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When is a Circuit Breaker not a Circuit Breaker?

August 16th, 2010 1 comment

Question:  When is a circuit breaker not a circuit breaker?

 

Answer:   When it doesn’t trip and break the circuit.

 

This is not just a silly riddle.  It unfortunately is a fact of life.  Circuit breakers, either like the small ones in your home, or large industrial ones as supplied by MIDWEST, usually only trip when presented with an extra heavy load, or a short circuit.  This is great news.

 

But there is bad news also.  In the case of a poor connection somewhere in the circuit path, or a not-so-short short circuit, a circuit breaker will not trip.  To be specific, the electrical engineers at MIDWEST would say that the first case is a high impedance series circuit, and the second is a low impedance parallel circuit.  Either way, very significant heat can be generated in places where heat can cause a fire.  And because the current flowing can be below the trip value, the circuit breaker will not trip to break the circuit. 

 

Examples of a high impedance series circuit might be a loose screw on a lug, or poor wire nut connection, or a bad solder joint.  These essentially become an additional series resistive component in the circuit.   

 

Examples of a low impedance parallel circuit are carbonized arc paths on a printed circuit board, a bare wire brushing up against something it shouldn’t, or the failure of a normal load.  These essentially become an additional parallel resistive component in the circuit.   

 

All of these conditions can easily result in an electrical fire, or even a catastrophic arc flash.  In an industrial setting, one of the products that MIDWEST offers is arc flash and fire resistant Arc Flash Personal Protective Equipment.  MIDWEST also offers Infrared Scanning and Ultrasonic Scanning Services, which is a great way to locate the troublesome series or parallel faults causing dangerous high temperatures.

 

It is probably safe to say that most electrical fires can be attributed to a circuit fault with just the right impedance resulting in circuit current that does not trip the circuit breaker or blow a fuse.  Often these faults occur in out of way places such as walls or electrical sockets.   

 

So, when is a circuit breaker not a circuit breaker?   

 

Answer:  When the impedance of the circuit is such that the current is less than trip current, and the circuit breaker does not trip to break the circuit.