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## Class 10 Physics (India)

### Course: Class 10 Physics (India)>Unit 4

Lesson 8: Domestic circuits

# Live wire, neutral & ground (earth wire) - Domestic circuits (part 1)

The live wire of domestic circuits is usually red and is at high voltage. The neutral wire is black and has voltage close to that of the ground. The potential difference between these two wires in India is about 220 V. The earth or ground wire provides safety against faults and current leaks. Earth pin is longer to ensure earth connection happens first while connecting and last while disconnecting any devices. Created by Mahesh Shenoy.

## Want to join the conversation?

• Will you get a shock touching the live wire even when the switch is off?
(5 votes)
• Appliances become live if the live wire touches the case. ... Even if a circuit is switched off , the live wire can still be dangerous. If you touch it, you may complete a circuit between the live wire and the earth ! - because you'll be standing on the floor, so you’ll get a shock.
(6 votes)
• we know that the neutral wire has approximately the same voltage as the ground therefore its neutral. Then why the neutral wire don't act as a ground/ earth wire?
(4 votes)
• Hi ! The neutral wire just has it's voltage the same of Earth , but it can't be connected to ground as voltages of ground and wire will be same the electricity won't flow (As their potential difference is equal ) . Making it simpler it's like connecting two tanks having same amount of water in same height and expecting the water to move from one to the another (which isn't possible)
(4 votes)
• what will happen when we pass a slight current into the live wire and touches the green wire which is disconnected from the earth?
(3 votes)
• Then we will have a shock as the live wire's current flows through ground wire which is not connected to ground
(3 votes)

