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Joined: Jun 2004
Posts: 7
L
Junior Member
In single phase current flow through phase and returned to neutral.when we touch the phase we fell shock but when touch the neutral we don`t,while current is also present in neutral.if we take the example of pipe and water,the water is present at every point of pipe,so please tell me why we do not fell shock in neutral?

Joined: Aug 2001
Posts: 7,520
P
Member
Hi Ali,

The reason is that in a system which is functioning normally the neutral has no, or very little potential with respect to earth.

On a normal supply the neutral side of the transformer is grounded. So the "hot" side of the line is at 120, 240, or some other voltage with respect to the earth. If you touch it while simultaneously in contact with the earth, you therefore have that voltage applied across your body and you feel a shock.

But even though current is flowing through the neutral, the only voltage present on it is a very small amount due to voltage drop along the cable. So you may have just 1 or 2 volts on it with respect to earth -- Not enough to shock you.

Joined: Oct 2001
Posts: 597
E
Member
Ali,

Following on Paul's last two sentences, look at this situation: [Linked Image from usfamily.net]
When the tool is working normally, the current flowing will be about 7 Amps. The circuit and its resistance can be shown by this diagram: [Linked Image from usfamily.net]
When the circuit works normally and 7 Amps is flowing, the touch voltage on the neutral will be:

(R4 + R6)* 7 Amps = 2.1 Volts. Too low to feel.

(R1 and R2 are so big, compared to R4 and R6, that they can be ignored to simplify the calculation; and R7 and R8 aren't present, cause the tool is working normally, that is, the hot wire hasn't broken loose and touched the grounded metal of the tool body.)

When the hot wire shorts to the tool body, and is not connected to the neutral, the current that flows is 188 Amps and all of a sudden, the person not only gets shocked, but because of the bad conditions (weather, mud, sweat) gets badly shocked. The circuit becomes this equivalent: [Linked Image from usfamily.net]


Al Hildenbrand
Joined: Jun 2004
Posts: 7
L
Junior Member
Thx very much both of U Paul and electrical.


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