Industrial Circuit Breaker, a Different Device
When most people think of a circuit breaker they think of the little black switch that trips when they try to run the toaster and microwave at the same time. The industrial circuit breaker is a very different device. These can be similar in size and configuration to the common breaker but they can be as big as a room and operate at tens of thousands of volts and thousands of amps. There are several types available from a variety of manufacturers. Some common types are: molded case, insulated case, air frame, vacuum break and high pressure contact switches. These come in a multitude of sizes and configurations to meet just about any requirement.
Molded Industrial Circuit Breaker
Molded case breakers can range from 15A to 2500A and are generally smaller than the other types in the same amp range. Used in industrial power distribution systems, they are usually rated for 480VAC and have interrupting ratings around 100kA. Some manufacturers offer units rated up to 600V. Most larger breakers (over 100A) have thermomagnetic and electronic trip units.
Insulated case breakers are larger than molded case devices and come in current ratings from 800 to 6000A. These can be rated for up to 200kA interruption. Available accessories can include digital trip units with displays for information and diagnostics. These are often equipped with a drawout mechanism to make levering easier and safer.
Air frame circuit breakers are larger that the molded and insulated case breakers. These are often available in medium voltage ratings (600-2500VAC) not normally found in the smaller types. The air frame industrial circuit breaker is equipped with some kind of arc control to quench the arc when the breaker is opened under load. These generally use a stored energy system to open and close the contacts more quickly than is possible by hand.
Vacuum Industrial Circuit Breaker
Vacuum Circuit Breakers have the operating contacts enclosed in a vacuum to eliminate almost all the arcing when the contacts open or close. These are used on medium and high voltage applications up to 15kV (and sometimes higher). The narrow opening gap permitted by the vacuum makes these units very fast to operate(trip) in as little as three cycles.
High pressure contact switches can be used as circuit breakers with the proper sensing and tripping circuits. These are also called bolted pressure contact switches and are available with current ratings up to four thousand amps. They are very similar to the air frame breakers in that they use some form of stored energy for opening and closing the contacts. The high pressure bolted contacts provide an improved current carrying at high currents with less heating of the contacts.
Any modern industrial circuit breaker will have functional and safety features in addition to the basic function of simply opening a circuit. These features vary among manufacturers but can include digital displays and various adjustments. When replacing a failed circuit breaker be sure the replacement meets or exceeds the specifications of the original. When in doubt consult manufacturer’s websites or distributor’s sales engineers.