## Video transcript

here's a seemingly boring plug and a plug point something that we see every day right but here's an interesting question if you looked at your plug carefully you will see that the top of the top pin is usually longer and thicker compared to the other two pins why do you think that is the case turns out that this can save us from deadly shocks but how you may be wondering how can a little feature like making one pin longer can save us from shocks well to answer that question we need to explore what are the different wires that come to your plug point and what each wire does so that's what we will do in this video we'll explore these three wires and then hopefully we'll be able to answer the original question so let's begin a wire that comes from one of these bottom holes one of the wires will be insulated with a red color and the other one would be insulated with a black color the red wire is often called the live wire so this is live or it's also called the hot wire and we'll see in a while why it's called that way and the black wire is often called the neutral wire so the immediate question could be why are they didn't having different colors and why are they named differently what's the difference between the two wires well when I first learned this I thought that one of the wires brings the electricity to our house and the other wire the black wire will take the electricity back electricity back and so this is how I should think electricity comes from say the electric poles to our house through the live wire and it goes back through the neutral wire simple right but there is a make sense mainly because we are not dealing with one directional current right you remember that we are dealing with alternating current the current which keeps changing its direction once the current flows like this then the current flows this way so it doesn't make sense to say one wire brings in electricity another wire brings out electricity because the electric current keeps on changing its direction so again what's the difference between these two wires well it turns out it's got something to do with voltage if you look at this black wire its voltage is always maintained very close to the voltage of the ground and we'll see in a second what this really means okay and that voltage is often taken to be zero and if you look at this livewire it has a very high voltage so this has high voltage and the voltage difference between these two wires in India is often around 220 volt if you're wondering why this particular number it's got something to do with history and Edison and lightbulbs and cost will not get into that okay don't worry about why this 220 it just happens to be 220 for India but again what does that even mean well that means if the current is flowing say in this direction then this wire must be having a higher voltage compared to the ground we usually call that as the positive voltage but then when the current is flowing in the opposite direction then this should have a higher voltage right but its voltage remains the same now the voltage of the wire becomes less than zero it can become negative and that's when we'll have negative voltage so the voltage of the live wire swings between positive voltage and negative voltage making the current alternate but the voltage of the neutral wire remains pretty much the same and we can imagine this to be similar to a slide one end of which is connected to the ground other end is free to move up and down so when the other end is up notice the ball goes to the right this way and now if I move this end down the ball comes back so by moving that end up and down notice above the ground below the ground I can move the ball back and forth back and forth so this end is like the live wire its voltage keeps going above the ground and below the ground back and forth making the current go back and forth on the other hand the other end is like the neutral wire it's always having the same voltage as that of the ground so make sense so what does that mean now this means that if let's say a cat comes and touches this neutral wire and let's say the insulation is broken right then what's going to happen to that cat well over here the voltage is zero let me use white oh well here the voltage is zero even at the ground the voltage is zero since the voltage of this is the same as that of the ground there is no potential difference coming across the cat and as a result there'll be no current flowing through the cat so the cat will not get a shock but what if that same cat we're to go and touch the live wire can you guess what's gonna happen the cap is gonna have a very shocking experience because now notice the live wire is either having a much positive voltage compared to the ground or much negative voltage compared to the ground compared to the neutral compared to the ground and as a result in either case this charges will flow between the wire and the earth resulting in the cat getting a nasty shock and that's why that wire is called live or hot wire saying that it's an extremely dangerous wire do not touch that wire don't worry no cats were harmed in the making of this video now of course this is not me and you go and touch the neutral wires definitely not because this is in the perfect world in reality the voltage may not be exactly equal to that of the ground so you might still get a shock there can be false and everything so it's always dangerous to you know play or touch these wires I recommend not doing that at all but in short the live wire is at a very high voltage compared to the ground but the neutral wire has voltage very close to that of the ground okay if the two wires are enough to provide electricity why do we need a third him right to answer that question let's attach something to this plug point let's attach a microwave let's say if you could look inside this wire you would see something very similar you would see two wires one cañedo to the live which is red one connected to the neutral and the current flows back and forth between these two and this is the internal circuit of that microwave which I've just shown as a resistor over here and so you are right only two wires are enough to run this microwave then why do we need a third wire that is in case of a fault imagine when this microwave was installed in your home some some handling happen and let's say the insulation of the live wire broke off and start started touching the metallic keys let's say so here's a situation let me zoom in so you can see the insulation has come off and the live wire is not touching the metallic case now again let's bring back our kitty she's gonna have a bad day today if I switch on the plug now what do you think is gonna happen well because the live wire is touching the metallic case and metal is a conductor electricity will start flowing through the metallic case through the cat and into the ground again giving our cat a very very nasty shock that is extremely bad we want to avoid that how do we do it that's where the third wire comes into place there will be a third wire which is usually green in color which is directly connected to the metallic body and it goes all the way to the plug comes out of the third pin again let's zoom out comes out of the third pin and then where does this wire go you know let me get rid of that basketball all right you know whether that goes that wire eventually comes out of your house and eventually is you know put inside the ground and so this third wire is often called no surprise ground wire this is the ground wire or the earth wire it can also be called the earth wire so how does that help well now instead of the electricity flowing through the cat that electricity will flow through this ground wire and go directly into the earth wire by will it go through the wire and not through the cat because the wire has a much smaller resistance this entire path has much smaller resistance compared to the cat and you might know already that electricity it tends to flow through the smaller resistance paths so almost all the electric current will flow through that part ensuring the safety of our kitty so in short if there is any current leaking due to any fault the ground wire ensures that we don't get electrocuted at this point you might say wait wait wait a quick thing not all the plug points have a three pin right for example mobile chargers and say my macbook charger has only two pins what's going on there well that just means that the amount of current we are dealing with over there is so minuscule that even if we get a shock it's not a big deal so it's not worth investing in putting another pin in fact my MacBook does give me a shock every time it's charging it's not a big deal all right so only we are dealing with high currents high power devices that's when the third pin becomes super important so with that let's come back to the original question why is the top pin which we now know as the ground pin why is that always longer and thicker than the other pins can you pause and think about this well if the ground pin is longer that means when you're inserting it's the ground pin that gets connected first meaning our device is made safe first and only then that these two pins get connected meaning only then the current starts running through this device to ensure that we will not get electrocuted in any case and similarly when you are removing the plug again we're ensuring that the ground is the last one to get disconnected so we first disconnect the the electricity from the from the device and then we disconnect the safety the ground wire ingenious right and of course the ground pin is also made thicker to ensure that we connect the plug in the proper position this way there is no chance that the ground pin will get inserted into the live hole which can again cause problems anyways that's it for this video so let's see if we can quickly recall the important things do you remember what are the names of these three wires then can you recall what is the voltage difference between these two wires in India with that try explaining to your friends or your family why is it dangerous more dangerous to touch the red wire compared to the black wire what's the difference between them and also how does the green wire ensure safety and with that try explaining to your friends why in the 3-pin one of the pin is always longer than the other if you have any difficulty answering any of these questions nobody's just go back and watch that part of the video