MCCB vs MCB: Understanding the Key Differences in Circuit Breakers

As solar PV systems become more widely used, the safety and reliability of the electrical circuits are now a major consideration. The function of the circuit breakers is to monitor the current flow and they are crucial role for tripping or turning off when an abnormal condition such as short circuits, overload, or ground faults is detected. This breaking of the electrical circuit prevents major hazards like fire, equipment damage or electrical shock.

In solar PV systems, different tiers of circuit breakers are installed from the array combiner boxes right up to the main distribution panels. Although fuses also provide basic protection, modern circuit breakers are resettable and modular devices that are far better in terms of flexibility, control and safety.

MCCBs and MCBs are the most common types of circuit breakers in AC power circuits of industrial plants, commercial buildings, residential electrical wiring devices and PV systems.

The two may have the same primary function but differ enormously in design, capabilities, and application. In this comprehensive handbook, we will cover the major differences between MCCBs and MCBs, so you will be able to make informed decisions for your solar PV installations.

What is an MCCB (Molded Case Circuit Breaker)?

An MCCB or Molded Case Circuit Breaker is an automatic protection device designed for low-voltage electrical systems. The main function of MCCB is to prevent and mitigate electrical faults caused by abnormal conditions such as short circuits or overloads, which can potentially damage the connected equipment and the power system.

The main feature of the MCB is its inherent thermal-magnetic trip functionality. It is made up of a moving bimetallic strip and a fixed contact. The bimetallic strip is in contact with the fixed point under normal conditions, and thus the current flows through the MCCB without any interruptions. Nevertheless, in case of overloading or short circuit occurring, a surge of current is produced, and the bimetallic strip is heated up and bent away from the fixed contact, thereby disconnecting the circuit. This process happens almost instantaneously, ensuring timely protection for the electrical system.

What is an MCB (Miniature Circuit Breaker)?

MCB or Miniature Circuit Breaker is a compact and lightweight automatic circuit protection device. MCBs are suited for residential, commercial, and space-constrained areas due to their small size.

The working principle of an MCB is almost similar to that of an MCCB, in which both devices use an internal tripping mechanism for automatic circuit interruption. While the tripping mechanism in an MCB is made up of a coiled bimetallic strip, the tripping mechanism in an RCCB is made up of a core of a magnetic material. In the normal state of things, the bimetallic strip stays in the closed position which allows the current to flow through. In the event of an over-current, the bimetallic strip will quickly coil and deform, causing it to bend and to break the circuit. Despite their small size, MCBs react with remarkable speed.

Key Difference 1: Current Rating

The operating current rating is one of the main parameters used for determining the type of circuit breakers. It is marked by the maximum current which can be continuously supplied without the breaker tripping.

The MCCBs are designed to work with higher capacity for current loads, with their ratings starting from 15A and going up to 2500A. This flexibility grants them the ability to endure the requirements of industrial machinery, large-scale electrical systems, and critical applications that cannot tolerate any downtime.

On the other hand, MCBs are designed to work at lower currents that are usually seen in residential and light commercial settings. Their current ratings are usually below 125A. A C or D Curve MCB rated for 10A to 63A would be suitable to protect most of the light commercial branch circuits carrying lighting or motive power loads.

Key Difference 2: Voltage Rating

Another main difference between MCCBs and MCBs is their voltage rating.

In the case of standard AC systems, MCCBs usually have a higher voltage rating than the MCBs. MCBs are usually rated about 230/400V AC, while MCCBs are typically rated above 600V AC, and even up to 1000V AC.

Nevertheless, in solar PV systems where DC power is used, the voltage rating requirements for the components are not the same as in traditional AC circuits. The MCCB and MCB are made to be able to manage the higher DC voltage to accommodate the specific requirements of PV installations.

For MCBs employed in solar PV units, the DC voltage level can go up to 1000V DC or even higher. This higher voltage rating becomes particularly important when multiple PV modules are connected in series, resulting in elevated system voltages.

Similarly, the MCCBs used in solar PV applications may have high DC voltage ratings (reaching 1000V DC and above) to be safe and reliable in high voltage DC systems.

Key Difference 3: Interrupt Capacity

The interruption capacity, or the interrupting rating, is the maximum short-circuit current that a circuit breaker can safely interrupt without any damage to the breaker or creating a dangerous situation.

MCBs are capable of interrupting currents of tens of thousands of amps to even millions of amps, depending on their rating and the design. This allows them to isolate and clear large overcurrents that may be present on industrial scale equipment. In industrial applications, which are always prone to the occurrence of high fault currents, this capability is irreplaceable for the safety of the personnel and the reduction of equipment damage.

