By ghosts_in_the_code

2015-09-25 14:59:36 8 Comments

In domestic electrical circuits, there are 3 wires - live, earth and neutral. What is the difference between the live and neutral wires?

As there is AC supply, it means that there are no fixed positive and negative terminals. Current rapidly switches direction. Does that not mean that both the live and neutral wires carry the same amount of current, alternatively? Why is the neutral wire called 'neutral'?


@adsp42 2018-11-06 22:36:25

What is the difference between the live and neutral wires?

The Life wire has a voltage (220V effective, in EU ) whereas the neutral is zero volts, at least in theory (unbalanced circuits could see some voltage on neutral, but that's undesired)

Does that not mean that both the live and neutral wires carry the same amount of current, alternatively?

Correct, when switched on. But then the "alternatively" is only misleading here. If you mean alternative current as in AC/DC, then yes. Of you mean some time on live wire, then on neutral, then no.

Why is the neutral wire called 'neutral'?

This is in the context of a star circuit (Y) which is a three-phase circuit and all the consumers are considered in theory balanced so that the neutral will carry the sum of all three phases and that is 0 volts.

@Guill 2018-01-06 23:09:59

Live, neutral,and earth, are labels that are used to convey some information on the use of each wire.
You are correct in thinking that in a typical two wire AC loop/circuit, both wires carry the same amount of current (amps). So, both wires could be considered live wires.
In a 3 wire circuit, the neutral wire is created when you have a power source that is center tapped (CT), thereby creating two loops that are 180 degrees out of phase with each other. For example, when you have 220V center tapped, each loop is 120V with respect to the CT. If each loop has the same load (current), then the CT current is zero. Because of this, the CT wire is called neutral wire (even when it carries some current).
Because of safety concerns, the neutral wire is grounded at the mains panel, and the grounding wire is called earth because it is physically grounded to earth (via water pipes or metal rod). To sum up, a live wire carries the full load current, while a neutral wire carries some current, only when the loads are not balanced.

@rghome 2017-12-04 10:10:30

The voltage on live and neutral varies depending on country and even within a country on the location. Neutral is not necessarily zero and assuming it is will likely get you electrocuted.

The general idea is that live supplies the voltage and neutral is the return wire.

In most installations the live is at the required voltage and the neutral line is connected to ground at some point (so zero volts relative to ground). But neutral is also connected to the live wire through the device being powered, so the voltage close to the device won't be zero if the device is on.

However, it is not uncommon in Europe for both live and neutral to carry a voltage relative to ground (for example, 130v), obviously with different phases giving approximately a 240v supply relative to each other. In this case, you may see a fuse on both the live and neutral wire and you will get a shock from both, even if no device is plugged-in or switched-on to complete the circuit. My own house is like this.

@Cees Timmerman 2018-08-02 00:22:27

So in the USA, the live wire pushes and pulls electrons into/out of the ground, and the neutral is the normal ground connection of your device? (Ground being the abnormal one connected to the device shell.)

@rghome 2018-08-02 07:28:34

Yes - that is normal almost everywhere, but there are exceptions. See this page: It states: "Also in some places in Belgium three phase 220 across the phases (= 127 phase to earth/neutral, 230V Y output on transformer) is used on older domestic dwellings (new installations are 400/230V 3 phase, neutral, earth). For this reason all Belgian fuseboards (whether actual fuses orcircuit breakers) protect both current carrying wires irrespective of supply type."

@joshua minnies 2016-02-29 19:36:29

You can either understand the concept of the neutral wire mathematically or practically. Since I'm more of a practical guy,let's take a look at the bigger picture. There is no neutral wire coming from the generator nor in transmission systems. The neutral wire is only implemented at the distribution (4-wire systems) and reticulation (live and neutral.... And earth) end of the picture.

Why is this you may wonder. The reason is that at the generator and transmission level, the lines or conductors have near identical impedance (ideally identical) therefore, the voltage between each of the 3 lines are of the same magnitude but 120 degrees apart from each other in phase. At the distribution level, your loads are far from identical, in fact each time a consumer of electricity switches the light on, the entire impedance of the distribution network changes.

This means that without a neutral wire, the voltage accross each load and the voltage between phases would be different, which is not ideal for both the consumer and the electrical system as it results in an imbalance of the electrical distribution system. Loads with greater impedance would require a larger volt drop across them than loads with less impedance. The effects of this can be devastating on equipment not designed to handle the changing of the supply voltage, not to mention, your lights would fluctuate between dim and the sun like a disco club. This is where the neutral wire comes into play. The neutral wire is connected at a common point to all three phases. Ideally at $0\,V$ e.g star configuration.

This ensures that if there is a difference between each phases load impedance, that the voltage is kept constant. Which is why you only have $220\V$(RMS) and $110\,V$ (RMS) or other standard voltage levels. It's the electrical current that should always be made capable of fluctuating. With the neutral implemented, we get constant voltage accross any load(impedance) with varying current.

