Molded case circuit breakers (MCCBs) are becoming far more sophisticated, and while protecting circuits and systems they also add functionality. Switch technology is central to much of this enhancement, allowing communication with the system as well as programming of critical performance parameters. Michael Bolduc, global segment manager, industrial and consumer, C&K Switches, comments


CCBs are electrical protection devices that can be thought of as the ‘big

brother’ of the miniature circuit breakers (MCBs) that are typically found in homes or offices. They are commonly used when the load currents exceed the capabilities of MCBs, or where the application requires adjustable trip settings. MCCBs tend to be significantly larger than MCBs, and can handle currents as high as thousands of Amperes, although versions are available with trip levels of just a few tens of Amperes. In common with all types of thermal-

magnetic circuit breakers, there are two primary MCCB protection modes: • Overload protection is achieved through the use of a bi-metallic strip. • Fault protection is an electromagnetic function with an instantaneous response, as fault currents need to be interrupted immediately. MCCBs also include a disconnection

switch that can trip the breaker manually. This is used to disconnect equipment from the power supply during maintenance or system upgrades. Recent developments, however, have seen MCCBs becoming more ‘connected,’ allowing remote control

and monitoring of parameters such as phase current and voltage.

SWITCHES FOR MCCBS There are two primary roles for switches within MCCBs. They are typically used for setting the main parameters, such as the trip current and time delays, and also as auxiliary switches to execute various functions once the MCCB has been tripped. Two very different types of switch are required here. For setting the trip current a form of PCB-mount DIP switch is often used. These switches can be either a rotary design (most common) or occasionally standard in line piano style DIP switches. While reliability is less of a concern due to infrequent use, ensuring that the current is set correctly is vital for safety and avoidance of nuisance trips. The auxiliary switch is generally a type of

micro switch which is used for notification as well as to control external devices in the event of a trip condition. While usage

may not be high compared to other applications, the need to control various devices can be a challenge for designers. Control of warning lights, relays and external power supplies may require currents in the 10-15A range. One of the primary requirements for the auxiliary switch is mechanical compatibility with the MCCB so that it can be easily and quickly removed if the end customer wishes to re-configure various functionality. This usually involves customisation of a standard micro switch to add an overmolded housing with quick-release latches.


The wide RTE range of mechanical options provides simple mounting in compact spaces

APPLICATIONS The two primary types of switch used in MCCBs are: RTE series – low-profile rotary DIP switch: Flexible and versatile, this is

The TM snap-acting series is commonly customised for use in MCCB applications

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