probably only where capacitor is involved (fluorescent lights?) where u may possibly get more of a burn touching the neutral

I cant remember to be honest. I want to know now myself! I will ask someone tomorrow and post it here.

Flourescent lights are far more an inductive load due to the choke, although some have capacitors in them.

Certianly neutral shocks are possible and can be nasty!

enmac

fishdog wrote: »

Why?? The only opposition to current flow is the impedance of your body

what about the return path to ground - its negligible when you're bridging two conductors as its just copper but there is a substantial impedance associated with carpets , wood flloors etc.

Its hard to quantify but on average I'm sure there would be more current flowing through you if you bridged a broken neutral than if you touched a live conductor in a domestic situation

Obviously the worst situation is where you are the bridge between a live and a neutral but you cannot liken the situation of touching a live wire to this - the overall impedance has to be accounted for - you in series with the return path

fishdog

what about the return path to ground - its negligible when you're bridging two conductors as its just copper but there is a substantial impedance associated with carpets , wood flloors etc.

Yes you are correct. There are other impedances that are in series with you and the star point of the transformer and they can vary a lot as you correctly point out.

I read your post incorrectly.

JOHNPT

however if there is a high impedance with carpets wood floors etc and u touched the neutral surely less current would flow as there would be greater impedance for electrons to earth. If u touched live the only impedance is your body. So live would give u more of a shock?

Michael Collins

JOHNPT wrote: »

however if there is a high impedance with carpets wood floors etc and u touched the neutral surely less current would flow as there would be greater impedance for electrons to earth. If u touched live the only impedance is your body. So live would give u more of a shock?

OK so here we're talking about a broken neutral. Yes, there would be less current through you if you touched the neutral but it's because the bulb (or whatever) would be in series with you, and as Fishdog says, this will add to the impedance and lower the total current flowing.

The carpets, higher floors etc has an equal effect whether you touch the live or the neutral.

JOHNPT

Actually thats not what he said. U will also be in series with the bulb if u touch the live conductor.

JOHNPT

I will post the question again giving six options of which order would give u the highest level of shock. Does the highest level of shock always result in the highest level of burns to your body.

Thanks

1 If some of the insulation was bare on live conductor to light and u touched it.
2 If some of the insulation was bare on the neutral conductor from light and u touched it.
3 If a live conductor before it reached the light was broken and u grabbed a hold of it
4 If a live conductor was broken and u grabbed hold of it with one hand and with the other hand u grabbed hold of the other end of conductor going to light ie u would be in series with the light.
5 If u grabbed hold of the broken neutral conductor coming from the light.
6 If u grabbed hold of broken neutral with one hand and with the other hand u grabbed hold of the other end of neutral conductor ie u would be in series

Thanks in advance for replies and reason why. Assume its 10 amp fuse 100 watt light bulb and u are standing on timber floors.