hi friends we are all using electricity in our homes but do you know where the electricity comes from how is it supplied to our homes how are the electrical connections done in our home what is earthing and the safety devices used in our homes we'll be discussing all these practical things in this video on domestic electric circuits I'm sure after watching this video you'll become an expert in domestic electric circuits and when the electrician comes to your home you know what to discuss with him let's start with how do we get electricity at our homes electricity is being generated at some power station which is usually far away from the city the bar station has an electric generator that produces a massive amount of electricity the electric bar is generated at a very high voltage of about 11 KS that's 11,000 000 volts the generated electricity is transmitted from the Power Station through long electric cables now we know that from Jewel's law of heating that when current flows in the wires heat will be produced so some energy will be lost in the form of heat the heat loss is directly proportional to the square of the current so if you want to minimize the heat loss the current should be very small to reduce the current the voltage is increased using a Transformer before the transmission the voltage is typically stepped up from 11 K to a much higher voltage of 132 K using a stepup Transformer the electric bar is transmitted to the main substation using long electric cables at the main substation the voltage is stepped down from 132 K to 3 3 KS using a Step Down Transformer at the intermediate substation the voltage is stepped down from 33 KT to 11 KT and finally at the city substation the voltage is stepped down to a much lower value and is supplied to our homes in India the voltage that we get in our homes is 220 volts in United States the voltage is 110 volts did you know that the voltage or the current that we are getting is alternating in nature the polarity keeps on changing that's why it's called alternating current the electricity comes to our homes through two thick insulated wires one of these wires is called the live wire or phase wire and the other wire is called the neutral wire the live wire in India has the potential of 220 volts and the neutral wire has the ground po potential of 0 volts so what is the potential difference it's going to be 220 minus 0 that is 220 volts the two insulated wires live and neutral wire enter a box fitted in the house in this box a main fuse is put on the Live Wire this fuse acts as a safety device and has a high rating of about 50 ampere or even more the two wires then enter the electricity meter the meter is installed by the city's electricity department and it records the amount of electrical energy consumed in the house what is the unit used by the electricity meter that's right kilowatt R because kilowatt R is the commercial unit of electrical energy the two wires coming out of the electricity meter are connected to a main switch the main switch can be used to turn off the electrical supply for example when repairing some electrical faults the main switch is a double pole switch because it breaks the connection of the live and neutral wires simultaneously from the main Supply after the main switch there is the distribution box from the distribution box the wires go to the different parts of the house the distribution box looks something like this and it has many mcbs MCB stands for miniature circuit breaker mcbs are safety devices like fuses and we'll look at these in detail later in the video there are so many mcbs in the distribution box since each MCB is for a separate circuit in the house if I switch off the mcbs the power supply in the house is cut off and when I switch it on again the power is back I'm sure you've noticed that there are two type of electrical sockets in your house small sockets like these and large sockets like these do you know why because there are two types of circuits in a house a lighting circuit and a power circuit the lighting circuit allows a maximum of 5 ampere current and is used for low power rating devices such as bulbs fans and is also connected to the small socket in the house that's why for the lower power rating appliances like televisions computers we use the small sockets in the house the power circuit allows a maximum of 15 amp current and is connected to the large sockets in the house that's why we use the large sockets for high power rating devices such as electric iron heater geizer and refrigerator each distribution circuit has a separate fuse or MCB so that if there's a fault in one circuit the other one will remain unaffected these distribution circuits are connected in parallel some of the distribution circuits are lighting circuits and they have a 5 a MCB or slightly higher a 6 aamp MCB some of the distribution circuits are power circuits and they usually have a 15 aamp or a 16 aamp MCB we discussed about the live and neutral wire do you know that there's also a third wire in the house called the Earth wire the Earth wire is connected to the Earth Connection in the house the Earth connection or local earthing is done near the electricity meter of the house a hole about 2 to 3 m deep is dug in the ground and a copper Rod is inserted in the hole the end of the copper Rod has a thick copper plate and it is buried in the ground the plate is surrounded by a mixture of charcoal and salt to make a good contact between the plate and the Earth the upper end of the copper Rod is joined to the Earth connection at the electricity meter the goal of local earthing is to provide a safety mechanism