You might not realize it, but circuit breakers are what make it possible to run your coffee maker or put humans on the moon. These switches sense that you are pushing more energy-demanding electricity than the wires or fuses can handle and open the circuit before the wires begin to heat up and melt insulation.

Electromagnetic

Circuit breakers are a vital part of the electrical systems that power our homes, businesses and industrial buildings. They are designed to interrupt current flow when too much is flowing through devices and can prevent fires, electric shock and electrocution.

When a short occurs, the metal contacts inside a circuit breakers open to interrupt the current. But if the current continues to flow, it can create an electric arc that can burn through the contacts and erode the internal components. The metal contacts also require enough strength to withstand the heat of this arc. This is accomplished with an electromagnetic component called an electromagnet that is powered by a flowing electrical current. The current passes through an insulated wire wrapped around a coil that forms the magnetic field.

Bimetallic

Thermo-mechanical breaker elements use two different metals with differing coefficients of linear thermal expansion, bonded together lengthwise. When electrical current that exceeds the breaker-overload rating passes through, it heats up the bimetallic strip and bends it, operating a linkage to unlatches a spring-operated contact and interrupting the circuit.

This type of breaker can be manually reset after the excess current has cooled down. It is also commonly found in shaving sockets because of the small current that it can handle. Electromagnet-based breaker elements use an electromagnet that responds to varying levels of electric currents by changing the field strength. When the electromagnetic field reaches a certain level, it attracts a magnetic coil attached to the armature and rotates the trip bar, causing the contacts to open, interrupting the circuit.

Hydraulic Fluid

A circuit breaker's hydraulic fluid field is a safety feature that keeps the arc from heating too quickly. The arc is caused by current flow and the heat that it generates, which can pit (transfer metal from one surface to another) or destroy electrical contacts and insulating materials.

There are many types of hydraulic fluids used in low and medium voltage air circuit breakers. Phosphate ester-based synthetic fluids are a popular choice because they don't contain any fire hazards and offer outstanding lubrication properties.

Modern breaker panels can also be field programmable to achieve specific responses to different values of current and time. This type of breaker allows for the most precise adjustments possible. However, remember that electricity is not a toy and must always be treated with care and respect. Proper lockout-tagout procedures and personnel protective equipment should always be in place when working on anything above 50 volts.

Explosive

There are many types of circuit breakers used today. They operate differently, but they all do the same basic job: cutting off power to appliances when too much current is flowing.

The breaker has to be able to respond very quickly to an abnormally large current flow (called a short circuit). In some cases, the maximum prospective short-circuit current can be many times the normal rated current. When electrical contacts open to interrupt a very large current, there is a tendency for an arc to form between them. To prevent this from happening, circuit breakers incorporate features to divide and extinguish the arc. Miniature low-voltage breakers use air alone; larger ratings have metal plates or nonmetallic arc chutes to divide the arc and allow it to cool.