• Skip to main content
  • Skip to primary sidebar

Homemade Circuit Projects

Get free circuit help 24/7

New Projects | Privacy Policy | About us | Contact | Disclaimer | Copyright | Videos | Circuits for Beginners | Basic Circuits | Hobby Projects | Transistor Circuits | LED Drivers 

You are here: Home / Home Electrical Circuits / Mains AC Short Circuit Breaker/Protector – Electronic MCB

Mains AC Short Circuit Breaker/Protector – Electronic MCB

Last Updated on September 14, 2020 by Swagatam 91 Comments

caution electricity can be dangerous

In this post we will try to understand the making of a simple 220 V, 120 V AC mains short circuit breaker using an SCR and a triac combination, (researched and designed by me).

The circuit is an electronic version of the normal main circuit breaker MCB units that we use in our homes.

Note: I did not use a relay for the cut-off, because relay contacts will simply fuse with each other due to heavy current arcing across the contacts during a short circuit condition, and therefore it is highly unreliable.

Why Short Circuit in Homes Can be Hazardous

A short circuit in a house wiring may appear to be something which happens very seldom and folks aren’t too interested to get any relevant precautionary measure installed in their houses and take the hazard very casually.

However once in a while due to some accidental fault, a short circuit in the mains wiring becomes inevitable and it the happening causes a disaster and huge lose.

At times the consequence leads to fire hazards and even lose of life and property.

WARNING - THE PROPOSED CIRCUIT IS NOT ISOLATED FROM MAINS AC, THEREFORE IS EXTREMELY DANGEROUS TO TOUCH IN UNCOVERED POSITION AND WHEN POWERED.

Though many types of short circuit breaker units are available ready made in the market, these are generally very costly.

Moreover an electronic hobbyist will always want to make such an equipment all by him and enjoy its display in the house.

Making a Cheap yet Promising Electronic Circuit Breaker Unit

A short circuit breaker circuit described in this article is indeed a piece cake as far making it is concerned and once installed will provide a life long protection against all short circuit like conditions that might accidentally take place.

The circuit will also safeguard you house wiring against a possible overload conditions.

Electronic Mains AC Short Circuit Breaker/Protector

 

How it Works

The circuit shown in the schematic looks pretty straightforward and may be verbally simulated as follows:

The sensing stage of the circuit in fact becomes the heart of the whole system and consists of an opto-coupler OP1.

As we all know, an opto-coupler internally consists of an LED and a switching transistor arrangement, the transistor is switched ON in response to the illumination of the built-in LED.

Thus the triggering of the transistor which forms the output of the device takes place without any physical or electrical contact rather through the passage of light rays from the LED.

The LED which becomes the input of the device may be switched through some external agent or a voltage source which required to be kept aloof from the output stage of the opto-coupler.

Why an Optocoupler is Used

In our circuit, the opto coupler LED is powered through a bridge network which obtains it voltage source from the potential generated across resistor R1.

This resistor R1 is connected in such a way that the AC mains current to the house wiring passes through it and therefore any over-load or over-current is subjected over this resistor.

During an over load or short circuit conditions, the resistor instantly develops a potential across it, which is rectified and sent to the opto coupler LED.

The opto LED immediately illuminates, switching ON the corresponding transistor.

Using an SCR for triggering the main Triac Cut out Stage

Referring the circuit we see that the opto transistor’s emitter is connected to the gate of an external SCR, whose anode is further connected to a Triac's gate.

During normal conditions, the triac remains switched ON, allowing the load connected across it to remain operational.

This happens because the SCR remains switched OFF and allows the triac to acquire its gate current through R3.

However in case of an over load or a short circuit, as discussed earlier, the opto-coupler transistor conducts and triggers the SCR.

This instantly pulls the gate potential of the triac to ground, inhibiting it from conducting.

The triac immediately switches OFF, safeguarding the load and the house wiring to which it is configured.

The SCR remains latched, until the problem is rectified and the circuit is restarted.The section comprising C1, Z1, C2 is a simple transformerless power supply circuit, used for powering the SCR and Triac circuit.

