How to Choose the circuit breakers types?

Determining the right circuit protection device for a specific application is not difficult, but it does require some thought. If electrical and electronic equipment is designed with circuit protection devices that are too loosely specified, the equipment will be easily damaged by power surges and cause catastrophic consequences such as fire. On the contrary, if circuit protection devices with too tight specifications are used, it will cause annoying frequent tripping. The current circuit breakers mainly include thermal circuit breakers, magnetic circuit breakers and earth leakage circuit breakers. When selecting a circuit breaker, the designer needs to consider not only the following circuit characteristics but also the restrictions on the installation location and housing size of the circuit breaker:

● Applied rated AC or DC voltage

● Single phase, multi-phase and number of poles

● Applicable national electrical standards and safety management agency standards

● Short circuit breaking capacity

Thermal circuit breakers

Thermal circuit breakers use a bimetallic strip connected in series with the circuit. The heat generated by the current during overload will deform the bimetallic strip, causing the circuit breaker to trip. Thermal protectors have the distinct advantage of being able to reset after tripping, compared to fuses. They can also be used as power on/off switches for the equipment being protected.

Thermal circuit breakers trip faster with increasing temperature and often at lower current levels. This characteristic is often useful when the circuit breaker and the system are exposed to the same heat source.

In this case, the protection circuit can track the equipment's need for increased wiring protection at higher temperatures. If a thermal circuit breaker is mounted in an environment separate from the equipment being protected, the effects of varying ambient temperatures can be corrected by a compensating thermal bimetallic strip. For example, a circuit breaker located outside an aircraft cabin is temperature compensated so that its tripping characteristics do not change with temperature fluctuations common in flight.

In addition, thermal circuit breakers are extremely insensitive to shock and vibration due to their inherent latching mechanism. Some high-performance circuit protection devices now offer circuit breakers specifically designed for shock and vibration environments.

Applications that require thermal circuit protection include appliances, transportation, marine, switchboards, medical equipment, audio-visual equipment, power supplies, and sports equipment.

Magnetic Circuit Breakers

Magnetic circuit breakers provide a cost-effective solution to design problems with high accuracy and reliability. The overcurrent detection mechanism of magnetic circuit breakers responds only to changes in current in the protected circuit, and because their current sensing solenoid is not significantly affected by ambient temperature changes, magnetic circuit breakers are temperature stable and are not affected as significantly by ambient temperature changes as thermal circuit breakers.

Magnetic circuit breakers have no warm-up phase, which does not slow the circuit breaker's response to overloads, and there is no cool-down period from the end of the overload until it resets.

The characteristics of magnetic circuit breakers can be specifically adjusted in four separate areas: the circuit required by the circuit breaker; the trip point (in amperes); the delay time (in seconds) and the surge handling capability. Adjustments to these factors have minimal effect on the circuit breaker's short-circuit breaking capability.

Generally speaking, there are three types of magnetic circuit breakers available with different trip time delay curves: slow, medium, and fast. These selectable curves provide designers with great design flexibility when matching circuit breakers in cascade circuits and discrimination circuits.

In addition, for equipment that often needs to withstand large inrush currents, magnetic circuit breakers with special inrush structures can also be selected. However, when the equipment is in an unstable position, thermal circuit breakers may be a better choice because the trip times of magnetic circuit breakers will change due to the movement of the solenoid affected by gravity.