Miniature Circuit Breakers, Circuit Breakers

Miniature Circuit Breakers: Learn About Miniature Circuit Breakers Here > A miniature circuit breaker is a device that switches and/or protects the lowest common distributed voltage in an electrical system. It is designed to protect conductors and insulation from damage due to overload short circuit.


Miniature Circuit Breaker Uses
Components of a Miniature Circuit Breaker

Miniature Circuit Breakers fall in to two categories. These categories include: Residential and Industrial.

• Residential Miniature Circuit Breakers - Residential miniature circuit breakers are only of the plug-in type. These are designed for residential loadcenters, commercial units, and light industrial applications. They typically range from 10 to 125 amps, with an interrupting rating of 10 or 22 KAIC.
• Industrial Miniature Circuit Breakers - Industrial breakers are designed for three types of mounting applications: plug-in, bolt-on, and cable-in/cable-out. Industrial miniature circuit breakers are designed to protect small branch circuits in commercial or industrial electrical distribution systems. They are applied in loadcenters, lighting panelboards or individual mounting applications. They typically range from 6 to 125 amps, with an interrupting ratings as high as 65 KAIC.

Miniature circuit breakers have a simple construction, although, the parts that make up a miniature circuit breaker work in a very precise manner. The miniature circuit breaker does not offer replacement parts. It's not designed to be maintained, rather, when a unit goes bad, it is simply replaced.

A typical miniature circuit breaker is made up of four main components: the Frame, the Operating Mechanism, the Trip Unit and the Contacts.

1. Frame - The miniature circuit breaker frame has a molded case exterior. Its primary function is to provide a rigid, mechanically strong, insulated housing in which the other components are mounted.
2. Operating Mechanism - The operating mechanism of a miniature circuit breaker provides the means of opening and closing the circuit. It has a three-position switch ("on", "off", and "tripped"). It can only be in the "tripped" position as a result of an overcurrent. When power is removed manually, it can only be switched to the "off" position. This makes it easy for a maintenance person to determine why power has been cut.
3. Trip Unit - The trip unit of a miniature circuit breaker acts as the brain of the device. It activates the operating mechanism in the event of a prolonged overload or short circuit. This type of circuit breaker uses a thermal magnetic mechanism. This is the predominant trip unit technology used in the domestic market. A bimetal and an electromagnet work together to provide overload and short-circuit protection.
4. Contacts - When an overload or short circuit situation occurs, the miniature circuit breaker contacts open to break the current flow. When this happens, an electrical arc is formed. The arc continues until the first possible zero point in the AC cycle. The zero point is the weakest point in the AC cycle and will not support the continuance of an arc. By breaking the arc, current flow is stopped. This is called zero point construction.

The Miniature Circuit Breaker cutaway above diagrams the different components of the miniature circuit breaker, including the trip lever and the operating mechanism.

There are many other features to consider when choosing a miniature circuit breaker for any application. Some of the important features to pay attention to when choosing a miniature circuit breaker are Circuit Breaker Ratings, Number of Poles of the miniature circuit breaker and the different mounting methods for the specific type of miniature circuit breaker in use.