What is MCB (Miniature Circuit Breaker)? How Household MCB Works?

Definitely, you have noticed switch looking gadget in modern household which automatically becomes off upon fault in line. They are called MCB – Miniature Circuit Breaker. Why These Days We Are Seeing More Usage of MCB in Household than Before? It is Common to Ask – What is MCB (Miniature Circuit Breaker)? How Household MCB Works? In this guide, we hope that we will be able to answer the common questions. In our previously published articles, we discussed about common types of fuses which are used in household. In older article, we also discussed around common types of switches. Circuit Breakers are electromechanical devices which has an internal switch mechanism which is triggered by an unsafe surge of electricity.

What is MCB (Miniature Circuit Breaker)?

Circuit Breakers or miniature circuit breaker or MCB or colloquially breaker is a overcurrent protection device which is type of a switch. Miniature circuit breakers are for low voltage lines (less than 1,000 volt) to protect the lines from damage due to overheating due to excessive current. The circuit breaker is a reusable, not automatically resetting fuse element. Early form of circuit breaker was described by Thomas Edison in 1879, but generally accepted that modern form was invented in 1924.

A combination of a miniature circuit breaker (MCB) with a residual-current device (RCCB) is used as RCBO (Residual current operated Circuit Breaker with Overcurrent protection).

How Household MCB Works?

Actually, there are various types of miniature circuit breakers (MCB). However, the common type follows quite simple principal of operation. One unit has two contacts. Among which one is fixed and the other is not fixed, can move. There is a solenoid at the end which can move. When the current exceeds the threshold limit, the solenoid forces the contact to mechanically get disconnected from the fixed part. For over heating, a simple a bi-metallic strip can be used. MCBs better at detecting over current fault – generally within 2.5 millisecond it shuts down the system. For overheating, it may take up to 2 minutes to work.

When a high current (or voltage) is interrupted, an arc is generated. Arc has a length. The length of the arc is proportional to the voltage, intensity is proportional to the current, heat is proportional to the current. Obviously that arc is controlled in different ways so that the gap between the contacts again withstand the load in the circuit. Different circuit breakers use vacuum, air, insulating gas, oil for handling that arc.

We can have single pole MCB (for LINE/PHASE), double pole MCB (includes neutral too) and Residual Current Circuit Breaker (discussed later).

Understand the Basic, Measure and Help Your Electrician to Plan

Commonly, we are used with Rewirable Ceramic Fuse. Such fuse is a piece of metal wire which melts when overheated an needs replacement. Miniature Circuit Breakers are convenient as secondary “fuse” at distribution box adding more advantages. Fuses quicker to interrupt the circuit, but needs replacement and usually handles overheating poorly, sometimes can not. MCB are not exactly replacement of traditional fuses. Rather, if they are in circuit before a Rewirable Ceramic Fuse or Cartridge Fuse, it is highly likely that the Fuse will not be blown away avoiding hassle. Both, MCB and any Fuse needs checking of the fault in circuit (or line) before reactivating them.

Combining Rewirable Ceramic Fuse and MCB (Miniature Circuit Breaker) together in a line where high wattage devices will be used (like air-conditioner, refrigerator, microwave oven) we have near 100% coverage of overheating and overcurrent situations. These days, with increasing electronic devices, it is practical to add MCB for each room. Essentially combining Rewirable Ceramic Fuse and MCB (Miniature Circuit Breaker) together in a line will protect the wiring to get melted (wire is more costly) to make the faulty device unusable.

We suggest to measure the highest possible load in each room as unit for each MCB, calculated by using multimeter by you to help your electrician wiring efficiently. Of course, we can use a clamp multimeter to measure load of our household appliances.

Trip current of some MCB may be adjusted offering dynamic advantage. There is Earth Leakage Circuit Breaker to protect the circuit from the electrical leakage.

MCB Can Make DIY Electronics Work Safer

If you work with DIY electronics stuffs and use AC to convert to DC, ideally you should have additional MCB for that plug limiting current (more than 5A not necessary, whereas your air-conditioner may need 16A to 20A MCB). You can actually use a MCB as mechanical switch but that is not what most manufacturers suggest. Main switch of your household usually have limit to 32A.

There are different safety devices and combining them is practical.

Earth Leakage Circuit Breaker (ELCB) is used to protect the circuit from the electrical leakage when someone gets an electric shock within 0.1 secs. Residual Current Circuit Breaker is a current sensing equipment which can guard a human from the electrical shocks. This type of circuit breaker is perfect for the plug which will be used for DIY electronics stuffs to use AC to convert to DC or use relay for testing, developing AC things. Indeed, you should have Residual Current Circuit Breaker for using your developed circuit to control AC stuffs in other rooms. There are Portable Residual Current Devices, like plugs.

It is practical to invest some money for higher protection.