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Domestic circuit connection & fuse - Domestic circuit (Part 2)

Let's explore how the domestic circuits are connected (whether in series or parallel). Also, let's learn how the fuse helps protect the domestic circuits from voltage surges. This helps us explore why we have two separate circuits, one for low power devices (with 5A fuse) and one for high power devices (with 15 A fuse). Created by Mahesh Shenoy.

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Video transcript

in my house there are two kinds of switches once used for low-power devices like your TVs or mobile chargers or your laptops and everything and the other one for the high-power devices like your air conditioners or your refrigerators your geezers and and things like that I'm pretty sure the same thing exists in your house as well so the question is the question that I always had is why do we have two different kinds of plugs why can't we attach high-power devices over here it's advised not to do that but why well to answer this we need to see the complete picture of how all these sockets are connected together what is the kind of circuit that we have in our house which looks somewhat like this whoa whoa that looks was very complicated so you know what we'll do we'll start from what we already know and then build up from there okay so we've seen that for each plug point there will be three wires coming in so two wires come directly from the mains one is the live wire another one is called the neutral wire I'm not gonna write that because it's gonna get crowded as you've seen and the voltage difference between them is about 220 volts in India and of course we have one more wire which is a safety wire which is called the ground or the earth wire this wire carries any any current that is leaking off from devices due to any Falls ensuring that we don't get any shock so ideally it's not supposed to carry any current and we've talked about this in previous videos so if you need more details feel free to check that out but the thing is in our houses we don't have just one plug point we have many plug points and many devices and all of them will have these wires coming out of them and somehow all these must be connected together in some kind of a circuit so the first question we want to try and answer is what kind of connection do you think we'll be having and again to answer this we can start thinking from what we have already seen we have already seen two kinds of circuit connections that we can have we can have a series connection and we can have a parallel connection so you know what do you think is the kind of connection in our houses do you think it's a series or parallel or do you think it's a mix you know some are connected in CDs and some would be in parallel why don't you pause the video and just hear this a thought all right if you've given it some thought let's see let's start by exploring the series connection the series is when you connect them end to end right now one immediate problem you can see over here when two plugs are let's say connected in series is that if you were to close one of this switch let's say I put my mobile to charge over here and I close one of that switch no current will flow over here why because this switch is open see this is one single wire if you want the current to flow in this wire then both the switches need to be closed that means you need to switch on both these plug points in order order for the current to flow so either both will run or none of them will run that's how series works which means that's very inconvenient right I mean I don't know about you but I don't think I want my devices to work that way I want them to be independent of each other does that make sense and so if you put consider that in mind series is completely out of the options so we cannot have any devices coming in series so what does that leave us with that leaves us with handle connection so the way we can connect plug points to make them independent of each other is we connect them parallel across each other so that each of the plug point are connected with across the same points the live wire and then neutral wire so if you do it this way notice now I can close this switch and the current will run through that because this is one independent circuit it's independent of these a plug points and those switches so parallel is how all the circuits are connected in our houses and of course they would have their own grounds as well it's also super important and by the way if you're looking at this you're wondering what this this curve means it basically you know denotes that the ground and the hive are not connected to each other is this it's just a way of showing that they're independent wires it shows that one wire is going above the other that's it all right so this now might make you wonder does that mean every single plug point in your house and all the fans and all the devices get exactly the same voltage yes that's right every single plug point we get the same voltage that's the defining feature right and how much is that voltage as we said it's about 220 volt which is pretty high it's what makes these things dangerous and this might make you ask another question well does every single device require 220 volt what about your phone charges do they really need 220 volt well no in such cases you know what you will see inside those plug inside those adapters you will see small devices called transformers that can reduce the voltage if needed all right you learn about them in higher grades and everything don't worry about them okay the point is every single device every single plug point gives you 220 volts but not always that huh that's right you don't always get 220 volts because there can be fluctuations you might know about this there can be say lightning strikes or short circuits or overloading things that we'll learn about in future videos of course but because of all of these things voltages need not say the same sometimes you'll end up getting low voltage in which case your lightbulbs and your tube lights will glow little bit less your fans will be working a little slower which is a minor inconvenience not a big deal but what if sometimes you get a high voltage that's also possible due to fluctuations you might get say I know maybe a thousand volt which is totally possible what happens is then well then your device as we start drawing more currents if they are connected and then your devices can blow up that's one thing that can happen but there are more dangerous things that can happen you might know that if as the amount of current starts running through the wire as that amount increases the wire starts getting more and more heated up and if this wire is not designed to handle that current then that heating effect can actually melt the insulation exposing the live wires exposing these wires and they can go and touch other wires and cause all sorts of problems another thing that can happen is if the heat is too much it