why neutral does not shock. how can a neutral be neutral in ac current? [duplicate]Is the neutral wire considered safe?By touching neutral why we do not get shock?Is the neutral wire considered safe?Why is there a potential difference between neutral and ground (earth)?How do I wire this AC motor to a UK plug?Why is main's neutral tied to earth?Ground losses in mains delivery networkAC transmission just requires live wire, why is neutral presentCan I put a low current relay between line (or neutral) and the ground wires to detect polarity?Live wire and ground questionWhy do we not get shocked by neutral wire and how can it behave as it does?
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why neutral does not shock. how can a neutral be neutral in ac current? [duplicate]
Is the neutral wire considered safe?By touching neutral why we do not get shock?Is the neutral wire considered safe?Why is there a potential difference between neutral and ground (earth)?How do I wire this AC motor to a UK plug?Why is main's neutral tied to earth?Ground losses in mains delivery networkAC transmission just requires live wire, why is neutral presentCan I put a low current relay between line (or neutral) and the ground wires to detect polarity?Live wire and ground questionWhy do we not get shocked by neutral wire and how can it behave as it does?
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This question already has an answer here:
Is the neutral wire considered safe?
4 answers
When I probe my city mains with one probe in the live and one in earth (which should be 0 volt) it shows a voltage of around 250v. But when I probe the neutral and the earth it shows no voltage. I know that current runs in one direction for 50 times in a second. So the neutral should act like live for 50 times in a second. Then neutral should show some voltage with the earth, which it doesn't. If you touch the neutral wire you won't get shocked but if you touch the live the wire you get shocked why and how?
ac power-electronics mains
edited Jul 21 at 12:21
jusaca
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asked Jul 21 at 4:56
JyotirJyotir
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marked as duplicate by Huisman, JRE, Leon Heller, Dmitry Grigoryev, Nick Alexeev♦ Jul 22 at 14:07
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
|
show 2 more comments
$begingroup$
This question already has an answer here:
Is the neutral wire considered safe?
4 answers
When I probe my city mains with one probe in the live and one in earth (which should be 0 volt) it shows a voltage of around 250v. But when I probe the neutral and the earth it shows no voltage. I know that current runs in one direction for 50 times in a second. So the neutral should act like live for 50 times in a second. Then neutral should show some voltage with the earth, which it doesn't. If you touch the neutral wire you won't get shocked but if you touch the live the wire you get shocked why and how?
ac power-electronics mains
edited Jul 21 at 12:21
jusaca
2,9682 gold badges11 silver badges35 bronze badges
asked Jul 21 at 4:56
JyotirJyotir
551 silver badge7 bronze badges
$endgroup$
marked as duplicate by Huisman, JRE, Leon Heller, Dmitry Grigoryev, Nick Alexeev♦ Jul 22 at 14:07
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
1
$begingroup$
i can get shocked by live even if there is no load due to parasitic capacitance , but why does nuetral not behave the same
$endgroup$
– Jyotir
Jul 21 at 5:00
$begingroup$
so that means if touch the nuetral(which i am not going to) it will still shock me.my main question here is why is nuetral 0 volt or ground
$endgroup$
– Jyotir
Jul 21 at 5:02
5
$begingroup$
You have a misunderstanding about voltage measurements.
$endgroup$
– DKNguyen
Jul 21 at 5:03
2
$begingroup$
please help me clear the misunderstanding
$endgroup$
– Jyotir
Jul 21 at 5:05
$begingroup$
In case someone thinks tldr; YOU CAN GET SHOCKED BY TOUCHING NEUTRAL
$endgroup$
– Huisman
Jul 21 at 6:06
|
show 2 more comments
$begingroup$
This question already has an answer here:
Is the neutral wire considered safe?
4 answers
When I probe my city mains with one probe in the live and one in earth (which should be 0 volt) it shows a voltage of around 250v. But when I probe the neutral and the earth it shows no voltage. I know that current runs in one direction for 50 times in a second. So the neutral should act like live for 50 times in a second. Then neutral should show some voltage with the earth, which it doesn't. If you touch the neutral wire you won't get shocked but if you touch the live the wire you get shocked why and how?
ac power-electronics mains
edited Jul 21 at 12:21
jusaca
2,9682 gold badges11 silver badges35 bronze badges
asked Jul 21 at 4:56
JyotirJyotir
551 silver badge7 bronze badges
$endgroup$
This question already has an answer here:
Is the neutral wire considered safe?
4 answers
When I probe my city mains with one probe in the live and one in earth (which should be 0 volt) it shows a voltage of around 250v. But when I probe the neutral and the earth it shows no voltage. I know that current runs in one direction for 50 times in a second. So the neutral should act like live for 50 times in a second. Then neutral should show some voltage with the earth, which it doesn't. If you touch the neutral wire you won't get shocked but if you touch the live the wire you get shocked why and how?
This question already has an answer here:
Is the neutral wire considered safe?
4 answers
ac power-electronics mains
ac power-electronics mains
edited Jul 21 at 12:21
jusaca
2,9682 gold badges11 silver badges35 bronze badges
asked Jul 21 at 4:56
JyotirJyotir
551 silver badge7 bronze badges
edited Jul 21 at 12:21
jusaca
2,9682 gold badges11 silver badges35 bronze badges
asked Jul 21 at 4:56
JyotirJyotir
551 silver badge7 bronze badges
edited Jul 21 at 12:21
jusaca
2,9682 gold badges11 silver badges35 bronze badges
edited Jul 21 at 12:21
jusaca
2,9682 gold badges11 silver badges35 bronze badges
edited Jul 21 at 12:21
jusaca
2,9682 gold badges11 silver badges35 bronze badges
2,9682 gold badges11 silver badges35 bronze badges
asked Jul 21 at 4:56
JyotirJyotir
551 silver badge7 bronze badges
asked Jul 21 at 4:56
JyotirJyotir
551 silver badge7 bronze badges
asked Jul 21 at 4:56
JyotirJyotir
551 silver badge7 bronze badges
551 silver badge7 bronze badges
marked as duplicate by Huisman, JRE, Leon Heller, Dmitry Grigoryev, Nick Alexeev♦ Jul 22 at 14:07
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
marked as duplicate by Huisman, JRE, Leon Heller, Dmitry Grigoryev, Nick Alexeev♦ Jul 22 at 14:07
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
marked as duplicate by Huisman, JRE, Leon Heller, Dmitry Grigoryev, Nick Alexeev♦ Jul 22 at 14:07
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
1
$begingroup$
i can get shocked by live even if there is no load due to parasitic capacitance , but why does nuetral not behave the same
$endgroup$
– Jyotir
Jul 21 at 5:00
$begingroup$
so that means if touch the nuetral(which i am not going to) it will still shock me.my main question here is why is nuetral 0 volt or ground
$endgroup$
– Jyotir
Jul 21 at 5:02
5
$begingroup$
You have a misunderstanding about voltage measurements.
