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circuit breaker Basics | How it works

This page covers circuit breaker basics.It mentions circuit breaker application note and circuit breaker manufacturers or Vendors.

As we know circuit breaker is very essential device for our safety at home and offices. This device cuts off the supply of AC power to the premises when it notices any unexpected situations such as short circuit, equipment failures, heavy current in the electric wiring.

Without circuit breaker the life is in danger as it may lead to the fires. It may also damage costly equipments and other devices connected to the AC power lines during untoward situations.

circuit breaker Application Note

Before we move to details of how circuit breaker works, let us understand situations such as overload and short circuit which requires fuse and circuit breaker.

Overload: This situation occurs when more than one devices operate in single electric circuit. The overload situation can also arise when equipment is driven beyond its rated designed capabilities When this situation arises circuit should be shutdown or cut off by the over current protection device otherwise it will damage the equipments connected in the electric circuit line.

Short circuit: This situation occurs when low resistance path gets created due to touching of open conductors. Decrease in resistance results in short circuit current which will be thousand times greatet than normal condition current. Due to this heat gets generated and will often result into fire in the premises. Under this condition current should be immediately stoped flowing. This situation can be understood with the Ohm's law as explained below.

Ohm's Law describes the relationship of current, voltage, and resistance. For example, a 240 volt circuit with 24 Ω of resistance draws 10 amps of current. When a short circuit develops, resistance drops. If resistance drops to 24 milliohms, current increases to 10,000 amps.

To protect a circuit against over-currents, a protection device must detect the faulty situation and automatically disconnect the electrical equipment from the voltage source. An overcurrent protection device must be able to recognize the difference between overloads and short circuits and respond in accordingly. Small overloads can be allowed to continue for a short time, but larger overloads require quicker response, and short circuits must be interrupted instantaneously.

It is a one-shot device. The heat produced by overcurrent causes the current carrying element to melt open, disconnecting the load from the source voltage.

circuit breaker

Circuit Breaker: Circuit breakers provide a manual means of energizing and de-energizing a circuit and automatic overcurrent protection. Unlike fuses, which must be replaced when they open, a circuit breaker can be reset once the overcurrent condition has been corrected. Pushing the handle to the "OFF" position then back to the "ON" position restores the circuit. If a circuit reopens upon reset to the "ON" position, the circuit should be checked by a qualified electrician.

All circuit breakers perform the following functions:
• SENSE when an overcurrent occurs.
• MEASURE the amount of overcurrent.
• ACT by tripping in a timely manner to prevent damage to the circuit breaker and the conductors it protects.

Figure-1 depicts application of circuit breaker. As shown in the figure it is connected in series with the electric circuit. The Circuit breaker is usually in close condition and hence AC current is being provided to the motor. The Circuit breaker gets open when heavy current flows or short circuit condition occurs and hence prevent damage to the motor.

circuit breaker Manufacturers/Vendors

Following are the circuit breaker manufacturers or vendors:
• E.T.A.
• Altech Corporation
• LS Industrial Systems
• Precision Controls Co.
• Mechanical Products Co.
• Carling technologies
• Airpax
• Schurter electronics Pvt. Ltd
• American Electrical, Inc.

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