can even catch fire that's just the worst which means to safeguard ourselves let me just get back to normal to safeguard ourselves from this dangerous high voltage fluctuations we need to somehow make sure that if the current exceeds a particular value then the circuit disconnects somehow how do we do that well you might already know about that that's where if use comes in so this is what we call a fuse so what exactly is a fuse so what exactly is this fuse well a basic fuse is just a wire which has the ability to get heated up much quicker than the rest of the wires so as the as the current starts increasing in value it the fuse wire starts getting up heats getting heated up very quickly and after a point it's the fuse wire that immediately melts and as a result the contact breaks and this ensures that the entire you know the domestic circuit circuit in your house is disconnected from the mains and that's how it ensures safety and how do we build a wire like that with what are the properties of this wire if you are wondering well a couple of properties important properties would be one it needs to have a very high resistance compared to the rest of the wires why because a high resistance ensures more heating effect we have seen that before right as the current flows through any object if it has more resistance it will have more heating so that ensures more heating and to ensure that it melts quickly it will have low melting point so it also needs to have low melting point so with these two features a fuse wire can be built to protect our circuits and so now you may be wondering what's the maximum current this fuse wire can handle well that depends upon different kinds of fuse you can manufacture different kinds of fuses but the ones that you know the the low power circuits that we have in our houses those fuses can usually handle up to 5 amps of current if the current exceeds 5 amperes that fuse will melt so the idea is in this normal circuit like where your fans and tube lights are connected the current drawn is very low that means if the total current exceeds 5 amperes that means something unusual is happening and that's why this is design that way so this is what we would call a 5 amp circuit and of course you may be wondering hey I don't see these fuses in my house today where are they well today they are been they have been replaced by these new devices called circuit breakers they work on a very similar principle but yeah but over here they don't mess you don't have to change the wire every time of use blows up they just disconnect automatically okay a little bit more at once but the idea is the same so let's not let's not get into that so perfect right we have the fuse to protect us protect us from a high voltages we have the ground wires to protect us from some faults everything is fine but there's one problem what if I want to run my air conditioner and geezers and in refrigerators and other high power devices what will happen if I connect all of them and switch off or switch on all of them then together they will definitely draw try to draw more than five amps of current and the fuse will blow up for no reason right this was not unusual it is that high power devices can't run on this particular circuit which only limits to five amperes so what do we do what do you think we should do wells for that reason we will have a separate circuit for those high power devices so that's why those plug points which are responsible for which which provide power to high power devices will have you know we'll have a separate circuit so it will also have its own live wire it'll also have its own neutral wire it'll have its own fuse and we can now guess that this fuse can handle higher amount of current right so it turns out that this high power circuits usually usually handle about 15 amps of current so anything above 15 amperes then that fuse will melt so in our houses we will have two independent circuits one is 5 amps and another one is 15 amps and of course they should also have their own ground ground is definitely required so all these grounds will be connected together so will there be only two circuits or can there be more such circuits the answer is you can have many more circuits each one with their own fuse it all depends upon where you are staying how big the house is or whether it's a factory or things like that but usually they will be having 1 5 ampere circuit and one 15 ampere circuit so how do we how do we put this all together I mean there are only two wires one live and one u2 coming to the house so how do we distribute it in two different different circuits so the basic idea is we connect them all together so let me show you so we connect all the neutral wires together and we connect all the live wires together after the fuse and we put this in a box which is called the distribution box it because it's distributing the incoming wires in two different different circuits let me just write that this is called the distribution box distribution box and then this wire can now go out of your house and then connect to that electric pole but your electric company needs to needs to Bill you right they need to know how much electricity you're using it's for that reason it doesn't directly go it goes through an electric meter again something you may have seen and the basic idea behind this meter is that is the old ones is that you know there would be a disc and depending upon how much current you take how much current you're drawing the disc will keep on rotating and then there then they will just calculate the total number of rotations the disc has turned and that's how they calculate how much electricity have used and so from there we the wires will get connected to the mains through another fuse you might be asking why another fuse why not fuse is a safety device right so it doesn't hurt to have two levels of safety this will again be a higher level fuse higher amperage fuse so definitely more fuses at more levels means more safety and there we have it this is how our domestic circuit looks like hopefully this looks a little less complicated now all right so let's put it all together and see if we can recall some important things so my first question to you is can you recall what kind of circuits that we do we have usually in our house series or parallel or mixed circuits second question is why do we even use a fuse can you explain that to a friend and what are the two important properties of the fuse wire must have can you recall that and also why and lastly using these two can you now explain why we need to set maintain two separate circuits one for low power devices and one for high power devices if you have difficulty answering me you know any of these questions feel free to go back and check the video out again and I'll leave you with one bonus question why is the fuse always connected two live wires why can't we have a fuse with the neutral wire even there when the fuse melts the circuit breaks right so why is it always connect two live wires think about this