$endgroup$
– DKNguyen
Jul 21 at 5:03
2
$begingroup$
please help me clear the misunderstanding
$endgroup$
– Jyotir
Jul 21 at 5:05
$begingroup$
In case someone thinks tldr; YOU CAN GET SHOCKED BY TOUCHING NEUTRAL
$endgroup$
– Huisman
Jul 21 at 6:06
|
show 2 more comments
1
$begingroup$
i can get shocked by live even if there is no load due to parasitic capacitance , but why does nuetral not behave the same
$endgroup$
– Jyotir
Jul 21 at 5:00
$begingroup$
so that means if touch the nuetral(which i am not going to) it will still shock me.my main question here is why is nuetral 0 volt or ground
$endgroup$
– Jyotir
Jul 21 at 5:02
5
$begingroup$
You have a misunderstanding about voltage measurements.
$endgroup$
– DKNguyen
Jul 21 at 5:03
2
$begingroup$
please help me clear the misunderstanding
$endgroup$
– Jyotir
Jul 21 at 5:05
$begingroup$
In case someone thinks tldr; YOU CAN GET SHOCKED BY TOUCHING NEUTRAL
$endgroup$
– Huisman
Jul 21 at 6:06
1
1
$begingroup$
i can get shocked by live even if there is no load due to parasitic capacitance , but why does nuetral not behave the same
$endgroup$
– Jyotir
Jul 21 at 5:00
$begingroup$
i can get shocked by live even if there is no load due to parasitic capacitance , but why does nuetral not behave the same
$endgroup$
– Jyotir
Jul 21 at 5:00
$begingroup$
so that means if touch the nuetral(which i am not going to) it will still shock me.my main question here is why is nuetral 0 volt or ground
$endgroup$
– Jyotir
Jul 21 at 5:02
$begingroup$
so that means if touch the nuetral(which i am not going to) it will still shock me.my main question here is why is nuetral 0 volt or ground
$endgroup$
– Jyotir
Jul 21 at 5:02
5
5
$begingroup$
You have a misunderstanding about voltage measurements.
$endgroup$
– DKNguyen
Jul 21 at 5:03
$begingroup$
You have a misunderstanding about voltage measurements.
$endgroup$
– DKNguyen
Jul 21 at 5:03
2
2
$begingroup$
please help me clear the misunderstanding
$endgroup$
– Jyotir
Jul 21 at 5:05
$begingroup$
please help me clear the misunderstanding
$endgroup$
– Jyotir
Jul 21 at 5:05
$begingroup$
In case someone thinks tldr; YOU CAN GET SHOCKED BY TOUCHING NEUTRAL
$endgroup$
– Huisman
Jul 21 at 6:06
$begingroup$
In case someone thinks tldr; YOU CAN GET SHOCKED BY TOUCHING NEUTRAL
$endgroup$
– Huisman
Jul 21 at 6:06
|
show 2 more comments
5 Answers
5
active
oldest
votes
$begingroup$
We force it to be that way
Mains power is wired as an isolated system, with an asterisk. The asterisk came about for some very good reasons. The "safeness" of neutral is a side-effect, and an optional one.
If mains power were an isolated system (And I've run it that way, and it works), and you are grounded presumably... then it wouldn't matter if you touched pole 1 or center (I won't call it "neutral"). No current would flow. The hot and center have no relationship with earth (except through you, and with only one "wire", it's an open circuit). The system "floats".
An isolated system is exactly what you expect.
However, we build mains power to be resilient when something goes wrong. Things can go wrong with isolated systems, and one of the scariest is a transformer leak. If transformer primary leaks (even a little) into the secondary, or if there is capacitive coupling, then it de-isolates the isolated system, and "pulls it up" to thousands of volts compared to ground. Now we have a problem. In that lathe motor, coffee maker or LED light, the insulation is not rated for thousands of volts.
The equipotential bond makes the neutral
To prevent the secondary ("isolated system") from floating at high voltages, we intentionally add an equipotential bond to force a relationship to earth. You might use a transformer for the equipotential bond, e.g. in 3-phase delta (non-wild-leg) to put earth in the middle. You could also use a car battery, giving the system a 12VDC bias from earth. But usually, you use the cheapest equipotential bond available: a piece of wire. You bond one of the conductors to ground, typically "center". **Because it is bonded to earth, you label it 'Neutral'.
It really doesn't matter which supply wire you bond to neutral. Ideally you want to minimize the voltage (to earth) of the hottest hot, so the best choice is in the electrical "center" ... however, 240V wild-leg delta is an example of not doing that.
So to answer your question, neutral is cold because we made it cold.
Neutral is not quiescent; it pulses at line frequency just like the hot. The effect of the equipotential bond is to dynamically change the bias of the whole transformer secondary, to keep neutral at earth potential and make hot move away from it.
Other useful reasons
A desired side-effect of the equipotential bond is that if there is a hot-earth fault, there is a high-current path via ground wire, conduit etc. back to the neutral-earth equipotential bond, and ultimately back to neutral. This completes the circuit, allows high current to flow, and causes a circuit breaker trip, which arrests the ground fault. Remember, current wants to return to source, not to ground. It doesn't care about ground, except that the equipotential bond makes it care.
For a variety of reasons, there needs to be exactly one equipotential bond. Another one would create redundant (paralleled) paths for normal neutral (return) current, and that causes all sorts of mischief.
answered Jul 21 at 15:15
HarperHarper
8,42711 silver badges33 bronze badges
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+1 ad infinitum for "Remember, current wants to return to source, not to ground. It doesn't care about ground, except that the equipotential bond makes it care."
$endgroup$
– Shamtam
Jul 22 at 12:35
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When I probe my city mains with one probe in the live and one in earth (which should be 0 volt) it shows a voltage of around 250 V.
That's correct - if a little high.
But when I probe the neutral and the earth it shows no voltage.
That's good too. That line has been "neutralised" by a connection to earth at your supply transformer and, depending on your local regulations, at the supply entrance to your building.
I know that current runs in one direction for 50 times in a second. So the neutral should act like live for 50 times in a second of a second[?]. Then neutral should show some voltage with the earth, which it doesn't.
No, this thinking is not correct.
simulate this circuit – Schematic created using CircuitLab
Figure 1. Voltage measurements during positive and negative mains peaks.
The mains voltage peaks at $ sqrt 2 $ times the RMS voltage. For your 250 V RMS supply that will be about 350 V peak. If you had a fast-acting DC meter with max / min peak hold function you would be able to take the readings indicated in Figure 1. Neutral stays at 0 V and the live wire polarity alternates.
If you touch the neutral wire you won't get shocked but if you touch the live the wire you get shocked why and how?
Because the neutral has been neutralised. There is no voltage on it with respect to ground.
A note of caution
Since all wires have resistance there is a low voltage on the mains neutral and this increases with the current. If, for example, the neutral from your socket has a resistance of 0.2 Ω back to the fuseboard then a current of 10 A will cause the neutral voltage to rise to $ V = IR = 10 times 0.2 = 2 text V $.
simulate this circuit
Figure 2. The disconnected neutral wire turns live.
Also be aware that if the neutral conductor breaks and anything is plugged in to the circuit then the neutral wire may go live. Never assume that a mains conductor is at 0 V. Isolate properly.
answered Jul 21 at 8:12
TransistorTransistor
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Is figure 2 an example of an incorrectly wired circuit? You aren't normally suppose to wire connections in a series like that right? Precisely due to the risk of the neutral going live.
