A comprehensive guide on industrial circuit breakers
An industrial circuit breaker is an automatic electrical switch that is designed to protect electrical circuits from damage due to overcurrent caused by overloads and short circuits.
Unlike fuses, industrial circuit breakers can be reset after they trip. This unique feature makes them important for keeping operations safe and reducing downtime in places like factories, data centers, and power plants.
This technical guide aims to provide a clear understanding of industrial circuit breakers in industry by elaborating on their working step-by-step mechanisms, various types, and crucial selection criteria.
Why do we need circuit breakers?
Industrial circuit breakers play a crucial role in protecting electrical systems against overcurrents, which can cause overheating, equipment damage, electrical fires, and even injuries. These devices automatically cut power when the current surpasses safe levels, thereby protecting circuits and ensuring operational safety. Selecting the right circuit breaker in system design prevents costly reworks and improves the durability and performance of the entire setup.
Working mechanism of industrial circuit breakers
Circuit breakers automatically interrupt the current in an overloaded circuit by tripping when protective relays encounter a fault. Every circuit breaker working mechanism involves five common components:
- Frame: These molded frames act as an outer protective case which safeguards the internal components of the circuit breakers from outside materials.
- Operative mechanism: This allows it to fulfill its protective role by opening or shutting the breaker as per the requirement.
- Contacts: Allows the current to flow through the circuit breakers in normal conditions. They can be mainly divided into three types, i.e., arcing, auxiliary and main contacts.
- Arc extinguisher: This system is designed to extinguish the electrical arc that forms when the breaker’s contacts open to interrupt a fault. It uses arc chutes to safely dissipate the heat and quickly extinguish the arc, ensuring safe and reliable circuit interruption.
- Trip unit: This triggers the operating mechanism once an electrical fault happens.
Figure 1: Parts of circuit breaker (Source)
Types of industrial circuit breakers
Circuit breakers are widely used in residential, commercial, industrial, avionic, military, and other electrical settings. In this article, we will focus on the industrial types. These can be of different types depending on operating mechanisms, voltage levels, and arc-quenching medium.
- Molded case circuit breakers (MCCBs)
- Miniature circuit breakers (MCBs)
- Hydromagnetic circuit breakers
- Thermal circuit breakers
- Electronic circuit breakers
- Air circuit breakers (ACBS)
Molded case circuit breakers- MCCBs are safety devices that protect electrical circuits by automatically interrupting power during overloads or short circuits, preventing system damage. It can detect the difference between overload and short circuit. To protect electrical devices from serious damage, MCCBs allow a small amount of overcurrent for a short time, and as soon as the current level rises, a thyristor opens the circuit to prevent harm. They are versatile for both low and high-voltage applications and offers adjustable trip settings.
| Types | Applications | Features |
|---|---|---|
| Type B: Trips at 3-5 times the rated current (0.04-13 sec). | Best for low surge and resistive loads. | Available in single, two, three, or four-pole versions, with adjustable tripping mechanisms for increased safety. Rated for currents between 10 to 200 amps. They are designed to handle high-power demands, making them ideal for heavy current circuits in industrial settings. |
| Type C: Trips at 5-10 times the rated current (0.04-5 sec). | Common for small motors and transformers in industrial settings. | |
| Type D: Handles 10-20 times the rated current (0.04-3 sec). | Best for large motors and heavy inductive loads. | |
| Type K: Trips at 10-12 times the rated current (0.04-5 sec). | Suits for motors with inductive loads. | |
| Type Z: The most sensitive, trips at 2-3 times the rated current. | Used for delicate electronics like medical equipment. |
Figure 2: Molded Case Circuit Breaker from EATON (EATON CUTLER HAMMER EGH3060FFG) (Source)
Miniature circuit breakers (MCBs)- These are automatic switches that turn off the power supply when they detect a power surge. MCBs are equipped with two tripping mechanisms: a delayed thermal tripping mechanism for overload protection and a magnetic tripping mechanism for short circuit protection. Based on their tripping capacities various types of MCBs are available to match different industrial applications.
| Types | Applications |
|---|---|
| Type C and Type D | 1.Electrical Panels: MCBs provide consistent power distribution and control fluctuations. 2.Lighting Systems: These regulate power for lighting and enhance bulb lifespan. They ensure residential safety if different lights are fitted in different areas in the home. 3.Industrial Equipment: MCBs handle heavy loads (up to 30 kA). They are commonly used in supermarkets, hotels, and malls where they protect valuable industrial equipment, 4.Ground Fault Protection: They prevent surges from ground faults by automatically cutting power, reducing the risk of hazardous incidents. |
Figure 3: Miniature Circuit Breaker from ABB (Source), product- ABB S202-C20(Source)
Hydromagnetic circuit breakers- A Hydraulic Magnetic Circuit Breaker provides precise overload and fault protection using a solenoid-based mechanism. The mechanism of a Hydraulic Magnetic Circuit Breaker includes a current sensing coil paired with a set of contacts. All of these contacts remain closed during regular operation. In case of an overload (current exceeds the rated capacity), the series coil generates a magnetic flux, which moves a core within a fluid-filled tube, thereby tripping the beaker. The core, pulled by the greater magnetic force , release the lock and disconnects the circuit. These beakers offer fast, reliable protection against current surges without relying on temperature-sensitive components.
