If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Overload & short circuit: Domestic circuits (Part 3)

Overload happens when current exceeds a safe value. Sometimes this happens due to voltage spikes. Attaching too many devices is also a very common cause. Sometimes there is a short circuit. A short circuit is when a very low resistance path is created, causing enormous amounts of current. For example, when a live wire touches a neutral wire, it creates a short circuit. Overload protection and short circuit protection can be done by using an electric fuse. Created by Mahesh Shenoy.

Want to join the conversation?

Video transcript

overload and short-circuit are very commonly heard falls in circuit systems so let's explore in this video what these mean so let's start with overload overload so what does this word mean well it kind of tells you that there is too much of something right over load too much of something so in electronics or in circuits the word overlord kind of means too much current too much current and why is that bad why is it bad to have too much current well let's look at a typical household circuit we have already seen that there are live wires and a neutral wire and a ground wire and everything I've talked about this in previous videos now every wire has a certain cap capacity to with the whole current a certain capacity of the current that can flow through it if the current exceeds that particular value then what happens is that the heat generated will be too much the temperature will start increasing and because of that a lot of bad things can happen like for example the insulation of these wires can start you know melting off exposing these wires and those wires can start touching otherwise it can be very bad and in the worst case it can even catch fire so too much current causes too much heat which can cause fire and that's why overload is very very bad for us so basically all there is too much current and how do we ensure that doesn't happen in our circuits well you may have once all seen about this that's the whole idea is using a fuse a fuse is basically a wire which has a high resistance and a very low melting point which ensures that it's the the wire the fuse wire starts heating up first and melts first so if the current exceeds a particular value before these wires you know start feeling the heat literally before these wires do that it's the fuse wire that will melt and immediately cut the circuit break the circuit so ensuring that all our devices are all the wires and the devices are safe all right so that's basically how overload protection pretty much works in the most basic terms and of course today we also have something called circuit breakers which is a little advanced version of the fuse you see the fuse once the wire melts you have to change the fuse wire right so it's a headache but with circuit breakers automatically it breaks the circuit as a switch it works on a similar principle but a little advanced will not talk too much about that okay so we got what we understood what overload is but the question could be what causes this overload right what what causes too much current to flow in our circuit well there could be multiple reasons for that so one of the reasons could be so let me just write that down over here one of the reasons that causes you know too much current is basically too much voltage too much voltage what does that mean well we've already seen that the the typical value thereof value of the voltage between the live wire and the neutral wire in India is about is about 220 volts right that's supposed to be the voltage and all your devices are designed to work on that voltage however sometimes you know due to certain you know certain things like you know maybe there is a lightning strike or there is suddenly a huge magnetic field comes in or some static electricity something right due to something voltage can suddenly increase we call it as a voltage spike so if a voltage increases in the circuit immediately all the current in the circuit will start increasing so that's one of the ways in which overload can happen and again fuse protects us from such voltage surges another way in which an overload can happen is you know there is no too much voltage nothing is happening when it comes to voltage but we could be using too many devices too many devices and what does that mean well we've all been there right we that one o'clock point is not enough for us so what do we do we attach an extender and then we start attaching to many devices to it now each of these device is drawing some current and therefore the total current drawn in the circuit starts increasing right the more devices you attach the more current it gets drawn and again eventually the same problem can happen if the current drawn is just too much it's more than the capacity of this then we say there's an overload happening so this time the old would happen because too many devices and that's why it's always advisable not to do this in fact in a lot of books and a lot of people will say this is what we call as overload okay to attaching too many devices many people will say that that's basically what overloading means but this is just one of the ways to overload okay OneNote is a very general term you know all right another way of having overload or of getting over load would be to create something called a short circuit short circuit again you may have heard of this word what is the word short circuit mean right in in in short okay short it kind of means you're creating a low resistance path low resistance part this usually happens when the wires start teaching each other so let me tell you what it means now in this particular circuit let's say we attach some device over here then the current starts running this way right there will be a current running from here it'll go through the device it will run through that device it'll come back from here let's say this is a normal condition normal part of the circuit but now imagine somehow the live wire and the neutral wire they lose their insulation they start touching each other let's say something like this happens okay let's say let me zoom in over here this is where they have lost insulation and the wires are touching each other now notice there is a path from the neutral - from the life to neutral over here current can flow like this and the resistance from here to here is extremely low right and so what we have now done is created a short circuit we have created an extremely low resistance part to go from here to here in such a case most of the current will now flow from here to here so you know what's gonna happen instead of current flowing this way almost all the current will now start flowing this way and now why that is bad is because if the resistance is very low and you have a pretty high voltage of Rojo 220 volts that means the current in this is super high it can be in terms of thousands of amperes so the current is going to be pretty strong and again we're gonna overload our circuit too much current is overloading again it's the fuse that helps us protect against that and of course this short circuit can happen anywhere like for example imagine you attach some device over here okay you've had some device over here and let's say you know we have two wires coming in you actually have three wires coming in there's also a grounding wire but I'm ignoring the grounding wire but again the same the same fault happens inside this inside this particular wire let's say the two wires are touching each other then again there is a short crit let me get rid of this short circuit okay let me get rid of this short circuit so now a short circuit is created over here now again the current instead of flowing all the way through the device they couldn't we just flow from here to here right again a short circuit and again that's bad because you know too much current too much heat it can damage this device all right are there other ways of creating short circuit yes you may know water can cause short circuits so what's happening over there the idea is imagine you have some circuit and again let's say this is the normal part that the this is the normal path that the current should take from here to here let's say now if there is a lot of water and the water has salts then that water is conducting so now there is a path available from here to here there's a path available from here to here for example see and these are all extremely low resistance paths that means a very high current can start flowing from here to here right that's an abnormal as an abnormal current and so again that's bad because I can heat things up and if these there are microchips over here those microchips can easily melt and they can stop working and that's why when you throw your phone inside water if the phone is switched on if the current is running it's pretty much a goner mainly because the water creates a short-circuit so that's pretty much it let's quickly recall what we just learned so can you recall what is the meaning of overload in electrical circuits and why is it bad then how does overload happen what are the different ways in which overloading can happen can you explain what a short-circuit is now what is the meaning of the word short-circuit can you explain that to say a friend and finally can you explain what protects our circuits from these files of overloads and short circuits do try answering these questions and if you have some difficulty go back feel free to go back and watch the video again