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– Nelson
Jul 22 at 1:35
$begingroup$
@Nelson I'd say it's an example of a faulty circuit - i.e one where the neutral wire was broken, or indeed installed incorrectly. It wont work (light wouldn't turn on), untill the neutral is properly connected. What do you mean by "in series" here? This (with the neutral connected) is how it normally is - the lamp and the switch have to be in series, how else would it work?
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– JonasCz - Reinstate Monica
Jul 22 at 5:18
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Oh, ok, that makes sense. The open circuit caused by a broken wire, not someone deliberately putting a junction box there. That makes sense. A broken neutral will definitely shock if someone is stupid enough to grab the two broken wires of the neutral and complete the circuit.
$endgroup$
– Nelson
Jul 22 at 5:25
$begingroup$
@Nelson: I've added some text to Figure 2 to clarify. Since the transformer secondary is earthed one could get a shock by touching 'NEUTRAL' and earth. The body's capacitance to earth may be enough to shock even without a direct connection.
$endgroup$
– Transistor
Jul 22 at 6:11
2
$begingroup$
@Nelson It's not so much "someone is stupid enough to grab the two broken wires", but an example of what could happen to someone poking around the lamp socket, believing themselves "safe" in the knowledge that "the neutral is at zero volts" ... a break in the neutral anywhere from the lamp back to the distribution panel could expose them to the full mains potential.
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– TripeHound
Jul 22 at 10:54
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The neutral does not act like the live because the neutral is tied to ground at a single point somwhere.
You are imagining the neutral and live both move above and below each other about ground. Relative to each other, the neutral and live do move above and below each other. This is if you think of them in complete isolation relative to each other and only each other.
In the real world there are more absolute voltage potentials like ground or earth. If left to float, the live and neutral move together above and below some common-mode voltage. But in the real world we tie the neutral to ground for safety purposes. We don't want the live and neutral floating to whatever common mode voltage they feel like. The equipment probably wouldn't care and would still function since it only cares about what live and neutral are relative to each other, but it's dangerous to you (who is at ground potential) if their common mode voltage floats up to 1kV relative to ground.
Since the neutral is tied to ground somewhere, then the neutral becomes more or less fixed to ground. In that case, live line ends up doing all the movement above and below the neutral.
That said, you can still get shocked by the neutral if there is a load. The neutral is tied to ground SOMEWHERE but that somewhere might be quite far from where you are looking at the neutral. That means there is an impedance between where the neutral connects to ground and where you are looking at the neutral.
So if there is no load current then nothing disturbs that impedance and the neutral sits at ground. But if there is a load current, then the voltage developed across that impedance can be enough to have the neutral voltage rise above ground to shockable levels when there is a load current.
answered Jul 21 at 5:02
DKNguyenDKNguyen
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As regards electricity, what matters is the potential difference (this is the reason why you need to touch two points to get shocked).
Usually, the neutral and ground are at the same potential and a simultaneous contact is harmless. On the opposite, touching the live and one of ground or neutral is to be avoided.
There can be faulty situations where there is a potential difference between ground and neutral (floating ground), even though the tension between neutral and live is normal.
answered Jul 21 at 15:42
Yves DaoustYves Daoust
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Neutral stays close to the same potential as 'earth' because they are shorted at your local power source.
The AC of live is plus or minus compared to neutral.
Regarding shock, consider that one end of 'you' is at same potential as earth (e.g. your bare feet on the ground). Then only if the other end is at a big enough potential difference away, THEN you experience a shock.
answered Jul 21 at 16:33
KripacharyaKripacharya
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5 Answers
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5 Answers
5
active
oldest
votes
active
oldest
votes
active
oldest
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$begingroup$
We force it to be that way
Mains power is wired as an isolated system, with an asterisk. The asterisk came about for some very good reasons. The "safeness" of neutral is a side-effect, and an optional one.
If mains power were an isolated system (And I've run it that way, and it works), and you are grounded presumably... then it wouldn't matter if you touched pole 1 or center (I won't call it "neutral"). No current would flow. The hot and center have no relationship with earth (except through you, and with only one "wire", it's an open circuit). The system "floats".
An isolated system is exactly what you expect.
However, we build mains power to be resilient when something goes wrong. Things can go wrong with isolated systems, and one of the scariest is a transformer leak. If transformer primary leaks (even a little) into the secondary, or if there is capacitive coupling, then it de-isolates the isolated system, and "pulls it up" to thousands of volts compared to ground. Now we have a problem. In that lathe motor, coffee maker or LED light, the insulation is not rated for thousands of volts.
The equipotential bond makes the neutral
To prevent the secondary ("isolated system") from floating at high voltages, we intentionally add an equipotential bond to force a relationship to earth. You might use a transformer for the equipotential bond, e.g. in 3-phase delta (non-wild-leg) to put earth in the middle. You could also use a car battery, giving the system a 12VDC bias from earth. But usually, you use the cheapest equipotential bond available: a piece of wire. You bond one of the conductors to ground, typically "center". **Because it is bonded to earth, you label it 'Neutral'.
It really doesn't matter which supply wire you bond to neutral. Ideally you want to minimize the voltage (to earth) of the hottest hot, so the best choice is in the electrical "center" ... however, 240V wild-leg delta is an example of not doing that.
So to answer your question, neutral is cold because we made it cold.
Neutral is not quiescent; it pulses at line frequency just like the hot. The effect of the equipotential bond is to dynamically change the bias of the whole transformer secondary, to keep neutral at earth potential and make hot move away from it.
Other useful reasons
A desired side-effect of the equipotential bond is that if there is a hot-earth fault, there is a high-current path via ground wire, conduit etc. back to the neutral-earth equipotential bond, and ultimately back to neutral. This completes the circuit, allows high current to flow, and causes a circuit breaker trip, which arrests the ground fault. Remember, current wants to return to source, not to ground. It doesn't care about ground, except that the equipotential bond makes it care.
For a variety of reasons, there needs to be exactly one equipotential bond. Another one would create redundant (paralleled) paths for normal neutral (return) current, and that causes all sorts of mischief.
answered Jul 21 at 15:15
HarperHarper
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+1 ad infinitum for "Remember, current wants to return to source, not to ground. It doesn't care about ground, except that the equipotential bond makes it care."
$endgroup$
– Shamtam
Jul 22 at 12:35
add a comment
|
$begingroup$
We force it to be that way
Mains power is wired as an isolated system, with an asterisk. The asterisk came about for some very good reasons. The "safeness" of neutral is a side-effect, and an optional one.
If mains power were an isolated system (And I've run it that way, and it works), and you are grounded presumably... then it wouldn't matter if you touched pole 1 or center (I won't call it "neutral"). No current would flow. The hot and center have no relationship with earth (except through you, and with only one "wire", it's an open circuit). The system "floats".
An isolated system is exactly what you expect.
However, we build mains power to be resilient when something goes wrong. Things can go wrong with isolated systems, and one of the scariest is a transformer leak. If transformer primary leaks (even a little) into the secondary, or if there is capacitive coupling, then it de-isolates the isolated system, and "pulls it up" to thousands of volts compared to ground. Now we have a problem. In that lathe motor, coffee maker or LED light, the insulation is not rated for thousands of volts.
