What are Circuit Breakers and Alerting Devices?

Automatic protective devices, better known as circuit breakers, are a critical part of an aircraft’s electrical system. Circuit breakers are provided to minimize distress to the electrical system in case of wiring faults or serious malfunction of a system or connected equipment, and are paired with alerting devices that provide a visual or aural alarm to alert the pilot to the situation.

Circuit breakers are designed to open and close an electric circuit, and to open that circuit automatically at a predetermined overload current, without damaging any components. The purpose of a circuit breaker in an aircraft’s electrical system is to provide overcurrent protection for wires and cables and minimize the dangers of smoke, fire, and other threats to the safety of the passengers and flight crew. The correct circuit breaker can result in a protective devices with the lowest standard rating that will not accidentally trip. A circuit breaker must be able to interrupt the fault or overload current by disconnecting the faulted line from the power distribution point before any wire or insulation damage occurs.

Most circuit breakers can carry roughly 115% of their rated current indefinitely, with the excess to provide a tolerance for the effects of environmental conditions like wear, vibration, etc. The instantaneous trip current is typically in the realm of ten times the current rating of the circuit breaker. When selecting a circuit breaker for a particular application, variables like time-current characteristics, start-up surges, wire type, size and location, and the altitude the equipment will likely operate at.

Both magnetic and thermal circuit breakers are available, with thermal circuit breakers being the more popular variant. Thermal circuit breakers function off of the deflection of a bi-metal strip that will open the circuit at a predetermined temperature. Temperature rise in the sensing element is caused by the load current, but this can be affected by the ambient temperature.

Most circuit breakers are trip-free, meaning that they cannot be manually reset while an overcurrent circuit fault remains. Non-trip free circuit breakers are used when the application requires overriding the tripping mechanism, such as in an emergency. Trip characteristics can change after a long period of inactivity, so periodically operating the circuit breaker manually with no electrical load is recommended to prevent this from occurring.

At ASAP Purchasing, owned and operated by ASAP Semiconductor, we can help you find all the circuit breaker and alerting devices systems and parts for the aerospace, civil aviation, and defense industries. We’re always available and ready to help you find all the parts and equipment you need, 24/7-365. For a quick and competitive quote, email us at sales@asapsemi.com or call us at 1-714-705-4780.