Need to understand the neutral conductor

[isobunk]

Appreciate there are a lot or questions about this already but I just can't seem to grasp it so hopefully asking the question in my way will help.

Background: UK 240v AC domestic system.

As I understand it, if everything is wired correctly and there are no faults, I can touch the neutral conductor of a circuit and not get a shock.

Could I even touch the neutral bus bar in my consumer unit and not get a shock? Of course I am not considering to even try this but is this the case, even if there is load going through one or more of the circuits?

Could I break out the neutral wire from the main feed to my property before my consumer unit and grasp it?

I understand that on the live conductor of a circuit I have potential in the form of 240v and the neutral wire has zero potential.If I connect a load to this circuit that potential will flow from positive (240v) to the neutral conductor and operate the load e.g. a domestic light fitting.

So, lets say this is a very simple circuit:

[+240v]---[Switch]---[Lamp]---[0v]

1. If the switch is open (switched off), does touching the neutral wire after give me a shock?

2. What about if the switch is closed (switched on)?

If I extrapolate this circuit to lets say an electrified railway with an overhead wire. The overhead wire is the live conductor and the track is the neutral conductor.

I can touch the tracks and not get a shock. This would seem to be the case at all times when there is no fault. Let's say a train is on the tracks and switched off there is no shock. If the driver "switches on" the train and applies full acceleration drawing lots of current there is also no shock.

In this case the train itself is the load and it would seem that whatever position the power level is in the drivers cab there is no risk to me from touching the tracks.

But how can this be? If I make myself the load by touching the overhead conductor and the tracks I would get a nasty shock. In this case I am the load. If I was the load would someone else touching the tracks get a shock?

It almost seems like the introduction of a load "uses" (for want of a better term) the available potential and makes touching the tracks a safe thing to do. But is that true? Given my diagram above could I wire another load in series and have two lamps illuminated?

I guess this kind if makes some sense. The current flowing down the wire is a force, if that forced is turned into physical motion e.g. to turn a motor to move a train it would seem logical there is less of that force available to flow into the tracks.

Clearly I don't understand the concepts around this at all and I would welcome some guidance as to how this works.

Thanks.

 

[snowhead]

What has lead you to start thinking about the Neutral and want to learn more about it?
Are you training at the moment, or working in a related industry?

 

[isobunk]

I am working in a related industry. Access control. I am more involved in software but interested in how everything works.

 

[Megawatt]

I am working in a related industry. Access control. I am more involved in software but interested in how everything works.

Open your panel and touch the neutral bar but take a neutral loose with a load on it and grab it and touch the panel and see what happens. You will get bit

 

[dmxtothemax]

QUOTE - Could I even touch the neutral bus bar in my consumer unit and not get a shock?
Maybe.
if your instalation is bonded properly and grounded
then you should be able to touch the neutral bar.

 

[davesparks]

I understand that on the live conductor of a circuit I have potential in the form of 240v and the neutral wire has zero potential.If I connect a load to this circuit that potential will flow from positive (240v) to the neutral conductor and operate the load e.g. a domestic light fitting.

Voltage doesn't flow, current flows.
Voltage is a measure of the potential energy of a circuit, and it has to exist between two points, you can't have a voltage at a single point without having another point to be referenced to.

This potential dictates how much current will flow if a load is connected. For this it may help to consider the voltage as pressure, the greater the pressure the higher the flow.

A normal domestic supply has two current carrying conductors, the live and the neutral. At the substation transformer the neutral is connected to the earth via a network of earth rods. This earth connection keeps the neutral at the same potential as the earth, because the two are connected together they stay at the same voltage (slightly simplified as a small voltage difference can occur but that's not relative to this)
Everything that is then connected (by a connection with minimal resistance) to this neutral will then be held at the same potential as earth.
So if you touch the earth and the neutral at the same time then you are touching two points at the same potential and no current can flow.

 

[DPG]

It is important to understand the difference between touching a neutral conductor that is connected to the neutral bar (theoretically safe), and removing a neutral conductor from the neutral bar and touching it. Think about the current flow in the latter example.

 

[isobunk]

At the substation transformer the neutral is connected to the earth via a network of earth rods.

Ok, I had in my mind that the neutral returned all the way to the power station. But in reality potential can exist providing there is a reference point and earth is suitable for this.