for example if due to some fault such as short circuiting an excessive current flows through the wires then the excessive current will pass through the Earth wire if there is local earthing but if there's no local earthing done then the wires in the house may get overheated and it can cause fire as we discussed there are three wires in the house Live Wire neutral wire and Earth wire if you look at this plug you can see that there are three wires of different colors coming out of this plug the plastic insulation of these wires is of different colors the red wire is the Live Wire the black wire is the neutral wire and the green wire is the earth wire this is the old convention the new convention is brown color is used for the Live Wire Light Blue for the neutral wire and green or yellow for the Earth wire this color coding helps to distinguish between the different wires let's place the old and new color coding for the live neutral and Earth wire on our concept board all the three wires live wire neutral wire and Earth wire are going around the house and to each room let's say there's a light bulb in the room how is the light bulb connected to the wires one end of the bulb holder is connected to the live wire and the other end is connected to the neutral wire here the Earth wire is not used the switch is always connected to the live wire now if another bulb is there in the room it will be connected in a similar way are the two bulbs in series or parallel that's right the bulbs are in parallel the advantage of parallel connection is that both the bulbs get the full Voltage 220 volts in this case and they can glow brightly at the full Voltage also if one of the bulbs gets fused then the other bulb will continue to work but if you connect the bulbs in series then the voltage will get divided between the bulbs and they will not get the full voltage and if one of the bulbs gets fused then the other bulb will also stop working that's why everything in the house from lights fans televisions to the refrigerator they are all connected in parallel next let's look at how the three pin sockets in the house are connected the three pin sockets have three holes the upper and bigger hole in the socket is for the Earth connection the hole on the right side is for the connection to the live wire and the hole on the left side is for the connection to the neutral wire in the three pin plug the top pin is for the Earth connection the pin on the left is for the live connection and the pin on the right is the neutral pin as you can see the Earth pin is thicker and longer than the other two pins why the Earth pin is made long so that the Earth connection is made first this ensures safety before the live and neutral pins are connected the Earth pin is thicker so that it cannot accidentally be put into the live or neutral hole of the socket when a three-pin plug is inserted into a three-pin socket all the three connections are made live neutral and Earth connection we know that the live and neutral wires Supply the potential difference to the Appliance in India the potential difference is 220 volts now let's see how the Earth wire is used for earthing an appliance let's consider an electrical Appliance like an electric iron or an electric kettle due to wear and tear or excessive heating the plastic insulation of the wires gets removed or burnt as a result the naked Live Wire May touch the metal body of the appliance this is dangerous because now the whole metal body of the appliance is at 220 volts so if it touch the appliance we'll get a bad electric shock to avoid the risk of electric shocks for safety the metal body of the appliance is earthed earthing is done by connecting the metal body of the appliance to the Earth wire so when the three- pin plug of the appliance is put in the three in socket the connection with the Earth wire is also made now if there's any fault in the appliance and by Chance the Live Wire touches the metal body of the appliance but since the appliance is earthed the current will pass directly through the Earth through the Earth wire the current will not pass through our body and so we won't get an electric shock the earthing of electrical appliances is used as a safety measure and it prevents us from getting a shock earthing is usually done for electrical appliances that we touch and they draw High current what are some examples electric iron electric kettle refrigerator washing machine microwave oven electric bulbs and tube lights are not earthed since we don't touch them when they are switched on so next time when you're using an electric electrical Appliance and you feel an electric shock when you touch the body of the appliance to remember to have the wiring of the appliance checked and also the earthing of the appliance once the fault is fixed you should not feel an electric shock when using the appliance let's put earthing on our concept board now let's discuss about the situation when due to some fault an extremely large current can flow in the domestic wiring this can be very dangerous since the large current produces a lot of heat and it can start a fire let's understand what can cause the high current and the safety measures to prevent it an extremely large current can flow in two situations when there is short circuiting or when there is overloading let's first discuss short circuiting if the plastic insulation of the live wire and neutral wire gets toned then the two wires will touch each other this touching of the live and neutral wire directly is known as Short Circuit the wires are made of copper and are good conductors of electricity so when the two wires touch