Engineering Tutorials

Miniature Circuit Breakers

As previously stated, 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 (or Overcurrent) and Short Circuit.
For most people, the easiest way to visualize this application picture is to think in terms of a loadcenter in a home (Figure 3). The circuit breakers inside the loadcenter are miniature circuit breakers.
Think about the electrical utility and where the electricity is generated. The residential loadcenter is certainly at the end of the distribution system. It is here that the voltages are the lowest of the distributed voltages in the electric utility's system.

End of the Line Distribution System (Loadcenter)

Miniature circuit breakers are not just for residential applications only. They are used in residential, commercial and industrial applications.
In an industrial or commercial application, miniature circuit breakers can be found in loadcenters, lighting Panelboards and individual mountings.
Applications
Miniature circuit breakers fall into two categories. These are:
• Residential-Residential miniature 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-These breakers are designed for three types of mounting applications: plug-in, Bolt-On, and Cable-In/Cable-Out. (We will look at mounting methods shortly.)
Industrial miniature 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.
Some potential customers are original equipment manufacturers (OEMs) involved in industrial control panels and electrical machinery, such as machine tool equipment, material handling and packaging systems. In addition, look for involvement with printing machines, food-processing systems, uninterruptable power supplies (UPS) and HVAC (heating, ventilation and air conditioning).
Pictured here is a typical residential loadcenter. Each miniature circuit breaker in the loadcenter protects a branch circuit. Two branch circuits are shown, each providing power to common residential loads.



Each miniature breaker is rated to handle a specific load. For example, a circuit breaker protecting a branch used with kitchen appliances has a higher rating than a circuit breaker protecting a branch with an overhead lighting fixture on it.