-1
$\begingroup$

If I have two 'hot' wires connected to a source and a load, and one of the wire is connected to the ground, this wire is called the 'Neutral'. But what happens if instead of using an additional wire to connect the 'live' wire to the ground, I use my body, I know that I would get an electric shock, but why, doesn't my body 'neutralize' the 'live' wire, just like a normal grounding wire that is connected to essentially make it 'neutral', causing no potential difference/voltage just like a regular 'neutral' wire?

$\endgroup$
1
$\begingroup$

I think grounding gets rid of the stray charge that builds up on something, making it neutral. But here, although the hot wire is neutral, it does have an alternating voltage coming from whatever generator it is connected to, which can certainly shock you.

This could be true in DC current as well, if the wire is connected e.g. to a battery. The battery generates a certain voltage, and the shock you get is not long enough to deplete the whole battery.

$\endgroup$
0
$\begingroup$

Let's say you have a transformer connected to an AC outlet. As long as neither of the terminals of the secondary is grounded, they, in theory, should have no voltage relative to ground. We can say that both terminals are hot in a sense they they have voltage relative to each other.

In practice, both terminals will have some voltage relative to ground due to a parasitic capacitance between the primary and the secondary, but, for the sake of discussion, we can ignore it.

Under such ideal conditions, either of the secondary terminals could be grounded with a wire and no current would flow through the grounding wire. You can "ground" it through your body and, under ideal conditions, no current would flow through your body either. When one of the terminals is grounded, the other, naturally, becomes hot relative to ground.

This, essentially, what is done at the secondary of distribution step-down transformers, bringing electricity to residential consumers. For instance, in North America, the secondary's center-tap conductor is grounded making it neutral. As a result, two other conductors (two phases) become hot relative to ground.

With that understood, it is extremely dangerous to touch any conductors associated with AC power, even if you believe that they are not hot. If you are curious about their voltage relative to ground, you can always measure it with a properly rated voltmeter.

$\endgroup$
  • $\begingroup$ But if no current flows how could we get 'electrocuted'? Doesn't touching the live wire makes it the same potential as the earth, thus no potential difference, and obviously no current, so how is 'shock' possible? (Or does the current only flow initially, then the voltage eventually becomes the same? ) $\endgroup$ – user212811 Nov 15 '18 at 10:55
  • $\begingroup$ @marshallbensin We get shocked when we touch live wire (and simultaneously touch ground), because the other wire, neutral, is grounded. $\endgroup$ – V.F. Nov 15 '18 at 12:22
  • $\begingroup$ No, what I mean is when you bring a wire and connect it to a live wire to the ground, it technically becomes neutral right? So what happens if that 'grounding' wire is replaced by a person with his feet on the ground? Doesn't the person somehow neutralize the live wire? $\endgroup$ – user212811 Nov 16 '18 at 0:50
  • $\begingroup$ @marshallbensin A person makes a poor grounding for the neutral. First to note is that, when such connection to ground of one of the wires is made, the only current flowing through the grounding person would be a leakage current due to parasitic capacitance I've mentioned, i.e., it would be pretty low current. $\endgroup$ – V.F. Nov 16 '18 at 2:54
  • $\begingroup$ @marshallbensin Second, if, with that grounding in place, another person touches the other wire, while also touching ground, both people will be electrocuted. This would be similar to two people holding each other's hands, and using their free hands to touch two live wires. Third, if we measure the voltage on that "neutralized" wire, it will be smaller than before grounding, since the leakage current would divide the voltage, induced from the primary side, between the parasitic capacitance and your body. Let me know what other scenarios you would like to explore. $\endgroup$ – V.F. Nov 16 '18 at 3:03
0
$\begingroup$

Yes, in a sense your body will neutralize the wire, but it does not mean that it will be safe for your body. Nor for any body else for that matter, as a human body is a poor conductor.

In an ungrounded installation you can say something certain only about relative voltages and currents between various points of the same circuit. But you cannot be sure about absolute voltages measured to the ground, nor to any circuit with which its not galvanically connected. It may be zero, it may be a few volts, or it may be thousands volts - depending on where the extra charge comes from. And it may come from a faulty insulation, circuitry, components, static electricity,induced by electromagnetic fields, radioactivity. ... you name it.

When you touch such a wire with a non - zero potential, and some part of your body is grounded then a current will flow through your body to neutralize the difference. If the voltage is large enough, it will cause an electric shock. This is also true for low voltage circuits. If you have a 5 V ungrounded circuit and it accumulates enough charge, it may happen that it's 'mass' will be at 100v above the ground, and the 'hot' wire will be at 105V. The circuit may work correctly, while it will still be dangerous. That's why proper grounding is so important: to protect users from electric shock, and possibly, circuits from being damaged by large currents caused by uncontrolled grounding.

Human body is quite a poor grounding, btw - it's resistance is about 1000 ohms (depending on connection points), while the proper grounding should be a small fraction of it. Preferably, a fraction of an ohm.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy