【Product knowledge】What is MCB and RCB
MCB and RCB circuit breakers are widely used as products for household and similar purposes.
What is MCB and RCB?
MCB is a miniature circuit breaker, while RCB is a circuit breaker with residual current protection. Different loads should choose different types of circuit breakers.
What is a Miniature Circuit Breaker (MCB)?
MCB or Miniature Circuit Breaker is an electromagnetic device that embodies a complete housing in molded insulating material. The main function of the MCB is to switch the circuit, i.e. to automatically open the circuit (which has been connected to it) when the current passing through it (MCB) exceeds the value set by it. It can be turned on and off manually like a normal switch if desired.
Construction of MCB
MCB embodies a complete housing in molded insulation. This provides a mechanically robust and thermally insulated enclosure. The switching system consists of fixed and moving contactors, which are connected together to the output lines. Metal or current-carrying parts are made of electrolytic copper or silver alloys, depending on the rating of the circuit breaker.
An arc is formed when the contacts separate under overload or short circuit conditions. All modern MCBS is designed to handle the arc interruption process, with arc energy extraction and cooling provided by metal arc splitter plates. These boards are held in place with insulating material. Additionally, arc runners are provided to force an arc between the main contacts.
The operating mechanism consists of magnetic tripping and thermal tripping devices.
This magnetic trip unit basically consists of a composite magnetic system with a spring-loaded snubber with a magnetic plunger in silicon fluid and a normal magnetic trip. A current-carrying coil in the trip unit moves the shrapnel relative to the spring to the fixed pole piece. Thus, when the coil generates a sufficient magnetic field, a magnetic pull is created on the pulling liver. In the event of a short circuit or heavy overload, the magnetic field generated by the coil (solenoid) is strong enough to attract the armature that trips the liver, regardless of the position of the slug in the buffer.
The thermal trip unit is surrounded by a bimetallic band around which the heater coil is wound, thereby generating heat according to the flow of electric current. Heater designs can be direct, where current is passed through a bimetallic strip, which affects part of an electrical circuit, or indirectly, with a coil of current-carrying conductor wrapped around a bimetallic strip. The deflection of the bimetallic plate activates the trip mechanism in certain overload conditions.
Bimetallic bars consist of two different metals, usually brass and steel. These metals are riveted and welded along their length. These are designed so they don't heat the strip to the trip point for normal current, but if the current exceeds the rated value, the strip gets heated, bends, and trips. The bimetallic strip is chosen to provide a specific time delay at a specific overload.
Things to be careful about when purchasing and using MCB and RCB
1. Choose branded products sold through formal channels and products with CCC certification marks.
2. Select the appropriate technical parameters according to the application occasion. Such as rated voltage, rated current, number of poles, rated residual operating current, etc.
3. It shall be installed and maintained by professionals according to the provisions of the manual; if serious damage such as a short circuit occurs during use, it shall be replaced in time.
4. Pay attention to keeping the place of use dry and clean to maintain the insulation strength of electrical products and prolong the service life.