The equipotential bond makes the neutral
To prevent the secondary ("isolated system") from floating at high voltages, we intentionally add an equipotential bond to force a relationship to earth. You might use a transformer for the equipotential bond, e.g. in 3-phase delta (non-wild-leg) to put earth in the middle. You could also use a car battery, giving the system a 12VDC bias from earth. But usually, you use the cheapest equipotential bond available: a piece of wire. You bond one of the conductors to ground, typically "center". **Because it is bonded to earth, you label it 'Neutral'.
It really doesn't matter which supply wire you bond to neutral. Ideally you want to minimize the voltage (to earth) of the hottest hot, so the best choice is in the electrical "center" ... however, 240V wild-leg delta is an example of not doing that.
So to answer your question, neutral is cold because we made it cold.
Neutral is not quiescent; it pulses at line frequency just like the hot. The effect of the equipotential bond is to dynamically change the bias of the whole transformer secondary, to keep neutral at earth potential and make hot move away from it.
Other useful reasons
A desired side-effect of the equipotential bond is that if there is a hot-earth fault, there is a high-current path via ground wire, conduit etc. back to the neutral-earth equipotential bond, and ultimately back to neutral. This completes the circuit, allows high current to flow, and causes a circuit breaker trip, which arrests the ground fault. Remember, current wants to return to source, not to ground. It doesn't care about ground, except that the equipotential bond makes it care.
For a variety of reasons, there needs to be exactly one equipotential bond. Another one would create redundant (paralleled) paths for normal neutral (return) current, and that causes all sorts of mischief.
answered Jul 21 at 15:15
HarperHarper
8,42711 silver badges33 bronze badges
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+1 ad infinitum for "Remember, current wants to return to source, not to ground. It doesn't care about ground, except that the equipotential bond makes it care."
$endgroup$
– Shamtam
Jul 22 at 12:35
add a comment
|
$begingroup$
We force it to be that way
Mains power is wired as an isolated system, with an asterisk. The asterisk came about for some very good reasons. The "safeness" of neutral is a side-effect, and an optional one.
If mains power were an isolated system (And I've run it that way, and it works), and you are grounded presumably... then it wouldn't matter if you touched pole 1 or center (I won't call it "neutral"). No current would flow. The hot and center have no relationship with earth (except through you, and with only one "wire", it's an open circuit). The system "floats".
An isolated system is exactly what you expect.
However, we build mains power to be resilient when something goes wrong. Things can go wrong with isolated systems, and one of the scariest is a transformer leak. If transformer primary leaks (even a little) into the secondary, or if there is capacitive coupling, then it de-isolates the isolated system, and "pulls it up" to thousands of volts compared to ground. Now we have a problem. In that lathe motor, coffee maker or LED light, the insulation is not rated for thousands of volts.
The equipotential bond makes the neutral
To prevent the secondary ("isolated system") from floating at high voltages, we intentionally add an equipotential bond to force a relationship to earth. You might use a transformer for the equipotential bond, e.g. in 3-phase delta (non-wild-leg) to put earth in the middle. You could also use a car battery, giving the system a 12VDC bias from earth. But usually, you use the cheapest equipotential bond available: a piece of wire. You bond one of the conductors to ground, typically "center". **Because it is bonded to earth, you label it 'Neutral'.
It really doesn't matter which supply wire you bond to neutral. Ideally you want to minimize the voltage (to earth) of the hottest hot, so the best choice is in the electrical "center" ... however, 240V wild-leg delta is an example of not doing that.
So to answer your question, neutral is cold because we made it cold.
Neutral is not quiescent; it pulses at line frequency just like the hot. The effect of the equipotential bond is to dynamically change the bias of the whole transformer secondary, to keep neutral at earth potential and make hot move away from it.
Other useful reasons
A desired side-effect of the equipotential bond is that if there is a hot-earth fault, there is a high-current path via ground wire, conduit etc. back to the neutral-earth equipotential bond, and ultimately back to neutral. This completes the circuit, allows high current to flow, and causes a circuit breaker trip, which arrests the ground fault. Remember, current wants to return to source, not to ground. It doesn't care about ground, except that the equipotential bond makes it care.
For a variety of reasons, there needs to be exactly one equipotential bond. Another one would create redundant (paralleled) paths for normal neutral (return) current, and that causes all sorts of mischief.
answered Jul 21 at 15:15
HarperHarper
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We force it to be that way
Mains power is wired as an isolated system, with an asterisk. The asterisk came about for some very good reasons. The "safeness" of neutral is a side-effect, and an optional one.
If mains power were an isolated system (And I've run it that way, and it works), and you are grounded presumably... then it wouldn't matter if you touched pole 1 or center (I won't call it "neutral"). No current would flow. The hot and center have no relationship with earth (except through you, and with only one "wire", it's an open circuit). The system "floats".
An isolated system is exactly what you expect.
However, we build mains power to be resilient when something goes wrong. Things can go wrong with isolated systems, and one of the scariest is a transformer leak. If transformer primary leaks (even a little) into the secondary, or if there is capacitive coupling, then it de-isolates the isolated system, and "pulls it up" to thousands of volts compared to ground. Now we have a problem. In that lathe motor, coffee maker or LED light, the insulation is not rated for thousands of volts.
The equipotential bond makes the neutral
To prevent the secondary ("isolated system") from floating at high voltages, we intentionally add an equipotential bond to force a relationship to earth. You might use a transformer for the equipotential bond, e.g. in 3-phase delta (non-wild-leg) to put earth in the middle. You could also use a car battery, giving the system a 12VDC bias from earth. But usually, you use the cheapest equipotential bond available: a piece of wire. You bond one of the conductors to ground, typically "center". **Because it is bonded to earth, you label it 'Neutral'.
It really doesn't matter which supply wire you bond to neutral. Ideally you want to minimize the voltage (to earth) of the hottest hot, so the best choice is in the electrical "center" ... however, 240V wild-leg delta is an example of not doing that.
So to answer your question, neutral is cold because we made it cold.
Neutral is not quiescent; it pulses at line frequency just like the hot. The effect of the equipotential bond is to dynamically change the bias of the whole transformer secondary, to keep neutral at earth potential and make hot move away from it.
Other useful reasons
A desired side-effect of the equipotential bond is that if there is a hot-earth fault, there is a high-current path via ground wire, conduit etc. back to the neutral-earth equipotential bond, and ultimately back to neutral. This completes the circuit, allows high current to flow, and causes a circuit breaker trip, which arrests the ground fault. Remember, current wants to return to source, not to ground. It doesn't care about ground, except that the equipotential bond makes it care.
For a variety of reasons, there needs to be exactly one equipotential bond. Another one would create redundant (paralleled) paths for normal neutral (return) current, and that causes all sorts of mischief.
answered Jul 21 at 15:15
HarperHarper
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edited Jul 21 at 16:43
answered Jul 21 at 15:15
HarperHarper
8,42711 silver badges33 bronze badges
answered Jul 21 at 15:15
HarperHarper
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answered Jul 21 at 15:15
HarperHarper
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8,42711 silver badges33 bronze badges
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+1 ad infinitum for "Remember, current wants to return to source, not to ground. It doesn't care about ground, except that the equipotential bond makes it care."