How does the neutral wire make this possible? Since the neutral wire is a potential between all three phases, each phase along with the neutral wire can form an independent circuit e.g your house, hence live and neutral. It is the role of the neutral wire to carry any current as a result of the imbalance in impedance of each of the phases loads. This results in the maintenance of a stable standard voltage rating. Remember that voltage is relative to another voltage level.

If $220\,V$ is high, neutral is on the other hand low, which also means that since there is this potential difference, an electrical circuit may be formed in the first place.

Now, to answer the question posed in this topic, the live wire that can be traced back all the way to the nearest transformer(s) whose phase wires can be traced back to the generator's stator winding all the way at the power station. Neutral is the wire tied at the low potential end between each phase, enabling the completion of a circuit and maintaining a stable voltage level.

Since the neutral wire completes and electrical circuit (in terms of alternating current) it carries the same current as the live or phase wire tracing back to the generator, however, it's potential to earth is nearly $0\,V$. The voltage between the phase to earth would be $220\,V$, so the phase wire would alternate current direction between maximum positive and maximum negative peaks of the AC cycle.

@Cees Timmerman 2018-08-02 00:13:51

If its potential to Earth is nearly 0 V, then why is it unsafe to touch a neutral wire?

@Steve 2019-05-19 23:53:37

@CeesTimmerman, firstly because the neutral conductor may not be at exactly 0V relative to ground, and secondly because wiring errors during installation may mean the conductor identified as neutral is in fact the live conductor - the nature of AC means that equipment will almost always work regardless of the wiring configuration, so the error will not normally be apparent.

@user107243 2016-02-14 07:51:06

Live: 220 V

Neutral and earth: zero.

@Danu 2016-02-14 09:23:19

This should be a expanded a little: Add some explanation, instead of just a brief statement.

@Cees Timmerman 2018-08-02 09:19:05

I tried to expand it a little by noting that the voltages are relative to the ground, and that the neutral and ground wires are at ground voltage while not connected to live (typically through a device).

@DELTA12 2016-01-17 11:23:22

The live wire oscillates and either drains or supplies electricity to the neutral wire. The live wire oscillates between 230V to -230V and the neutral wire always stays 0V.

@Norbert Schuch 2016-01-17 14:09:56

0V relative to what?

@DELTA12 2016-01-17 14:24:18

Voltage isn't relative to anything.

@Norbert Schuch 2016-01-17 14:36:58

Voltage is a difference between two potentials, so you always need a reference point (i.e., the one which you call "0V").

@Ján Lalinský 2016-01-17 15:01:00

"the neutral wire always stays 0V." that is close to truth, but I think that, depending on the state of the close-by electrical network, the neutral wire may be several volts off the 0 V potential assigned to ground. Also, the value $U = 230 \text{V}$ is effective voltage of single phase supply, not its amplitude. The amplitude of voltage oscillation is actually $U_{max} = \sqrt{2}U$ = 325 V.

@docscience 2016-11-28 04:15:56

@JánLalinský neutral can be off zero if the load connected to the generator phases is unbalanced. Slight differences in load reactance can result in the three phases being slightly off and not perfectly adding up to zero. This can lead to residual AC current flowing through neutral. In a well balanced connection the residual may only be millivolts.

@SchrodingersCat 2015-09-25 15:49:53

What is the difference between the live and neutral wires?

LIVE WIRE The live wire is connected directly to the generators of the electricity supply company.It carries current at high voltages (about $220-230\,\mathrm{V}$).

NEUTRAL WIRE The neutral wire returns the electricity to the generator after it has passed through the appliance.The neutral wire completes the circuit.The neutral wire is at approximately $0\,\mathrm{V}$ but to be safe you must NEVER touch this wire either. If the wiring is faulty it may be carrying the same electricity as the live wire.

Does that not mean that both the live and neutral wires carry the same amount of current, alternatively?

Yes,they do. As I have mentioned above. The live wire carries the current towards domestic appliances and others instruments and the neutral wire emerges from the appliance and carries the current back to source.

Why is the neutral wire called 'neutral'?

Basically it is so called as it is at $0\,\mathrm{V}$. Nothing else.

@SchrodingersCat 2016-01-18 14:50:18

Reason for the downvote???

@Norbert Schuch 2016-01-19 21:24:22

"The neutral wire returns the electricity to the generator" -- there is no difference between the two wires except that one has the same potential as earth. Regarding their role in "transport of electricity", they are completely identical.

@tfb 2016-02-29 20:38:17

Please do not say that the neutral wire is at 0V: while it is more likely to be close to 0, it is not nearly likely enough that you would want to touch it, for instance.

@dominecf 2016-02-29 20:46:11

The live wire is not directly connected to the generator; there are several transformers and a circuit breaker inbetween. The generators make typically several kilovolts. You do not wish to connect your home appliances to the generator. 220 or 230 (or 240 or whatever) is formally not high voltage. Also the notion of alternate current going always from the source to the load is, at least, confusing.

@Vinayak 2015-09-25 15:45:33

The neutral is always at zero potential and it is taken as a reference. It is from this reference we mark the voltage at live wire. In short keeping the neutral always at 0, the potential at live wire varies.

Now, the earth wire is another neutral at zero potential. It is nothing but a wire connected to earth on safety lines.

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