Parts List

  • R1 = iron coiled wire; its resistance is calculated to produce 2 volts across it at the determined critical load conditions.
  • R2, R3, R4 =100 Ohms
  • R5 = 1K,
  • R6 = 1M,
  • C1, C2 = 474/400V
  • SCR = C106,
  • Triac = BTA41/600B
  • Opto-Coupler = MCT2E,
  • ZENER = 12V 5W
  • Diodes = 1N4007

You'll also like:

  • 1.  Climate Dependent Automatic Fan Speed Controller Circuit
  • 2.  Cell Phone Emergency Charger Pack using Ni-Cd Batteries
  • 3.  20 Watt Fluorescent Tube Circuit with 12V Battery Operation
  • 4.  Push-Button Light Dimmer Circuit
  • 5.  Closed Loop AC Motor Speed Controller using Back EMF
  • 6.  Emergency Incubator Heater Circuit with Battery Charger

About Swagatam

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials.
If you have any circuit related query, you may interact through comments, I'll be most happy to help!

Have Questions? Please Comment below to Solve your Queries! Comments must be Related to the above Topic!!

Subscribe
Notify of
91 Comments
Newest
Oldest
Inline Feedbacks
View all comments

Primary Sidebar

Calculators

  • 3-Phase Power (15)
  • 324 IC Circuits (19)
  • 4017 IC Circuits (52)
  • 4060 IC Circuits (25)
  • 555 IC Circuits (98)
  • 741 IC Circuits (19)
  • Arduino Engineering Projects (83)
  • Audio and Amplifier Projects (114)
  • Battery Chargers (82)
  • Car and Motorcycle (94)
  • Datasheets (46)
  • Decorative Lighting (Diwali, Christmas) (33)
  • Electronic Components (100)
  • Electronic Devices and Circuit Theory (36)
  • Electronics Tutorial (116)
  • Fish Aquarium (5)
  • Free Energy (34)
  • Fun Projects (13)
  • GSM Projects (9)
  • Health Related (20)
  • Heater Controllers (29)
  • Home Electrical Circuits (102)
  • How to Articles (20)
  • Incubator Related (6)
  • Industrial Electronics (28)
  • Infrared (IR) (40)
  • Inverter Circuits (98)
  • Laser Projects (12)
  • LED and Light Effect (93)
  • LM317/LM338 (21)
  • LM3915 IC (25)
  • Meters and Testers (65)
  • Mini Projects (148)
  • Motor Controller (67)
  • MPPT (7)
  • Oscillator Circuits (26)
  • PIR (Passive Infrared) (8)
  • Power Electronics (34)
  • Power Supply Circuits (77)
  • Radio Circuits (10)
  • Remote Control (48)
  • Security and Alarm (61)
  • Sensors and Detectors (120)
  • SG3525 IC (5)
  • Simple Circuits (75)
  • SMPS (29)
  • Solar Controllers (60)
  • Timer and Delay Relay (53)
  • TL494 IC (5)
  • Transformerless Power Supply (8)
  • Transmitter Circuits (40)
  • Ultrasonic Projects (16)
  • Water Level Controller (45)

Calculators

  • AWG to Millimeter Converter
  • Battery Back up Time Calculator
  • Capacitance Reactance Calculator
  • IC 555 Astable Calculator
  • IC 555 Monostable Calculator
  • Inductance Calculator
  • LC Resonance Calculator
  • LM317, LM338, LM396 Calculator
  • Ohm’s Law Calculator
  • Phase Angle Phase Shift Calculator
  • Power Factor (PF) Calculator
  • Reactance Calculator
  • Small Signal Transistor(BJT) and Diode Quick Datasheet
  • Transistor Astable Calculator
  • Transistor base Resistor Calculator
  • Voltage Divider Calculator
  • Wire Current Calculator
  • Zener Diode Calculator

© 2023 · Swagatam Innovations

wpDiscuz