Why don’t we get shocked touching the negative terminal of an electrical source?

Why we are not getting shock when we touch negative terminal electrical source?

It depends on the potential difference between the terminal and the second terminal. If you source negative terminal with one hand the source positive terminal with your other hand there will be charge flow through your body. But what if the negative terminal is connected to earth ground and you touch your hands to the negative terminal and ground? There is no charge flow because there is no potential difference.

@ david: But in an 1p ac supply the neutral is always grounded and once I saw it practically by inserting one terminalof a table fan to the live phase and the other to ground . So by touching neutral we don't get shock. But a question arises here that how the negative cycle comes into play if neutral is always zero.

@Arulselvam: I have same question that david asked. That is During the negative cycle of ac supply, we are saying current flows from neutral to phase(Current reversed during negative cycle).

Perhaps things will be more clear to you if you think in terms of current rather than voltage.

Place an ammeter in the LINE and the NEUTRAL leads and you will AC measure current. This tells us that the NEUTRAL lead alternately sinks and sources current.

Or, place a current viewing resistor in the NEUTRAL lead, connect and oscilloscope and you will "see" current alternately sourced and sunk from the NEUTRAL lead.

David,
I have read & reread your explanation.
No doubt it's obvious the neutral alternately sources & then sinks current.
I also know I can touch the neutral & not receive a shock.
What I still don't grasp is why the driving potential when the neutral is sourcing is insufficient to deliver a shock. after all it's capable of driving a load.
Can you explain further for the dopes such as myself?

When sourcing/sinking current to the LINE there is a potential difference between the two. When trying to shock you there is no potential difference between NEUTRAL and earth ground, which you are referenced to. Now, touch one hand to NEUTRAL and your other hand to LINE and there is a potential difference across you and you will be shocked. Give it a try.

What if we only see the live phase with the help of oscilloscope?. It shows the negative cycles also. Its understandable if its a complete circuit connecting live, load and neutral and we connect the oscilloscope to the any point in the circuit. But how come the negative cycles in Live phase without the help of neutral?

The explanation about there being no Potential difference between Earth and neutral is correct, however in seeing bot cycles when you monitor the LINE or Live wire you may understand it better by thinking about what is actually happening in the conductor.
The Electrons that are moving flow at approximately 27 cm an hour in copper (thats just over an inch in US terms), so at 50 or 60 Hz the time they have to move is only around 20ms so they don't move far !! They are in fact only being shuffled back and forth over about 150um.
The electrons in BOTH conductors will be doing the same. The Negative cycle you are talking about is merely indicating a change of direction of the current. When the flow stops at the zero crossing point of the sine wave there os no Potential difference anywhere, but it will increase to maximum at the peak no matter what direction the current is flowing in.
Thats a lot to take in but hope it helps.

You must draw this in a diagram to understand. Draw a box and label it power source. Draw 2 lines out from this box and label one + and one - . Now draw a second box straight out from the first box. Label it load. Connect the + and - lines from power source to box. Now on the negative power source terminal draw a ground symbol. Imagine taking a meter and with the negative meter lead on negative or ground and the positive meter lead on + side of load take a measurement. It will read the value of the power source (voltage). Now take that positive meter lead and touch the negative or ground side of the power source. Both leads are at the same potential and so no current will flow. If you are standiing on ground and you touch the negative or grounded side of the power source you are also art the same potential so no current will flow. To get shocked there has to be a difference of potential between you and the power source. Do not do as one reply suggested to test by touching the positive side of the power source to get shocked or you will need somone to do CPR if the potential is high enough. This is a very simplified explaination. Do not think that you cannot get shocked by any negative side of a supply, just touch the power to your wired home phone, that is a -48 volts and it will shock you. The example I gave could also shock you if the power supply is not grounded and the negative side is floating at some potential above the ground you are standing on. Use a meter and not your body to find if you will get shocked or not or you may end up dead.