I want to protect from short circuit by using a miniature circuit breaker. But this has to be manually turn ON, when ever it is turned OFF. So I was thinking to make a electronic circuit breaker which cuts the power supply when ever there is a short circuit. And able to read the state of the circuit and turn it back ON using a micro controller. I am using 230V AC. And a Max Current of 16A.

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    \$\begingroup\$ OK, but what is your question? Where are you stuck in your design? Have you figured out how the microcontroller will know that the short has been removed? (You can't unless you feed some current.) Why not just use a voltage regulator with a current limit setting or add a polyfuse inline with the output? \$\endgroup\$ – Transistor Jan 21 at 7:20
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    \$\begingroup\$ I can design circuits that are short circuit proof yet do not need a "miniature circuit breaker". You should explain in more detail what your circuit is and what you want to protect against. Don't go into a solution (example: I need to use a circuit breaker) because there might be a smarter way to solve the issue or your issue might not be an issue at all. Also: a circuit breaker might be too slow, a component might have been damaged before the circuit breaker breaks the circuit. \$\endgroup\$ – Bimpelrekkie Jan 21 at 7:25
  • \$\begingroup\$ I want to protect individual sockets from short circuit, to protect the devices connected to the same power extension board. And I should able to monitor the state of the sockets(weather they are short circuited or not). So that it would not affect other devices connected in the extension board. \$\endgroup\$ – Hari Jan 21 at 7:38
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    \$\begingroup\$ "I am using AC." 6 V AC? 120 V AC? 230 V AC? What is the maximum instantaneous short circuit current that your mains system could provide? What are you going to use to interrupt this very high current? What is the required response time? \$\endgroup\$ – Transistor Jan 21 at 11:58

Something like this should work:


simulate this circuit – Schematic created using CircuitLab

The shunt resistor is 1 ohm, 1 A will cause 1 V voltage drop. set the maximum current allowed via non-inverting pin of the op amp. If voltage drop on the shunt is bigger than the reference voltage, op amp will drag it's output to negative rail and vice versa.

we configured the op amp as comparator, so the output is either high or low. connect the output of the op amp using a resistor to the digitalRead of MCU. in the program if the current is higher than what you set (digitalRead == LOW;), energize the relay and "break the circuit". you should put some delay in there too, otherwise it will keep connecting and disconnecting the relay. or you can manually connect the relay in case short circuit happened.

It's literally just four components, using miniature relays and SMD op amp/resistors it shouldn't be bigger than 4-5 centimeter.


For AC current sensing you can use the same circuit except instead of using a shunt resistor to sense the current. Use an hall effect sensor and feed it's output to the op amp inverting pin:

ACS712 datasheet

  • \$\begingroup\$ Thanks for your answer. But I am really sorry as I forgot to mention its for AC. \$\endgroup\$ – Hari Jan 21 at 8:50
  • \$\begingroup\$ @Hari See the edit. \$\endgroup\$ – ElectronSurf Jan 21 at 9:59
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    \$\begingroup\$ Note that this will switch off the current after some time delay and your circuit breaker should have tripped before that. Also note that, while you have accepted the answer, it doesn't address your requirement that it be able to sense removal of the short circuit for automatic switch on. It doesn't seem like a good idea. The ACS712 is unlikely to be rated for the fault current, may be damaged by it and the isolation between it and your proposed controller may break down and make the controller circuit live. Circuit protection is a very complex subject. \$\endgroup\$ – Transistor Jan 21 at 12:01
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    \$\begingroup\$ I don't think there is a solution other than to use an inverter design which can electronically limit the current to a safe value. A short circuit on a mains supply can cause hundreds of amps to flow. This is likely to destroy whatever switch the OP could come up with. It's also not clear why s/he's expecting short-circuits on the sockets in the first place. I'd prevent that instead. \$\endgroup\$ – Transistor Jan 21 at 13:23
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    \$\begingroup\$ @Hari: Use a more sensitive and faster acting MCB at the workbench. If you're testing a device that should only draw 1 A then use a 3 A MCB. European MCBs are have A, B, C and D ratings which indicate their response times with A being the fastest. That means you will have a local reset without having to go to the fuseboard. You do not want the reset being done by microcontroller. \$\endgroup\$ – Transistor Jan 22 at 9:13

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