$endgroup$
– Shamtam
Jul 22 at 12:35
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+1 ad infinitum for "Remember, current wants to return to source, not to ground. It doesn't care about ground, except that the equipotential bond makes it care."
$endgroup$
– Shamtam
Jul 22 at 12:35
$begingroup$
+1 ad infinitum for "Remember, current wants to return to source, not to ground. It doesn't care about ground, except that the equipotential bond makes it care."
$endgroup$
– Shamtam
Jul 22 at 12:35
$begingroup$
+1 ad infinitum for "Remember, current wants to return to source, not to ground. It doesn't care about ground, except that the equipotential bond makes it care."
$endgroup$
– Shamtam
Jul 22 at 12:35
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When I probe my city mains with one probe in the live and one in earth (which should be 0 volt) it shows a voltage of around 250 V.
That's correct - if a little high.
But when I probe the neutral and the earth it shows no voltage.
That's good too. That line has been "neutralised" by a connection to earth at your supply transformer and, depending on your local regulations, at the supply entrance to your building.
I know that current runs in one direction for 50 times in a second. So the neutral should act like live for 50 times in a second of a second[?]. Then neutral should show some voltage with the earth, which it doesn't.
No, this thinking is not correct.
simulate this circuit – Schematic created using CircuitLab
Figure 1. Voltage measurements during positive and negative mains peaks.
The mains voltage peaks at $ sqrt 2 $ times the RMS voltage. For your 250 V RMS supply that will be about 350 V peak. If you had a fast-acting DC meter with max / min peak hold function you would be able to take the readings indicated in Figure 1. Neutral stays at 0 V and the live wire polarity alternates.
If you touch the neutral wire you won't get shocked but if you touch the live the wire you get shocked why and how?
Because the neutral has been neutralised. There is no voltage on it with respect to ground.
A note of caution
Since all wires have resistance there is a low voltage on the mains neutral and this increases with the current. If, for example, the neutral from your socket has a resistance of 0.2 Ω back to the fuseboard then a current of 10 A will cause the neutral voltage to rise to $ V = IR = 10 times 0.2 = 2 text V $.
simulate this circuit
Figure 2. The disconnected neutral wire turns live.
Also be aware that if the neutral conductor breaks and anything is plugged in to the circuit then the neutral wire may go live. Never assume that a mains conductor is at 0 V. Isolate properly.
answered Jul 21 at 8:12
TransistorTransistor
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Is figure 2 an example of an incorrectly wired circuit? You aren't normally suppose to wire connections in a series like that right? Precisely due to the risk of the neutral going live.
$endgroup$
– Nelson
Jul 22 at 1:35
$begingroup$
@Nelson I'd say it's an example of a faulty circuit - i.e one where the neutral wire was broken, or indeed installed incorrectly. It wont work (light wouldn't turn on), untill the neutral is properly connected. What do you mean by "in series" here? This (with the neutral connected) is how it normally is - the lamp and the switch have to be in series, how else would it work?
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– JonasCz - Reinstate Monica
Jul 22 at 5:18
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Oh, ok, that makes sense. The open circuit caused by a broken wire, not someone deliberately putting a junction box there. That makes sense. A broken neutral will definitely shock if someone is stupid enough to grab the two broken wires of the neutral and complete the circuit.
$endgroup$
– Nelson
Jul 22 at 5:25
$begingroup$
@Nelson: I've added some text to Figure 2 to clarify. Since the transformer secondary is earthed one could get a shock by touching 'NEUTRAL' and earth. The body's capacitance to earth may be enough to shock even without a direct connection.
$endgroup$
– Transistor
Jul 22 at 6:11
2
$begingroup$
@Nelson It's not so much "someone is stupid enough to grab the two broken wires", but an example of what could happen to someone poking around the lamp socket, believing themselves "safe" in the knowledge that "the neutral is at zero volts" ... a break in the neutral anywhere from the lamp back to the distribution panel could expose them to the full mains potential.
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– TripeHound
Jul 22 at 10:54
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When I probe my city mains with one probe in the live and one in earth (which should be 0 volt) it shows a voltage of around 250 V.
That's correct - if a little high.
But when I probe the neutral and the earth it shows no voltage.
That's good too. That line has been "neutralised" by a connection to earth at your supply transformer and, depending on your local regulations, at the supply entrance to your building.
I know that current runs in one direction for 50 times in a second. So the neutral should act like live for 50 times in a second of a second[?]. Then neutral should show some voltage with the earth, which it doesn't.
No, this thinking is not correct.
simulate this circuit – Schematic created using CircuitLab
Figure 1. Voltage measurements during positive and negative mains peaks.
The mains voltage peaks at $ sqrt 2 $ times the RMS voltage. For your 250 V RMS supply that will be about 350 V peak. If you had a fast-acting DC meter with max / min peak hold function you would be able to take the readings indicated in Figure 1. Neutral stays at 0 V and the live wire polarity alternates.
If you touch the neutral wire you won't get shocked but if you touch the live the wire you get shocked why and how?
Because the neutral has been neutralised. There is no voltage on it with respect to ground.
A note of caution
Since all wires have resistance there is a low voltage on the mains neutral and this increases with the current. If, for example, the neutral from your socket has a resistance of 0.2 Ω back to the fuseboard then a current of 10 A will cause the neutral voltage to rise to $ V = IR = 10 times 0.2 = 2 text V $.
simulate this circuit
Figure 2. The disconnected neutral wire turns live.
Also be aware that if the neutral conductor breaks and anything is plugged in to the circuit then the neutral wire may go live. Never assume that a mains conductor is at 0 V. Isolate properly.
answered Jul 21 at 8:12
TransistorTransistor
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$endgroup$
$begingroup$
Is figure 2 an example of an incorrectly wired circuit? You aren't normally suppose to wire connections in a series like that right? Precisely due to the risk of the neutral going live.
$endgroup$
– Nelson
Jul 22 at 1:35
$begingroup$
@Nelson I'd say it's an example of a faulty circuit - i.e one where the neutral wire was broken, or indeed installed incorrectly. It wont work (light wouldn't turn on), untill the neutral is properly connected. What do you mean by "in series" here? This (with the neutral connected) is how it normally is - the lamp and the switch have to be in series, how else would it work?
$endgroup$
– JonasCz - Reinstate Monica
Jul 22 at 5:18
$begingroup$
Oh, ok, that makes sense. The open circuit caused by a broken wire, not someone deliberately putting a junction box there. That makes sense. A broken neutral will definitely shock if someone is stupid enough to grab the two broken wires of the neutral and complete the circuit.
$endgroup$
– Nelson
Jul 22 at 5:25
$begingroup$
@Nelson: I've added some text to Figure 2 to clarify. Since the transformer secondary is earthed one could get a shock by touching 'NEUTRAL' and earth. The body's capacitance to earth may be enough to shock even without a direct connection.
