When choosing protective devices for equipment design, designers face various problems. They must choose from components such as fuses, electromechanical and circuit breakers, as well as special segmented market replacement protection equipment. They must also consider safety as it can affect equipment, personnel, and the environment. Finally, designers must evaluate the impact of factors such as initial cost, lifecycle cost, reliability, safety, convenience, warranty, and company image on profitability. In many applications, device circuit breakers (CBE) can provide solutions to these problems (see box).

To merge CBE into any part of an electronic system, please consider the following criteria:

*Determine what types of malfunctions may occur in the equipment to be protected. Match the overload characteristics of the device with the performance of an appropriate CBE.

*View all extreme environments that the system will see and their impact on CBE selection, including temperature, shock, and vibration.

*Determine if other functions are needed, such as visual indicators, switches, or auxiliary circuits.
*Estimate the possible fault current level that the circuit may encounter as accurately as possible.
*Determine how quickly CBE must react before device, component, or circuit damage occurs.
*If you decide to use CBE, please ensure that the circuit fault conditions include CBE resistance when calculating the potential, as it may greatly limit the circuit fault current.
*To determine the rated current of CBE, always determine the maximum operating current in the circuit and ensure that the circuit breaker does not trip. So, this value is the rated current of the CBE that should be selected. This rated value is marked on the device button or the body of the selected CBE.

*Search for existing international approvals.

The internationally recognized IEC 934 standard defines three main CBE types (R, M, and S) for equipment circuit breakers, each with a complete tripping mode: the R type will automatically disconnect when overloaded and must be manually reset. The M-type is not a switch used for conventional purposes, but it can sometimes be used to turn on/off manual switches. The S-type combines automatic overload disconnection with conventional manual on/off switching under normal load conditions. CBE designated as S-type in the IEC934 standard is a true combination switch/circuit breaker. The S-type can combine switches, circuit breakers, and lighting (lamps) together in a single package (see Figure 1). This means that there is no need to separately purchase, stock, and install the three components. This also saves space. These types of CBE look like standard on/off switches, providing options such as auxiliary contacts and undervoltage release in addition to lighting. The circuit protection is not affected at all. In the event of a malfunction, these CBEs will automatically switch to the closed position and cannot be forcibly overwritten.