Circuit Breakers

circuitbreakers A miniature or molded - case circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overcurrent or overload or short circuit. Its basic function is to interrupt current flow after protective relays detect a fault.

The circuit breaker is an absolutely essential device in the modern world, and one of the most important safety mechanisms in your home. Whenever electrical wiring in a building has too much current flowing through it, these simple machines cut the power until somebody can fix the problem. Without circuit breakers (or the alternative, fuses), household electricity would be impractical because of the potential for fires and other mayhem resulting from simple wiring problems and equipment failures.

A circuit breaker is used to provide stability and prevent cascading failures in distributed systems. These should be used in conjunction with judicious timeouts at the interfaces between remote systems to prevent the failure of a single component from bringing down all components.

Applications for Circuit Breakers:

Circuit breakers can be found in:

  • Home power
  • Lighting
  • Appliances
  • Power supplies
  • Uninterruptible power supplies
  • Power tools
  • High inrush motors
  • Transformers
  • Reactive loads
  • Medical diagnostic appliances
  • HVAC

Manufacturers

Altech
Carling Technologies
Delphi Connection Systems
E-T-A Circuit Breakers
Eaton
FCI / Amphenol
GE (General Electric)
Laird Technologies
Littelfuse
Omron
Phoenix Contact
Qualtek
Schneider Electric
Schurter
TE Connectivity

  • During normal operation, a circuit breaker is in the Closed state:
    • Exceptions or calls exceeding the configured callTimeout increment a failure counter
    • Successes reset the failure count to zero
    • When the failure counter reaches a maxFailures count, the breaker is tripped into Open state
  • While in Open state:
    • All calls fail-fast with a CircuitBreakerOpenException
    • After the configured resetTimeout, the circuit breaker enters a Half-Open state
  • In Half-Open state:
    • The first call attempted is allowed through without failing fast
    • All other calls fail-fast with an exception just as in Open state
    • If the first call succeeds, the breaker is reset back to Closed state and the resetTimeout is reset
    • If the first call fails, the breaker is tripped again into the Open state (as for exponential backoff circuit breaker, the resetTimeout is multiplied by the exponential backoff factor)
  • State transition listeners:
    • Callbacks can be provided for every state entry via onOpen, onClose, and onHalfOpen
    • These are executed in the ExecutionContext provided.