Two safety devices protect you from a shock. With earthing, the metal casing of an appliance is connected to the earth through the green-and-yellow wire, so leaking current flows away there, not through you. The residual current device compares the current going out and coming back and switches off above a 30 milliamp difference. The fuse only protects the wire.
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The plug of your washing machine has two metal strips on its sides, the plug of your phone charger does not. Those strips are the earthing. Together with the residual current device it protects you from an electric shock; the fuse only protects the wire.
With earthing, the metal casing of an appliance is connected to the earth through the green-and-yellow earth wire. If the live wire inside accidentally touches that casing, the current flows away through the earth wire and not through you.
The residual current device compares the current going out through the live wire with the current coming back through the neutral wire. They should be equal. If the difference is more than 30 milliamps, current is leaking away, perhaps through someone, and then it switches off. A 16 amp fuse does not even notice such a small current.
Halfway through it is your turn: a washing machine with a loose earth wire, and you put your hand on the casing. Which protection switches off? At the end there are two more questions, with 40 milliamps through someone and a toaster where 3.60 amps go out and 3.55 amps come back. Pause the video at each question and think it through first.
In this video
The full explanation, in writing
Two metal strips
0:00The plug of your washing machine has two metal strips on the side. Your phone charger's plug does not. What are those strips for?
Earthing and the residual current device
0:14The fuse protects the wire. There are two more safety devices, and they are there for you, not for the wire. Earthing: the metal casing of an appliance is connected to the earth through the green-and-yellow wire. If the live wire inside accidentally touches that casing, the current flows away through the earth wire and not through you.
0:36And the residual current device compares the current that goes out through the live wire with the current that comes back through the neutral wire. Those should be equal. If the difference is more than thirty milliamps, current is leaking away, maybe through someone, and then it switches off.
0:56Your turn. In a washing machine the earth wire is loose, and inside, the live wire touches the metal casing. You put your hand on it. Which safety device switches off?
Which protection switches off?
1:12The earth wire is loose, so the current cannot flow away through the earth and goes through you to the ground. Then less comes back through the neutral wire than went out through the live wire. If that difference is more than thirty milliamps, the residual current device switches off.
1:30The fuse notices nothing: such a small current is nothing to it.
Three things to remember
1:35Three things. The fuse protects the wire, not you. Earthing: if the live wire touches the metal casing, the current flows through the green-and-yellow wire to the earth, and not through you. And the residual current device compares out and back: if the difference is more than thirty milliamps, the power goes off.
Two questions
1:58Two questions. One. Forty milliamps flows through someone to the ground. Does the fuse switch off, the residual current device, or both? Two. Through the live wire of a toaster three point six zero amps goes out, and through the neutral wire three point five five amps comes back.
2:16Does the residual current device switch off?
The answers
2:22The first: only the residual current device. Forty milliamps is nothing to a sixteen-amp fuse, but it is more than thirty milliamps of difference between out and back. The second: three point six zero minus three point five five is zero point zero five amps, and that is fifty milliamps.
2:42More than thirty, so it switches off.
Fuses
2:46Want to know why the fuse blows when you switch on too much at once? Then watch the video on fuses on my YouTube channel.
Frequently asked questions
What does earthing do?
With earthing, the metal casing of an appliance is connected to the earth through the green-and-yellow earth wire. If the live wire inside accidentally touches that casing, the current flows away through the earth wire and not through you. You recognise it by the two metal strips on the sides of the plug.
How does a residual current device work?
A residual current device compares the current going out through the live wire with the current coming back through the neutral wire. They should be equal. If the difference is more than 30 milliamps, current is leaking away, perhaps through someone, and then it switches off.
Does a fuse protect you from an electric shock?
No. A fuse protects the wire, not you. A current of 40 milliamps through someone is nothing to a 16 amp fuse, so it stays intact. Earthing and the residual current device are what protect you from a shock.
What happens if the earth wire is loose and you touch an appliance?
If the live wire then touches the metal casing, the current cannot flow away through the earth and goes through you to the ground. Less then comes back through the neutral wire than went out through the live wire. If that difference is more than 30 milliamps, the residual current device switches off.
Does the residual current device switch off if 3.60 amps go out and 3.55 amps come back?
Yes. The difference is 3.60 minus 3.55, which is 0.05 amps, and that is 50 milliamps. That is more than 30 milliamps, so the residual current device switches off.
Next: why the fuse blows when you switch on too much at once. That is in the video about fuses on this channel.
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Physics with Thomas: explained with pictures where they add something, and without them where they distract.
In this series
Electric currentthe electrons crawl, your lamp is on at once6:12
Voltage and capacitytwo batteries, the same number4:43
Connecting ammeter and voltmeterswapping them wrecks your meter4:10
Direct and alternating voltage and the diodewhy does an LED only work one way?4:11
Resistance and Ohm's lawdoes resistance double with voltage?4:21
Resistance of a wirewhy a long cable charges slowly4:40
Variable resistor, NTC, PTC and LDRresistors that change by themselves3:40
Series circuitwhich lamp gets the most current?3:32
Parallel circuitwhy does the resistance actually get smaller?3:56
Series-parallel circuitwhy adding up doesn't work here3:37
Circuits practical testhow to find the resistor under the tape5:13
Powerwhy is there no such thing as watts per hour?2:58
Kilowatt-hourwhat does your wifi router cost per year?3:05
Efficiencywhere does the rest of the energy go?3:43
Earthing and residual current devicewhat protects you from a shock?2:58
About me
My name is Thomas Schuurmans, and I have a passion for physics and for understanding why things work the way they do. What I want is to get young people asking “why is that?” and “how does that work?” more often, and to hand them the tools of physics in a way that is simple and that you can see.
I graduated in applied physics at Delft University of Technology in 2003. After that I spent more than twenty years outside education: first at TNO, the Dutch applied research institute, then at a design agency, and eventually founding Proportion Global, through which I work on innovation questions in Africa, Latin America and South Asia. That work resembles physics more than you would expect: don't start from a solution, first understand what is going on, try something, be wrong, and look again.
Proportion Global now works with a network of local consultants in 67 countries, so I hardly need to travel myself any more. That gives me more time, and more of a need, to make a difference closer to home as well. So I picked up my old love for physics again. Since September 2026 I have been teaching physics two mornings a week at the Cartesius Lyceum in Amsterdam, to lower and upper secondary classes.
I am very much a visual learner myself when I want to learn something new. That is where the idea came from: videos that explain one topic sharply and visually, in just a few minutes. I make them for my own pupils. Then I publish them, because a good explanation should be within reach of anyone who needs it, wherever you live and whatever language you think and speak in.