So if I took the neutral conductor of my simple circuit (above) and stuck it into the earth in my garden would the lamp illuminate when the switch is closed?

It is important to understand the difference between touching a neutral conductor that is connected to the neutral bar (theoretically safe), and removing a neutral conductor from the neutral bar and touching it. Think about the current flow in the latter example.

So touching a conductor connected to the neutral bar is safe as theoretically be at the same potential as earth even though there is current flowing through it. I guess no current flows through me as I am at the same potential.

Touching a conductor that is not connected to the neutral bar, the current tries to find a path of least resistant to earth in this case through me.

Does that sound correct?

 

[davesparks]

Ok, I had in my mind that the neutral returned all the way to the power station. But in reality potential can exist providing there is a reference point and earth is suitable for this.

So if I took the neutral conductor of my simple circuit (above) and stuck it into the earth in my garden would the lamp illuminate when the switch is closed?



So touching a conductor connected to the neutral bar is safe as theoretically be at the same potential as earth even though there is current flowing through it. I guess no current flows through me as I am at the same potential.

Touching a conductor that is not connected to the neutral bar, the current tries to find a path of least resistant to earth in this case through me.

Does that sound correct?

The current does return to the power station via the neutral, through the substation and then via the national grid. The current don't flow through the earth, the neutral to earth connection holds the neutral at the same potential as the earth (and allows protective earthing to work)

Sticking the neutral conductor into the earth in the garden works in principle, however to make a suitably low resistance connection to the earth you would need to get a lot of metal in contact with the earth.

 

[DPG]

Touching a conductor that is not connected to the neutral bar, the current tries to find a path of least resistant to earth in this case through me.

Does that sound correct?

Yes, and it obviously isn't recommended that you do this!

 

[Lucien Nunes]

STart from first principles. A single-phase circuit needs two conductors - go and return. If you simply take these two conductors from the source of energy (typically a substation transformer) to the load, it will work because there is a circuit. Just like a 9V battery connected to a lamp, sitting on a wooden table. The two conductors are identical; neither is a neutral, no connection to earth is made.

The potential between these two conductors will be determined by the source (e.g. 230V) but the potential from either of them to earth is unknown. If the insulation is perfect then you could touch either conductor, since there is no circuit back from earth to the other conductor. However, especially on a public supply, you cannot tell whether the insulation of the whole supply system is perfect, and it probably won't be, therefore neither conductor is safe to touch, both must be switched, fused etc. If there is leakage or a short from one conductor to earth, it would go undetected, because the circuit will keep working.

It turns out that there are significant benefits, especially on a public supply, in connecting one of the conductors to earth at source. That forces the potential of that conductor relative to earth to be zero, thereby making it a neutral, and the other one to be 230V from earth making it a line. Leakage and faults can now be detected and disconnected automatically by before a shock occurs as these will immediately pass a current to earth, now that the return path from earth to neutral is established. There are many other benefits but the kettle has just boiled...

 

[Megawatt]

Ok, I had in my mind that the neutral returned all the way to the power station. But in reality potential can exist providing there is a reference point and earth is suitable for this.

So if I took the neutral conductor of my simple circuit (above) and stuck it into the earth in my garden would the lamp illuminate when the switch is closed?



So touching a conductor connected to the neutral bar is safe as theoretically be at the same potential as earth even though there is current flowing through it. I guess no current flows through me as I am at the same potential.

Touching a conductor that is not connected to the neutral bar, the current tries to find a path of least resistant to earth in this case through me.

Does that sound correct?

To help you understand you are right about touching the neutral to earth. That is your return wire

 

[eleclio]

This question reminds me of when I was an apprentice (40+ years ago).

Daft things I did as a boy

I got a light on my Test-Lamps from the back of a disconnected Ring-Main Socket neutral to the earth of the socket box. So thinking me kneeling on the floor was the same earth as the socket box I decided to touch one end of the test-lamps to neutral and the other end to my finger. Needless to say I never did that again.

I must have always have be destined to be a Spark. I also remember when I was about 8 yrs old we had an old broken bakelite switch cover where one of the Live terminals could be seen. I used to try and jump up in the air and touch the Live terminal and try and not get a shock. I always seemed to get that shock...............................