| Features | Application areas |
|---|---|
|
|
Figure 4: SENSATA / AIRPAX IELK111-1REC5-62-100.-A-01-V (Source)
Thermal circuit breakers- Thermal circuit breakers protect circuits by using a bimetallic strip that bends when overheated, interrupting the flow of electricity. As the current increases, the strip heats up and trips the breaker when it exceeds the set limit. Once the strip cools, it can be manually reset. While they are reliable and often function as main on/off switches, thermal breakers are sensitive to ambient temperature, causing nuisance trips in warm conditions or delayed tripping in cold ones. They're usually fitted in automotive wiring and other low-voltage circuits. A thermal actuator and a mechanical latch work together to distinguish between short bursts of high current and longer periods of overload. This means the system can handle a temporary surge without tripping. However, if the current stays too high for too long, the latch will activate to protect the equipment from damage.
| Types | Features | Reset mechanism | Applications |
|---|---|---|---|
| Automatic reset | Cycles or continuously resets until the fault is corrected. Used in circuits with momentary overloads, like wiper motor or headlamp circuits. | Automatic | Wiper motors, headlamps |
| Modified reset | Non-cycling. Circuit remains open after tripping. Resets when power is turned off. Common in applications like power window and sunroof circuits. | Modified reset (power off) | Power windows, seats, sunroofs |
| Manual reset | Non-cycling. Remains open until manually reset by pressing a button or lever. Typically used where safe diagnosis is necessary. | Manual | Circuits requiring manual fault diagnosis |
| Manual reset - push to trip | User can manually press a button to open the circuit after resetting. Provides manual trip capability. | Manual with trip button | Systems needing manual trip option |
| Manual reset - switchable | Allows the user to switch the circuit ON or OFF using an external lever. Functions like a switch. | Manual with lever switch | Switch-like functionality in circuits |
Figure 5: Thermal Circuit Breaker ETA 3120-N521-H7T1-W01D-20A, On-Off, 3120-N Series, 20 A, 2 Pole, 50 V, 240 V, Snap In (Source)
Electronic circuit breakers- Electronic circuit breakers use specialized components to monitor the current and voltage in a circuit. During an overcurrent condition, the breakers instantly send a signal to a gate in a solid-state device (such as a thyristor), which quickly opens the circuit. These breakers can be customised for different settings. Electronic circuit breakers. ECBs are frequently found in complex systems, where they combine a high switch-on capacity with an electronic relay for higher effectiveness.
| Key Features | Main Advantages |
|---|---|
|
|
Figure 6: Electronic Circuit Breaker (Source)
Air circuit breakers (ACBs)- An Air Circuit Breaker (ACB) is a crucial component in low-voltage electrical systems. They are designed to protect circuits from overcurrent and short circuits. Using air as the medium to extinguish arcs, ACBs can handle currents from 800 to 10,000 Amps in systems below 450V. They operate with stored energy, using springs to quickly open and close contacts when needed. ACBs are widely used for safe circuit interruption in distribution panels, with metallic arc chutes helping to cool and split the arc for effective protection.
| Types | Advantages | Applications |
|---|---|---|
| Plain Break Type ACB (Cross-Blast ACB) | Simple design, suitable for low voltage applications, cooling with arc chute. | Used in low voltage applications. |
| Magnetic Blowout Type ACB | Magnetic control for arc extinction, used up to 11KV | utilised up to 11kV, suited for medium voltage systems |
| Air Chute Air Break Circuit Breaker | Low contact resistance, heat-resistant arcing contacts, high durability. | Used to protect main contacts in systems, suitable for medium voltage applications. |
| Air Blast Circuit Breaker | High-speed operation, fast arc quenching, less maintenance, no fire hazards. | Used for systems above 245KV, ideal for quick breaker operations in large plants. |
Figure 7: Air Circuit Breaker (Source)
Key considerations for selecting industrial circuit breakers
Electrical safety and system efficiency is realized only when the specific needs of that application, as only a right selection results in optimal circuit protection. It also results in
Voltage rating- While selecting a circuit breaker, it’s important to make sure the voltage rating matches the system requirements. The voltage rating refers to the maximum voltage level that the breaker can safely handle across all ends and ports. This rating is influenced by the system’s distribution type and how the breaker is integrated. If the circuit breaker’s voltage capacity and the system’s voltage levels don’t match, then it can be triggered to safety risks. That is why it is essential to choose a breaker with adequate voltage capacity for the specific application.