$endgroup$
– Transistor
Jul 22 at 6:11
2
$begingroup$
@Nelson It's not so much "someone is stupid enough to grab the two broken wires", but an example of what could happen to someone poking around the lamp socket, believing themselves "safe" in the knowledge that "the neutral is at zero volts" ... a break in the neutral anywhere from the lamp back to the distribution panel could expose them to the full mains potential.
$endgroup$
– TripeHound
Jul 22 at 10:54
add a comment
|
$begingroup$
When I probe my city mains with one probe in the live and one in earth (which should be 0 volt) it shows a voltage of around 250 V.
That's correct - if a little high.
But when I probe the neutral and the earth it shows no voltage.
That's good too. That line has been "neutralised" by a connection to earth at your supply transformer and, depending on your local regulations, at the supply entrance to your building.
I know that current runs in one direction for 50 times in a second. So the neutral should act like live for 50 times in a second of a second[?]. Then neutral should show some voltage with the earth, which it doesn't.
No, this thinking is not correct.
simulate this circuit – Schematic created using CircuitLab
Figure 1. Voltage measurements during positive and negative mains peaks.
The mains voltage peaks at $ sqrt 2 $ times the RMS voltage. For your 250 V RMS supply that will be about 350 V peak. If you had a fast-acting DC meter with max / min peak hold function you would be able to take the readings indicated in Figure 1. Neutral stays at 0 V and the live wire polarity alternates.
If you touch the neutral wire you won't get shocked but if you touch the live the wire you get shocked why and how?
Because the neutral has been neutralised. There is no voltage on it with respect to ground.
A note of caution
Since all wires have resistance there is a low voltage on the mains neutral and this increases with the current. If, for example, the neutral from your socket has a resistance of 0.2 Ω back to the fuseboard then a current of 10 A will cause the neutral voltage to rise to $ V = IR = 10 times 0.2 = 2 text V $.
simulate this circuit
Figure 2. The disconnected neutral wire turns live.
Also be aware that if the neutral conductor breaks and anything is plugged in to the circuit then the neutral wire may go live. Never assume that a mains conductor is at 0 V. Isolate properly.
answered Jul 21 at 8:12
TransistorTransistor
102k9 gold badges104 silver badges227 bronze badges
$endgroup$
When I probe my city mains with one probe in the live and one in earth (which should be 0 volt) it shows a voltage of around 250 V.
That's correct - if a little high.
But when I probe the neutral and the earth it shows no voltage.
That's good too. That line has been "neutralised" by a connection to earth at your supply transformer and, depending on your local regulations, at the supply entrance to your building.
I know that current runs in one direction for 50 times in a second. So the neutral should act like live for 50 times in a second of a second[?]. Then neutral should show some voltage with the earth, which it doesn't.
No, this thinking is not correct.
simulate this circuit – Schematic created using CircuitLab
Figure 1. Voltage measurements during positive and negative mains peaks.
The mains voltage peaks at $ sqrt 2 $ times the RMS voltage. For your 250 V RMS supply that will be about 350 V peak. If you had a fast-acting DC meter with max / min peak hold function you would be able to take the readings indicated in Figure 1. Neutral stays at 0 V and the live wire polarity alternates.
If you touch the neutral wire you won't get shocked but if you touch the live the wire you get shocked why and how?
Because the neutral has been neutralised. There is no voltage on it with respect to ground.
A note of caution
Since all wires have resistance there is a low voltage on the mains neutral and this increases with the current. If, for example, the neutral from your socket has a resistance of 0.2 Ω back to the fuseboard then a current of 10 A will cause the neutral voltage to rise to $ V = IR = 10 times 0.2 = 2 text V $.
simulate this circuit
Figure 2. The disconnected neutral wire turns live.
Also be aware that if the neutral conductor breaks and anything is plugged in to the circuit then the neutral wire may go live. Never assume that a mains conductor is at 0 V. Isolate properly.
answered Jul 21 at 8:12
TransistorTransistor
102k9 gold badges104 silver badges227 bronze badges
edited Jul 22 at 6:08
answered Jul 21 at 8:12
TransistorTransistor
102k9 gold badges104 silver badges227 bronze badges
answered Jul 21 at 8:12
TransistorTransistor
102k9 gold badges104 silver badges227 bronze badges
answered Jul 21 at 8:12
TransistorTransistor
102k9 gold badges104 silver badges227 bronze badges
102k9 gold badges104 silver badges227 bronze badges
$begingroup$
Is figure 2 an example of an incorrectly wired circuit? You aren't normally suppose to wire connections in a series like that right? Precisely due to the risk of the neutral going live.
$endgroup$
– Nelson
Jul 22 at 1:35
$begingroup$
@Nelson I'd say it's an example of a faulty circuit - i.e one where the neutral wire was broken, or indeed installed incorrectly. It wont work (light wouldn't turn on), untill the neutral is properly connected. What do you mean by "in series" here? This (with the neutral connected) is how it normally is - the lamp and the switch have to be in series, how else would it work?
$endgroup$
– JonasCz - Reinstate Monica
Jul 22 at 5:18
$begingroup$
Oh, ok, that makes sense. The open circuit caused by a broken wire, not someone deliberately putting a junction box there. That makes sense. A broken neutral will definitely shock if someone is stupid enough to grab the two broken wires of the neutral and complete the circuit.
$endgroup$
– Nelson
Jul 22 at 5:25
$begingroup$
@Nelson: I've added some text to Figure 2 to clarify. Since the transformer secondary is earthed one could get a shock by touching 'NEUTRAL' and earth. The body's capacitance to earth may be enough to shock even without a direct connection.
$endgroup$
– Transistor
Jul 22 at 6:11
2
$begingroup$
@Nelson It's not so much "someone is stupid enough to grab the two broken wires", but an example of what could happen to someone poking around the lamp socket, believing themselves "safe" in the knowledge that "the neutral is at zero volts" ... a break in the neutral anywhere from the lamp back to the distribution panel could expose them to the full mains potential.
$endgroup$
– TripeHound
Jul 22 at 10:54
add a comment
|
$begingroup$
Is figure 2 an example of an incorrectly wired circuit? You aren't normally suppose to wire connections in a series like that right? Precisely due to the risk of the neutral going live.
$endgroup$
– Nelson
Jul 22 at 1:35
$begingroup$
@Nelson I'd say it's an example of a faulty circuit - i.e one where the neutral wire was broken, or indeed installed incorrectly. It wont work (light wouldn't turn on), untill the neutral is properly connected. What do you mean by "in series" here? This (with the neutral connected) is how it normally is - the lamp and the switch have to be in series, how else would it work?
$endgroup$
– JonasCz - Reinstate Monica
Jul 22 at 5:18
$begingroup$
Oh, ok, that makes sense. The open circuit caused by a broken wire, not someone deliberately putting a junction box there. That makes sense. A broken neutral will definitely shock if someone is stupid enough to grab the two broken wires of the neutral and complete the circuit.
$endgroup$
– Nelson
Jul 22 at 5:25
$begingroup$
@Nelson: I've added some text to Figure 2 to clarify. Since the transformer secondary is earthed one could get a shock by touching 'NEUTRAL' and earth. The body's capacitance to earth may be enough to shock even without a direct connection.
