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Controlling Current in Electric Circuits

The amount of electric current passing through a circuit depends on the voltage pushing the current and the resistance opposing the current.

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Circuit Breakers

Circuit Breakers

Credit: e.res
Source: http://www.flickr.com/photos/iamtheloop/242081320
License: CC BY-NC 3.0

Similar to a fuse, a circuit breaker interrupts the flow of current if safe operating conditions are passed.

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  • Circuit breakers are similar to fuses in that they interrupt the flow of current in a circuit if the current in a system becomes too large. 
  • Unlike fuses though, circuit breakers can be used more than once. 
  • Circuit breakers in their simplest form consist of a bimetallic strip or an electromagnet and a switch. In the case of the electromagnet or magnetic circuit breaker, the pulling force of the electromagnet increases as the current in the circuit increases. When the current in the circuit exceeds the safety rating of the circuit breaker, the electromagnet releases a latch causing a spring to move the contacts in the circuit, breaking the current.
  • While there are many different types of circuit breakers using in the world, they all follow the same basic steps:
    1. A fault must be detected. (A fault is a condition/variable that is being monitored)
    2. When a fault is detected or if the current is too high, contacts within the system must open to prevent the flow of current.
    3. When the current is interrupted, an arc of electricity is created. The circuit break components must be able to prevent the arc from damaging its components.

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Using the information provided above, answer the following questions.

  1. If a 5 V toaster has a resistance of 1 omh, would it blow a 3 amp fuse?
  2. If a 10 V appliance is able to run when connected to a circuit that is protected with a fuse rated for 20 A, what is the minimum resistance that the appliance could have?

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Image Attributions

  1. [1]^ Credit: e.res; Source: http://www.flickr.com/photos/iamtheloop/242081320; License: CC BY-NC 3.0

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