each other the resistance of the circuit will be very very low as a result the current flowing through the wires becomes very high this will cause overheating in the wires and it can lead to a fire overloading is another case where a large amount of current May flow through the domestic wiring when does overloading happen let's say in a house two or three air conditioners a water heater an electric iron and a washing machine are all being used at the same time when too many electrical appliances of high power rating are switched on then a very high current is drawn in the wires this is is called overloading overloading can also happen if many electrical appliances are connected to one single socket in overloading when the high amount of current flows through the household wires it causes overheating in the wires and it can lead to a fire do you know what safety devices are used to prevent fire during short circuiting or overloading that's right safety devices such as the electric fuse and MCB miniature circuit breaker are used first let's discuss the electric fuse the electric fuse is made of a thin wire of short length the wire is usually a tin plated copper wire or an alloy of tin and lead and it has a low melting point when a short circuit or overloading takes place the current becomes very large this heats up the fuse wire a lot lot the melting point of the fuse wire is much lower than the copper wires so the fuse wire melts and it breaks the circuit the electrical supply is cut off this prevents damage to the wiring in the house or the appliances in the house so the electric fuse works on the heating effect of current the fuse or MCB are typically fitted just above the main switch and in the distribution box in the house let's discuss the properties of the fuse wire is the fuse wire thin or thick that's right the fuse wire is thin why because a thin wire will have a higher resistance due to the high resistance the fuse wire will get heated up easily and melt fuse wires are made of different thickness depending on the maximum amount of current it allows for example a fuse wire of rating 5 aamp allows a maximum of 5 aamp current and it will melt if the current goes higher than this a 5 aamp or a 6 aamp fuse is typically used for the lighting circuit in the house where the maximum current should be around 5 aamp now what should be the fuse rating for the power circuit in the house that's right 15 aamp or a bit higher say 16 aamp so the fuse wire for the 15 aamp fuse will be thicker than the fuse wire for the 5 aamp fuse as we discussed fuse is a safety device which protects the wiring in the house from issues such as short circuiting and overloading now what should you do if the fuse in the house blows you should immediately call the electrician so that he can investigate why there was a large amount of current that cause the fuse to blow only after the issue has been found and fixed the blown fuse should be replaced with a new fuse these days the electric fuse that have a fuse wire are being replaced with a new type of device known as mcbs MCB stands for miniature circuit breaker and it looks something like this when the current becomes large the MCB puts off the switch like this and cuts the Electric Supply once the fault has been corrected the MCB can be reset like this advantage of MCB is that it does not have to be replaced it can be reset by simply flipping the switch do you know how an MCB works the MCB contains an electromagnet when the current becomes High the electromagnet becomes strong enough to pull and turn off the switch this breaks the Sur circuit and protects the wiring and appliances in the house so the MCB works on the magnetic effect of current and the electric fuse works on the heating effect of current we have discussed about the fuse and MCB which are used in the main fuse or in the distribution box of the house fuses are also used to protect individual appliances that may get damaged due to an excessive current flowing through them appliances such as refrigerator television have their own fuses that protects them against damage from high current for example a television that uses 1 ampere of current typically has a fuse of rating 2 ampere this fuse will protect the television from a current higher than 2 aamp these fuses can also be found in power strips that have surge protection this type of fuse is known as a cartridge fuse as you can see there is a thin fuse wire in this glass tube if there's a large current then the fuse wire melts and breaks the circuit this protects the appliance that is connected to the par strip from getting damaged once the fault is fixed the cartridge fuse needs to be replaced the cartridge fuse is cheap it costs about 10 Rupees and it can save your appliance that may cost cost thousands of rupees the cartridge fuse acts as a safety device and works on the principle of heating effect of current let's Place short circuiting and overloading on our concept board let's also put the safety devices the electric fuse and MCB which are used as protection from these issues on our concept board I hope the concept of domestic electric circuits is crystal clear to you now now you can be an expert and when the electrician comes to your house you can discuss these things with him and do remember to like comment and share out this video and if you haven't subscribed to my YouTube channel hit the Subscribe button right now be sure to click the notification Bell to get notified about new videos and do check out my website Manoa academy.com for more videos like these and for the quiz and the top three questions on this video thanks for watching