$endgroup$
– Transistor
Jul 22 at 6:11
2
$begingroup$
@Nelson It's not so much "someone is stupid enough to grab the two broken wires", but an example of what could happen to someone poking around the lamp socket, believing themselves "safe" in the knowledge that "the neutral is at zero volts" ... a break in the neutral anywhere from the lamp back to the distribution panel could expose them to the full mains potential.
$endgroup$
– TripeHound
Jul 22 at 10:54
$begingroup$
Is figure 2 an example of an incorrectly wired circuit? You aren't normally suppose to wire connections in a series like that right? Precisely due to the risk of the neutral going live.
$endgroup$
– Nelson
Jul 22 at 1:35
$begingroup$
Is figure 2 an example of an incorrectly wired circuit? You aren't normally suppose to wire connections in a series like that right? Precisely due to the risk of the neutral going live.
$endgroup$
– Nelson
Jul 22 at 1:35
$begingroup$
@Nelson I'd say it's an example of a faulty circuit - i.e one where the neutral wire was broken, or indeed installed incorrectly. It wont work (light wouldn't turn on), untill the neutral is properly connected. What do you mean by "in series" here? This (with the neutral connected) is how it normally is - the lamp and the switch have to be in series, how else would it work?
$endgroup$
– JonasCz - Reinstate Monica
Jul 22 at 5:18
$begingroup$
@Nelson I'd say it's an example of a faulty circuit - i.e one where the neutral wire was broken, or indeed installed incorrectly. It wont work (light wouldn't turn on), untill the neutral is properly connected. What do you mean by "in series" here? This (with the neutral connected) is how it normally is - the lamp and the switch have to be in series, how else would it work?
$endgroup$
– JonasCz - Reinstate Monica
Jul 22 at 5:18
$begingroup$
Oh, ok, that makes sense. The open circuit caused by a broken wire, not someone deliberately putting a junction box there. That makes sense. A broken neutral will definitely shock if someone is stupid enough to grab the two broken wires of the neutral and complete the circuit.
$endgroup$
– Nelson
Jul 22 at 5:25
$begingroup$
Oh, ok, that makes sense. The open circuit caused by a broken wire, not someone deliberately putting a junction box there. That makes sense. A broken neutral will definitely shock if someone is stupid enough to grab the two broken wires of the neutral and complete the circuit.
$endgroup$
– Nelson
Jul 22 at 5:25
$begingroup$
@Nelson: I've added some text to Figure 2 to clarify. Since the transformer secondary is earthed one could get a shock by touching 'NEUTRAL' and earth. The body's capacitance to earth may be enough to shock even without a direct connection.
$endgroup$
– Transistor
Jul 22 at 6:11
$begingroup$
@Nelson: I've added some text to Figure 2 to clarify. Since the transformer secondary is earthed one could get a shock by touching 'NEUTRAL' and earth. The body's capacitance to earth may be enough to shock even without a direct connection.
$endgroup$
– Transistor
Jul 22 at 6:11
2
2
$begingroup$
@Nelson It's not so much "someone is stupid enough to grab the two broken wires", but an example of what could happen to someone poking around the lamp socket, believing themselves "safe" in the knowledge that "the neutral is at zero volts" ... a break in the neutral anywhere from the lamp back to the distribution panel could expose them to the full mains potential.
$endgroup$
– TripeHound
Jul 22 at 10:54
$begingroup$
@Nelson It's not so much "someone is stupid enough to grab the two broken wires", but an example of what could happen to someone poking around the lamp socket, believing themselves "safe" in the knowledge that "the neutral is at zero volts" ... a break in the neutral anywhere from the lamp back to the distribution panel could expose them to the full mains potential.
$endgroup$
– TripeHound
Jul 22 at 10:54
add a comment
|
$begingroup$
The neutral does not act like the live because the neutral is tied to ground at a single point somwhere.
You are imagining the neutral and live both move above and below each other about ground. Relative to each other, the neutral and live do move above and below each other. This is if you think of them in complete isolation relative to each other and only each other.
In the real world there are more absolute voltage potentials like ground or earth. If left to float, the live and neutral move together above and below some common-mode voltage. But in the real world we tie the neutral to ground for safety purposes. We don't want the live and neutral floating to whatever common mode voltage they feel like. The equipment probably wouldn't care and would still function since it only cares about what live and neutral are relative to each other, but it's dangerous to you (who is at ground potential) if their common mode voltage floats up to 1kV relative to ground.
Since the neutral is tied to ground somewhere, then the neutral becomes more or less fixed to ground. In that case, live line ends up doing all the movement above and below the neutral.
That said, you can still get shocked by the neutral if there is a load. The neutral is tied to ground SOMEWHERE but that somewhere might be quite far from where you are looking at the neutral. That means there is an impedance between where the neutral connects to ground and where you are looking at the neutral.
So if there is no load current then nothing disturbs that impedance and the neutral sits at ground. But if there is a load current, then the voltage developed across that impedance can be enough to have the neutral voltage rise above ground to shockable levels when there is a load current.
answered Jul 21 at 5:02
DKNguyenDKNguyen
10.2k1 gold badge11 silver badges36 bronze badges
$endgroup$
add a comment
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$begingroup$
The neutral does not act like the live because the neutral is tied to ground at a single point somwhere.
You are imagining the neutral and live both move above and below each other about ground. Relative to each other, the neutral and live do move above and below each other. This is if you think of them in complete isolation relative to each other and only each other.
In the real world there are more absolute voltage potentials like ground or earth. If left to float, the live and neutral move together above and below some common-mode voltage. But in the real world we tie the neutral to ground for safety purposes. We don't want the live and neutral floating to whatever common mode voltage they feel like. The equipment probably wouldn't care and would still function since it only cares about what live and neutral are relative to each other, but it's dangerous to you (who is at ground potential) if their common mode voltage floats up to 1kV relative to ground.
Since the neutral is tied to ground somewhere, then the neutral becomes more or less fixed to ground. In that case, live line ends up doing all the movement above and below the neutral.
That said, you can still get shocked by the neutral if there is a load. The neutral is tied to ground SOMEWHERE but that somewhere might be quite far from where you are looking at the neutral. That means there is an impedance between where the neutral connects to ground and where you are looking at the neutral.
So if there is no load current then nothing disturbs that impedance and the neutral sits at ground. But if there is a load current, then the voltage developed across that impedance can be enough to have the neutral voltage rise above ground to shockable levels when there is a load current.
answered Jul 21 at 5:02
DKNguyenDKNguyen
10.2k1 gold badge11 silver badges36 bronze badges
$endgroup$
add a comment
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$begingroup$
The neutral does not act like the live because the neutral is tied to ground at a single point somwhere.
You are imagining the neutral and live both move above and below each other about ground. Relative to each other, the neutral and live do move above and below each other. This is if you think of them in complete isolation relative to each other and only each other.
In the real world there are more absolute voltage potentials like ground or earth. If left to float, the live and neutral move together above and below some common-mode voltage. But in the real world we tie the neutral to ground for safety purposes. We don't want the live and neutral floating to whatever common mode voltage they feel like. The equipment probably wouldn't care and would still function since it only cares about what live and neutral are relative to each other, but it's dangerous to you (who is at ground potential) if their common mode voltage floats up to 1kV relative to ground.
