Short circuit protection relay circuit fail

I saw at Facebook a video 12 v Short Circuit Protection and same for 220 volts ( It was advertised as a short circuit protection relay circuit that will turn off the power when output is short circuited.

This seems to be a quite popular circuit idea, because I saw several very similar circuit designs on YouTube:

When presented on the videos those are claimed to be a nice protection circuit, and the circuit design might work on same cases (but not all).I would rather rely on proper circuit breaker or fuse because it will protect against short circuit and overload.

This approach shown in video is far from foolproof. If you for example put the circuit next to battery and have long thin wires to motor, this circuit does not react to short circuit at all! The example circuit works on the principle that if the output is short-circuited, the voltage over relay coil drops and the relay releases. The circuit works only of the input voltage drops enough due the short circuit (drops to 2/3 or half of original voltage with typical relays) and does not work if the input voltage does not drop due short circuit on output (for example protection circuit next to var battery and long thin wires to the load being sensed).

This circuit can have it’s uses, but in addition to it you should have fuse/breaker or for sure current limited power supply.

Warning: At 220V you can expect exploding relays with mains circuits that have high short circuit current (hundreds of amperes to kiloamperes)!

Here is Short circuit relay protection not working video by Riton Lafrizoute showing how this circuit fails:


  1. Varun Sharma says:

    Nice article. Keep it up.

  2. Nisha Batel says:

    Nice and wonderful blog, great work.

  3. Tomi Engdahl says:

    it works somewhat on some usage situation and fails to work on many cases. This is not reliable protection.
    This circuit trips only if short circuit causes the voltage on circuit power input to drop enough by short circuit. If you have power supply where voltage does not drop with even high load, this circuit will not trip at all. For example when circuit is wired with short thick wires to car battery, the short circuit on output will most probably melt the thinner wires there and/or the relay on circuit will melt.

  4. Tomi Engdahl says:

    ONE FATAL FLAW: the “no power” LED (RED) and relay coil will KILL A ** BATTERY ** in Very Short Order. Therefore, it’s best used with a “wall wart” or similar AC-powered DC power supply.


Leave a Comment

Your email address will not be published. Required fields are marked *