Alternating Current Basics and Explanation of Shock
Lesson for Everybody
Forward: In this article I explain the Alternating Current Basics and how electrical shock can be got from Alternating Current.
By: Chrysanthus Date Published: 1 Sep 2012
Introduction
DC Circuit
A DC circuit is one where the current value is constant and flowing in one direction, continuously. A simple DC circuit consists of a battery, 2 conductors and a bulb. The positive terminal of the battery is connected to one conductor. The other end of the conductor is connected to a point at the bulb identified as the positive terminal of the bulb. There is another point of the bulb identified as the negative terminal. From this point the second conductor is connected to the negative terminal of the battery. Under that condition, the bulb lights. Assume that the circuit is on a board with the first conductor at the top (higher up vertically) and the second conductor at the bottom (lower vertically).
AC Current Illustration
Alternating Current is abbreviated, AC. Imagine in the above circuit that you reverse the connection of the battery; that is, you take the positive terminal of the battery and connect it to the conductor at the bottom and the negative terminal and connect it to the conductor at the top. There are certain bulbs that will still light with this new connection.
Current always flows from the positive terminal of the battery round the loop to the negative terminal of the battery. If you continue to reverse the connection of the battery, you will be sending current in opposite directions through the circuit. In the first interval current flows in one direction; in the next interval it flows in the opposite direction; in the next interval again it flows in the original direction; in the next interval that follows, it flows in the opposite direction; and so on. So the current changes or alternates direction as time goes on.
Note: in this demonstration the connections of the battery (and the resulting alternating current) is done by the hand.
I have illustrated alternating current above. In practice, the voltage source for an alternating current is not a battery. In practice an alternating voltage source alternates current automatically and the alternation is very fast. The alternation can be 50 times or more, per second.
One alternation (i.e. one forward and one reverse current flow) is called one cycle. In many cases the changing of current is not abrupt; it is smooth as follows: In one direction the value of the current starts from zero, then it rises continuously to a maximum value, then it descends continuously back to zero; immediately after that it changes direction and begins rising from zero. It goes to a maximum value and then begins descending again until it reaches zero; then it changes direction, again. This alternation is can be 50 or more times per second. Some alternations can be lower depending on the use of the AC current.
Frequency
The number of times the current alternates per second is called the Frequency. One alternation is called a Cycle. The time for one alternation to take place is called a Period. Frequency is measured in Hertz abbreviated, Hz.
The Mains
The rest of this article will focus on what is called the mains. The mains is the electrical supply in you house. The mains produces alternating current (AC). When you plug your TV cable to the socket of the wall, you are said to be plugging the cable to the mains. Some sockets have 2 holes while others have 3 holes. The third hole is the earth terminal (see below). In some cases the third terminal is not a hole, but a short piece of metal bar sticking out. Whether it is a hole or short piece of metal bar, it serves the same purpose (see below).
The word, mains, can also be used for water pipe or gas pipe. So what I am talking about here is electrical mains.
So, the socket in your house has 2 or 3 terminals. If it has 2, then the 2 form the alternating voltage source. If it has 3, then 2 form the voltage source and the third is the earth terminal (see below).
If the socket has 2 terminals then one has to be connected to the earth. Even though one is connected to the earth, it still carries current as well as the other one. If the socket has 3 terminals, then the third one is the one to be connected to the earth, by the house that has the socket. In this case the terminal connected to the earth does not carry current; the other 2 carry current.
In some areas of the developing countries, this convention may not be respected and so the risk of having shock is higher in the developing countries.
Shock
If you touch the conductor of an AC current you can have a shock if current from the conductor passes through you to the ground (or floor of your house). The current through you is the shock.
If 2 things are said to be at the same voltage potential, then current cannot flow from one of them to the other. If 2 things are at the same potential, the 2 things can however share the current that is flowing from that potential to a lower potential or share current that is coming from a higher potential. If they are part of the return conductor of the circuit, then they can share current that is going back to the voltage source.
If you are bare footed and you touch the terminal of a socket that is connected to earth, you will not have a shock, because you and that terminal are at the same potential. Even if current is flowing within the earth, current cannot flow through you. Remember, for current to flow, there must be a close loop. In this case, your body is not part of a close loop. If current is flowing within the earth, it is flowing in the earth to somewhere (a voltage source), it cannot be flowing arbitrarily.
If you are bare footed and you touch a terminal of the socket that is not connected to the earth, you will have a shock. This is because that terminal and the ground are not at the same potential. So current flows from the terminal potential, through you to the ground. From the ground, it goes to the voltage source that supplied the current. For current to flow, there must be a close loop. It is not all the time that you will be able to work out how the loop is close. What you should always bare in mind is the difference in potential, especially when it comes to shock.
The cable from your TV set or radio set, to the socket is called the mains cable. It may have 3 or 2 conductors inside. Inside, the conductors are separated by insulators, so that they are not touching. If they touch, there might be short circuit (see later). Each conductor in the cable is at the same potential as the corresponding terminal connected to, at the socket. So, if somehow the cable is scratched and you touch a conductor of the cable that is not at the earths potential, you might have a shock.
Electricity Company Cable
The electricity company cable that comes to your house from outside, should be treated in the same way as the mains cable that is connected to your TV set. This cable from outside is connected to all the sockets of your house. I will not explain how the connection is made, but just accept that there are connections from the cable from outside to all the sockets of your house.
AC Load in the House
For the DC circuit above, the bulb is called load. Anything that consumes the power of an electrical circuit is called the load. The bulb shines, so it consumes electrical power. For the mains, the load is all the electrical appliances in your house connected to the sockets. Each socket has its own load connected directly to it.
The following table gives the mains voltages and their frequencies in some countries:
Country - Voltage - Frequency
Australia 230V - 50Hz
Canada 120V 60Hz
France 230V 50Hz
Germany 230V 50Hz
Ghana 230V 50Hz
India 230V 50Hz
Japan 100V 50Hz and 60Hz
Russia 220V 50Hz
South Africa 230V 50Hz
Spain 230V 50Hz
Switzerland 230V 50Hz
United Kingdom 230V 50Hz
U.S.A 120V 60Hz
Root Mean Square Voltage
The AC voltage is not really the same as the DC voltage. The AC voltage is called the Root Mean Square Voltage. Root Mean Square is abbreviated, R.M.S (or r.m.s or rms). For now do not worry about the difference between the 2 voltages.
That is it for this article. I hope you now know the meaning of AC current and the role it has in your house. A word of advice: avoid touching any electrical cable conductor (or socket terminals) of a cable in your house. This is to avoid shock. If you have any problem with the electricity of your house, call an electrician. If you have any problem with an electrical appliance in your house, call the relevant technician. This is because I have not explained to you how to identify which conductor is earthed and which is not earthed. I have also not explained how to detect whether the house is earthed or not. These two explanation are best reserved for the technician or engineer, for security (avoiding shock) reasons.