Vinay

“reponse” of human body to electric schock has been described by International Electrotechnical Committee in its report 60479.
Chapter 3 reports effects of AC while chapter 4 describes effects of direct current.
To summarize these two chapters, the risk of injury appears :
- if alternating current exceeds 35 to 40 mA (which explains the 30 mA tripping threshold standardised for protection against direct contact by means of RCD)
- if direct current exceed 150 mA.
Both these values under assumption the situation lasts more than one second.
In addition that same report mentions (§ 2.5.3) that impedance of the human body is higher to DC voltage than to AC voltage.

Now what is this comparison? Let the water connection of your washroom. Here the water initially stored in the overhead tank. Then through the pipe connection it reaches to the every taps in the washroom. When the taps are not opened still they contain the water inside the pipe. And they are ready to flow the water when the tap will open.

Further we consider the connection of the pipe can be made in two systems.

In the first system small pipes are connected with one big pipe and this big one is directly connected to the overhead tank.

In the second way consider all the pipes are directly connected to the tank.

Now you wish to go to the washroom and open a tap then the water from the tap will fall down. This water will reach to the drain.

If you open all the taps of the second system then there will be no disturbance in water flow in different taps. All they will give the water with full volume.

If you open one pipe in the first system then you will get the water in full volume. But when you will open all the taps simultaneously then you will not get the water from the tap with full volume. The nearest tap will give the more water than the far one.

Again consider in the second case one pipe has been broken down. Water from that pipe will fall down. But the others pipe are ok and there will no disturbance in their water flow.

On the other hand if one pipe breakdown in the first system it will disturb the other. And most of the case no water will flow in the other taps.

Now we consider a dc circuit. Here we have a dc source, which have a positive terminal and a negative terminal. This positive terminal is analogous to the overhead tank and the negative terminal is similar to the drain. The pipes here can be compared with the conducting path. In the case of a parallel circuit if one branch does not conduct it will not disturb the other branches. The second washroom is analogous to this parallel circuit.

In the first case the physical system represents the series circuit. Here if water flow in the main pipe is blocked then water flow in the others will off.

The overhead tank and the drain play the role of potential source. As the water goes down to the drain, the potential decreases.

Here the short circuit phenomena and the open circuit phenomena can also be explain. The level of overhead tank and the drain will be same if excessive flow (infinitive) in a branch makes the two levels equal. Then there will no flow in the other pipes because two levels are equal. And the open circuit phenomenon is simply the blockage of water in a pipe.