Since the neutral is tied to ground somewhere, then the neutral becomes more or less fixed to ground. In that case, live line ends up doing all the movement above and below the neutral.
That said, you can still get shocked by the neutral if there is a load. The neutral is tied to ground SOMEWHERE but that somewhere might be quite far from where you are looking at the neutral. That means there is an impedance between where the neutral connects to ground and where you are looking at the neutral.
So if there is no load current then nothing disturbs that impedance and the neutral sits at ground. But if there is a load current, then the voltage developed across that impedance can be enough to have the neutral voltage rise above ground to shockable levels when there is a load current.
answered Jul 21 at 5:02
DKNguyenDKNguyen
10.2k1 gold badge11 silver badges36 bronze badges
$endgroup$
The neutral does not act like the live because the neutral is tied to ground at a single point somwhere.
You are imagining the neutral and live both move above and below each other about ground. Relative to each other, the neutral and live do move above and below each other. This is if you think of them in complete isolation relative to each other and only each other.
In the real world there are more absolute voltage potentials like ground or earth. If left to float, the live and neutral move together above and below some common-mode voltage. But in the real world we tie the neutral to ground for safety purposes. We don't want the live and neutral floating to whatever common mode voltage they feel like. The equipment probably wouldn't care and would still function since it only cares about what live and neutral are relative to each other, but it's dangerous to you (who is at ground potential) if their common mode voltage floats up to 1kV relative to ground.
Since the neutral is tied to ground somewhere, then the neutral becomes more or less fixed to ground. In that case, live line ends up doing all the movement above and below the neutral.
That said, you can still get shocked by the neutral if there is a load. The neutral is tied to ground SOMEWHERE but that somewhere might be quite far from where you are looking at the neutral. That means there is an impedance between where the neutral connects to ground and where you are looking at the neutral.
So if there is no load current then nothing disturbs that impedance and the neutral sits at ground. But if there is a load current, then the voltage developed across that impedance can be enough to have the neutral voltage rise above ground to shockable levels when there is a load current.
answered Jul 21 at 5:02
DKNguyenDKNguyen
10.2k1 gold badge11 silver badges36 bronze badges
edited Jul 21 at 18:27
answered Jul 21 at 5:02
DKNguyenDKNguyen
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answered Jul 21 at 5:02
DKNguyenDKNguyen
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answered Jul 21 at 5:02
DKNguyenDKNguyen
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As regards electricity, what matters is the potential difference (this is the reason why you need to touch two points to get shocked).
Usually, the neutral and ground are at the same potential and a simultaneous contact is harmless. On the opposite, touching the live and one of ground or neutral is to be avoided.
There can be faulty situations where there is a potential difference between ground and neutral (floating ground), even though the tension between neutral and live is normal.
answered Jul 21 at 15:42
Yves DaoustYves Daoust
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$begingroup$
As regards electricity, what matters is the potential difference (this is the reason why you need to touch two points to get shocked).
Usually, the neutral and ground are at the same potential and a simultaneous contact is harmless. On the opposite, touching the live and one of ground or neutral is to be avoided.
There can be faulty situations where there is a potential difference between ground and neutral (floating ground), even though the tension between neutral and live is normal.
answered Jul 21 at 15:42
Yves DaoustYves Daoust
1394 bronze badges
$endgroup$
add a comment
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$begingroup$
As regards electricity, what matters is the potential difference (this is the reason why you need to touch two points to get shocked).
Usually, the neutral and ground are at the same potential and a simultaneous contact is harmless. On the opposite, touching the live and one of ground or neutral is to be avoided.
There can be faulty situations where there is a potential difference between ground and neutral (floating ground), even though the tension between neutral and live is normal.
answered Jul 21 at 15:42
Yves DaoustYves Daoust
1394 bronze badges
$endgroup$
As regards electricity, what matters is the potential difference (this is the reason why you need to touch two points to get shocked).
Usually, the neutral and ground are at the same potential and a simultaneous contact is harmless. On the opposite, touching the live and one of ground or neutral is to be avoided.
There can be faulty situations where there is a potential difference between ground and neutral (floating ground), even though the tension between neutral and live is normal.
answered Jul 21 at 15:42
Yves DaoustYves Daoust
1394 bronze badges
answered Jul 21 at 15:42
Yves DaoustYves Daoust
1394 bronze badges
answered Jul 21 at 15:42
Yves DaoustYves Daoust
1394 bronze badges
answered Jul 21 at 15:42
Yves DaoustYves Daoust
1394 bronze badges
1394 bronze badges
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Neutral stays close to the same potential as 'earth' because they are shorted at your local power source.
The AC of live is plus or minus compared to neutral.
Regarding shock, consider that one end of 'you' is at same potential as earth (e.g. your bare feet on the ground). Then only if the other end is at a big enough potential difference away, THEN you experience a shock.
answered Jul 21 at 16:33
KripacharyaKripacharya
1758 bronze badges
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$begingroup$
Neutral stays close to the same potential as 'earth' because they are shorted at your local power source.
The AC of live is plus or minus compared to neutral.
Regarding shock, consider that one end of 'you' is at same potential as earth (e.g. your bare feet on the ground). Then only if the other end is at a big enough potential difference away, THEN you experience a shock.
answered Jul 21 at 16:33
KripacharyaKripacharya
1758 bronze badges
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add a comment
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$begingroup$
Neutral stays close to the same potential as 'earth' because they are shorted at your local power source.
The AC of live is plus or minus compared to neutral.
Regarding shock, consider that one end of 'you' is at same potential as earth (e.g. your bare feet on the ground). Then only if the other end is at a big enough potential difference away, THEN you experience a shock.
answered Jul 21 at 16:33
KripacharyaKripacharya
1758 bronze badges
$endgroup$
Neutral stays close to the same potential as 'earth' because they are shorted at your local power source.
The AC of live is plus or minus compared to neutral.
Regarding shock, consider that one end of 'you' is at same potential as earth (e.g. your bare feet on the ground). Then only if the other end is at a big enough potential difference away, THEN you experience a shock.
answered Jul 21 at 16:33
KripacharyaKripacharya
1758 bronze badges
answered Jul 21 at 16:33
KripacharyaKripacharya
1758 bronze badges
answered Jul 21 at 16:33
KripacharyaKripacharya
1758 bronze badges
answered Jul 21 at 16:33
KripacharyaKripacharya
1758 bronze badges
1758 bronze badges
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1
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i can get shocked by live even if there is no load due to parasitic capacitance , but why does nuetral not behave the same
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– Jyotir
Jul 21 at 5:00
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so that means if touch the nuetral(which i am not going to) it will still shock me.my main question here is why is nuetral 0 volt or ground
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– Jyotir
Jul 21 at 5:02
5
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You have a misunderstanding about voltage measurements.
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– DKNguyen
Jul 21 at 5:03
2
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please help me clear the misunderstanding
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– Jyotir
Jul 21 at 5:05
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In case someone thinks tldr; YOU CAN GET SHOCKED BY TOUCHING NEUTRAL
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– Huisman
Jul 21 at 6:06