Although we have different types of electrical circuit breakers, they all do protective work. The switching device protects appliances from short circuits, ground faults, and power surge. It prevents electric shock and also protects the wiring system from a fire outbreak.
It is a must-have for every homeowner as required by the National Electrical Code.
Circuit breakers come in varying sizes and models, ranging from the low voltage interrupters used in homes to high voltage breakers used in substations. But they do the same work, which is overcurrent protection.
Circuit breaker types
There are three different types of circuit breakers, they include:
- Standard circuit breakers
- Ground fault circuit interrupters (GFCI).
- Arc fault circuit interrupters (AFCI).
1. Standard circuit breaker
These are the main breakers used in homes and industries to protect branch circuits and appliances from a power surge. It can be a double or a single-pole circuit breaker.
Single pole circuit breakers are more common, and they protect only one circuit. It also supplies 120V and handles between 12 and 20 amps.
The double pole circuit breaker has two single poles joined by a trip mechanism. It protects two wires, supplies 120/240V, and also handles 15 to 200 amps. It is used on large appliances such as a water heater.
Standard circuit breakers are further classified according to:
- the voltage level.
- External design type.
- Interrupting type.
Classification based on voltage level
The breakers are classified into three groups; they include:
- Low-voltage circuit breakers
- Medium voltage breakers
- High-voltage circuit breakers.
Low-voltage circuit breakers
This is the circuit breaker used in most homes, industries, and business areas. They are rated for use at a low voltage from 0 to 1000 V. Their examples include:
- Miniature circuit breaker (MCB): MCB can handle up to 125 Amp currents. This makes it suitable for domestic and business use. MCB is easy to use, but you can’t adjust its tripping load. They operate on thermal magnetic properties.
- Molded case circuit breaker (MCCB): MCCB can contain up to 1600 Amp currents, making it a better option for industries that need a higher power. And unlike MCB, we can adjust their own trip load.
Characteristics of a low-voltage circuit breaker
- You can repair it without losing its switchgear.
- Some are automatic, especially the molded case breakers. Thus, they can open and close under remote control.
- You can use it on direct current (DC) applications. For example, DC for subway lines. And unlike the alternate current, D.C. requires a special breaker as their arc continues.
Components of a low voltage breaker.
1. Actuator lever: Used to ON and OFF the breaker. Sometimes, a current trip off while the lever is at the ON position. Such is termed as trip-free.
2. Actuator mechanism: Opens and closes the contact.
3. Contacts: Allow current flow when closed and break the current when open.
4. Terminals: This is where breakers connect to the entire circuit.
5. Bimetallic strip: This separates the contacts when there is a high- voltage or short circuit.
6. calibration screw: It is what the manufacturers used to set the trip current after assembly.
7. Solenoid: Separate contacts when there is over current.
8. Arc extinguisher, or divider: This separates an arc each time a breaker interrupts light.
Medium voltage circuit breakers
Medium voltage circuit breakers handle voltages between 1 and 72 kV (1000 – 72000 V). You can use them indoors, or outdoors, in substations.
Indoor application circuit breakers have improved, they started with an oil-filled unit, to air-break, and now vacuum circuit breakers, which handle up to 40,500 V.
And like high-voltage circuit breakers, current transformers also control them via the current sensing protective relays.
Classification of medium voltage circuit breakers
Medium voltage breakers are classified by the medium they use to extinguish the arc. They include.
- Air circuit breakers: These breakers use air to extinguish the arc. It can house up to 6,300 Amp of current, and higher for generator circuit breakers. They have adjustable tripping features, configurable trip thresholds, and delays. They are controlled electronically, except for the microprocessor models, which are controlled by electronic trip units.
- Vacuum circuit breakers: They interrupt light by extinguishing the arc in a vacuum called a bottle. It also houses up to 6,300 amp of current and higher for generator circuit breakers. They have a longer life span and cause fewer environmental hazards than sulfur hexafluoride circuit breakers.
- Sulfur hexafluoride circuit breakers (sf6): This breaker extinguishes the arc in a sulfur hexafluoride-filled chamber.
High-voltage circuit breakers (72.5 KV & above).
This is the type of circuit breaker common in substations to protect electrical transmission networks from overload and earth faults.
They use solenoids, controlled by current sensing protective relays from the current transformers.
High-voltage circuit breakers can either be live or dead tanks.
In a live tank, the interrupter chamber (tank) is raised above the ground by an insulator, at a high potential. While in dead tanks, it holds the chamber on the earth’s metal.
Classification of high-voltage circuit breakers.
Classification of high voltage breakers is based on the medium they use to extinguish the arc. They include:
- Air or gas
Air or gas extinguisher
Air and gas extinguishers include the
1. Air-blast circuit breakers: This air blast came into existence in 1930s and became a common extinguisher for high voltage and high voltage applications.
It extinguishes the arc via compressed air stored in a tank. The tank produces high-velocity air when released. It cools and opens the arc.
2. Sulfur hexafluoride circuit breakers (SF6): SF6 is an inert gas with insulating and arc extinguishing properties.
They extinguish the arc by blowing a high-pressure gas on it. It cools and also separates the arc.
In vacuum interrupters, they house the contacts in a high vacuum that also acts as an extinguisher.
Vacuum extinguishers are more efficient, cheaper, and durable.
- Bulk oil interrupter: In bulk oil, the current interruption occurs inside the oil tank. The oil cools and separates the arc from each other, resulting in a blackout.
- Minimum oil: they use this in transmission and in substations, it requires less oil to function
This type of circuit breaker protects human beings from electrocution. It has a sensor that detects ground faults or leakage of currents. Each time there is leakage along the circuit, the outlet trips to prevent danger.
GFCIs are installed in kitchens and bathrooms where ground faults are common.
3. Arc fault circuit interrupters (AFCI).
This is a circuit protection device that trips each time there is a loose connection or arc-fault which may lead to a fire outbreak.
How to identify the right circuit breaker for your electrical system
If you want to replace your circuit breaker or install a new one, identifying the right one can be hard mostly for non-electricians. Below are the things to watch out for.
- Overall voltage rating: This is the maximum voltage it can handle before tripping.
- Current rating: It shows the value of currents the breaker can carry.
- Trip curve: This shows the graphical representation of the expected behaviour of a circuit protection device.