Voltage range Circuit Breaker type Use areas Within 1KV MCB and MCCB General industrial and commercial sectors 1KV – 72KV Air, vacuum, and sulfur hexafluoride (SF6) Power generation and distribution, factories, office buildings, and data centers. Greater than 72KV Hydromagnetic, air blast, Oil circuit breakers Power transmission networks & circuits Continuous current rating- This is the maximum current the breaker can safely handle continuously under its calibrated ambient temperature (standard manufacturing ambient temperature is 104° F). Choosing a breaker with a current rating that matches the system load is essential. The breaker's amperage rating thus must match the circuit's maximum load. if the rating is too high, the breaker may fail to trip during overloads, risking overheating and equipment damage. Conversely, the breaker may also trip due to a too low rating, resulting in unwanted interruptions. An optimal protection and to create a reliable system.
Maximum interrupting capacity- The interrupting capacity (AKA breaking capacity), is a crucial factor when selecting a circuit breaker, especially in systems where high fault currents are highly possible. It represents the maximum fault current the breaker can safely interrupt without being damaged. For safety and reliability, the interrupting capacity of the breaker must be equal to or greater than the potential fault current at its point of application. As larger appliances and industrial systems demand higher fault current protection, selecting a breaker with sufficient interrupting capacity ensures the system can handle fault conditions without risking repeated trips or equipment failure. The table below represents typical ratings for 800 and 1600-amp frame MCCBs, ICCBs, and LVPCBs.
Type of Device MCCBs ICCBs LVPCBs Low IC High IC Low IC High IC CL Low IC (Internal Inst. Trip) High IC (Internal Inst. Trip) CL (Internal Inst. Trip) Low IC (No Inst. Trip) High IC (No Inst. Trip) Interrupting Capacity (kA @ 480 V) 50 100 50 150 150 30 100 200 30 85 Instantaneous Override or Max. Short-time Current Rating (kA) 6-9 6-9 25 25 30 30 85 30 30 85 Short-time Delay 18 18 30 30 30 30 30 30 30 30 Frequency- When selecting a circuit breaker, it's important to match its frequency rating with that of your electrical system to avoid inefficiencies or potential damage. Circuit breakers rated for 50-120 Hz can handle most applications, but higher frequencies (above 120 Hz) will require derating to account for increased heating from eddy currents and iron losses. For higher amp ratings, especially above 600 amps, proper calibration is essential to ensure safe operation, particularly in projects using 50 Hz or 60 Hz systems like diesel generators. The breaker's frequency compatibility must be checked for optimal performance and longevity.
Number of poles- The number of poles within a circuit breaker determines the number of separate circuits it can protect. Single-pole breakers are common in residential settings, while industrial applications typically use multi-pole breakers for three-phase systems. A 3-pole breaker is used to protect all three phases in such systems, while a 4-pole breaker adds an extra layer of protection by also disconnecting the neutral wire, which is critical in systems with unbalanced loads or harmonic currents. Choosing the correct number of poles ensures proper protection based on the complexity and needs of your electrical system. For instance, if you have a 3-pole, 600 A breaker and one pole has 800 A while the other two have no load, the breaker will trip because one pole exceeded its limit.
On the other hand, if all three poles have 500 A each, the breaker will stay on even though that totals 1500 A. This is because none of the individual poles are over their 600 A rating.
Specific operating conditions- Particular operating conditions and environmental resistance must be considered for reliable performance. The functionalities of the breaker can be influenced by high temperatures, corrosion, shock, altitude, and dust. For example, a typical breaker can operate up to 122°F, but derating or recalibration can be needed for higher temperatures. In humid or corrosive environments, moisture-treated or chemical-resistant breakers are necessary to prevent damage. Breakers in high-shock areas, such as marine applications, need anti-shock devices, while those used above 6,000 feet require derating due to thinner air's reduced heat dissipation. By accounting for these factors, you can choose a breaker suited to withstand harsh conditions and ensure safety and efficiency.
Compliance and standards- When selecting circuit breakers, it's crucial to ensure they meet the necessary industry standards and regulations, such as IEC, ANSI, or UL. By adhering to these standards, you can have confidence in the quality and effectiveness of the circuit breakers you choose. Some of the key ones are shown in Table 2-
Standards Covers UL 489 Molded-Case Circuit Breakers, Molded-Case Switches and Circuit Breaker Enclosures UL 1077 Supplementary Protectors for use in Electrical Equipment UL 60950-1 Information Technology Equipment: General Requirements NFPA 70 National Electrical Code (USA) CSA22.2 National Electrical Code (Canada) BS7671 National Electrical Code (UK) IEC 60364 Electrical Installations for Buildings (EU) IEC 60947-2 Circuit Breakers for Industrial Applications IEC 60898-1 AC low-voltage circuit breakers IEC 60934 Circuit breakers for household applications, including appliances SAE J553 Test conditions, procedures, and performance requirements for circuit breakers in transportation applications Table 2: Some applicable circuit breaker regulatory standards (Source)
Conclusion
Circuit Breakers offer precise, reliable, and cost-effective solutions to most design challenges. These are considered temperature stable, and their overcurrent sensing mechanism reacts only to changes in current in the circuit being protected. They are available with multiple configuration options, and many offers advanced features and cutting-edge designs to meet today’s leading application requirements. As a global distributor, Farnell offers a wide variety of circuit breakers to combat different requirements and ensure high performance across multiple industries.
