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Circuit Breaker Technical Information


Circuit Breaker

Who invented them? When? Why? The history of circuit breakers is the history of electricity. Circuit breakers appeared at about the same time as electrical power for industrial use. That would be at the end of the 1800s and beginning of the 20th Century.

Until very recently, electrical circuit breakers were very basic devices. If the current through the circuit breaker exceeded a certain level (rating), the circuit breaker would eventually "trip" open. It may surprise you to learn that circuit breakers do not trip immediately when the current exceeds their overload rating. In some cases the time delay can be several minutes, depending on how much the current exceeds the circuit breaker rating. Circuit breakers are manufactured with an intentional time delay. Most breakers also have an "instantaneous" function. But the instantaneous function does not trip the breaker unless the current through the circuit breaker is extremely high, possibly 20 times the circuit breaker's overload rating. The actual operation of some molded case circuit breakers was unpredictable. The trip delay of most molded case circuit breakers had a very wide range. As much as 50 to 300 seconds. Air circuit breakers had a variety of methods to provide protective trip rating and time delay. Some circuit breakers had oil dashpots. Some used springs and gears. Many modern molded case circuit breakers, insulated case circuit breakers, power circuit breakers, and low voltage air circuit breakers use electronic controls to monitor the current and trip the circuit breaker. These circuit breakers are very accurate and provide a major improvement in the quality of protection provide by a circuit breaker.


Circuit Breaker History

Year Event
1902 Manufacturing Company starts manufacturing fuse links.
1904 Cutter Manufacturing Co., located in Philadelphia, produces circuit breakers. The firm introduced a product that became an industry success. The new protective device, first promoted as the Inverse Time Element breaker, came to be known as the I-T-E breaker.
1921 Merlin Gerin manufactures first high voltage oil circuit breakers.
1925 NEC- Circuit breakers required to be enclosed and externally operable.
1928 Cutter name changed to I-T-E Corp. (From EC&M Magazine)
1932 Westinghouse begins marketing their modern molded case air circuit breaker.
1935 Square D manufactures first circuit breakers for use in homes.
1951 Square D introduces plug-in circuit breakers.

Click on question marks below to get answers to these frequently-asked questions.

What is the basic definition of an electric circuit breaker?

Help! We have circuit breakers, specifically molded case circuit breakers, everywhere in our plant. We perform little or no maintenance of our electrical equipment and circuit breakers. What would you recommend as the single most important and least expensive maintenance service on our circuit breakers? We have 2000 amp main circuit breakers; 400 amp feeder circuit breakers; I-Line circuit breakers; Mostly three pole 480 volt circuit breakers.

Can you recondition molded case circuit breakers after they have been rained on or even submerged in water? We were told you could not even take the cover off a molded case circuit breaker.

I need to extend power to a ‘new’ area. I have looked at different brands and compared the prices of new, available, circuit breaker boxes. I also found that I can obtain a clean, used, circuit breaker cabinet that already has some circuit breakers in it for a lot less than the cost of a new circuit breaker panel that does not come with any circuit breakers. What should I look for when comparing a new electrical breaker panel vs. a used, circuit breaker panel?

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