While MCBs may have a lower interrupt capacity, ranging from a few thousand amps to tens of thousands of amps, they are enough for the most of domestic and light commercial applications, where fault currents tend to be lower and more controllable.

Key Difference 4: Physical Size and Configurations

MCCBs clearly have a larger footprint relative to MCBs. Their heavier duty construction comprises ticker insulating housing, more robust internal mechanism and components tailored to manage higher energy duties.

Greater spacing dedicated for heat dissipation also caters for safely discharging higher energy flows expected in larger centralized feeder circuits. These cascading considerations contribute to bigger external dimensions for MCCBs ranging from 52mm width right up to 140mm for very high 600A units.

The corresponding compact dimensions of MCBs -like a 22mm wide single pole module – reflects concentration of lower rated load currents into their more tightly packed internals. Concentrated resistive assemblies or wound magnetic coils make full use of the miniaturized space in providing core protective functionality like overload sensing and magnetic tripping response.

Modern intelligent MCCBs also allow flexible configuration of multi-pole formats (2, 3, 4 Poles) within standardized frame sizes. This facilitates tailored protection for three phase feeders in an MCCB form factor keeping size and costs lower than having 4 single pole units. MCBs can also be piggybacked in limited modular blocks, but not to the same versatile extent possible on MCCB modular or fixed chassis.

Key Difference 5: Tripping Characteristics

All Circuit breakers trip or open their contacts upon detection of overload or short circuit faults. However, the trip characteristics vary between MCBs and MCCBs.

MCBs exhibit very fast and steep tripping curves. Minor overloads reaching 120-150% of rated current can result in near instantaneous tripping within milliseconds through the magnetic trip mechanism kicking in. These tight tolerance bands combined with ultrafast response seeks to isolate downstream appliance faults very quickly before catastrophic failure can propagate upstream.

In contrast, MCCBs prioritize providing a measure of forgiving “coordination delay”. This inhibits immediate tripping on starting currents or motor inrush transients up to 8x rated value for adjustable period of 500ms or more. Only if overload persists above 120% for coordinated time lag would thermal or magnetic MCCB releases activate to open contacts. The benefit here is avoiding unnecessary shutdown of larger motors and load starting current inrush.

Both MCCB & MCB devices integrate both overload thermal sensing and magnetic instant trip elements internally in what’s termed as “thermal-magnetic trip circuit”. But the relative performance emphasis and calibration philosophy for the two mechanisms materially differs based on intended circuit protection applications.

Key Difference 6: Application Areas

The specific applications for MCCBs and MCBs differ significantly due to their varying capabilities and design characteristics.

MCCBs are primarily used in industrial and commercial applications where high current, voltage, and interrupt capacity requirements are present. Some common application areas for MCCBs include:

• Industrial machinery and equipment
• Motor control centers
• Large commercial buildings
• Utility substations
• Large-scale solar PV installations

On the other hand, MCBs are more suitable for residential and light commercial applications where the electrical loads are relatively small and the current and voltage requirements are lower. Common application areas for MCBs include:

• Residential electrical distribution panels
• Small commercial buildings
• Light industrial settings
• Individual circuit protection for electrical devices

Key Difference 7: Installation Requirements

MCCBs are directly fixed and wired into standardized mounting strips or flanged chassis. Due to larger sizes, centralized MCCBs are usually pre-installed with adequate safety spacing inside properly ventilated Low Voltage distribution cubicles or switchboxes before shipping. Professional electricians normally wire power and control cables with simple nut/bolt connections when installing MCCBs.

MCBs utilize slide-on type finger cluster terminals for fast plug-in installation. Modular MCBs can be conveniently retrofitted by electricians in the field across available DIN rail channels inside existing power panels, even in restricted spaces.

Key Difference 8: Maintenance and Lifespan

MCCBs used widely in commercial and industrial settings require routine detailed inspection and preventative maintenance recommended every 3 to 5 years. Qualified personnel verifies integrity of wiring, connections; proper contact alignment and evidence of any persistent overheating. Lubrication of moving linkages, resets of adjustable tripping thresholds & replacing worn components ensures sustainable optimum performance.

Field MCBs generally feature sealed non-serviceable construction with no user maintainable parts internally. Replacement instead of refurbishment is recommended nearing expected device lifespan of 10 to 15 years depending on operating environment. Harsher installation conditions like moisture, corrosive gases or elevated temperatures degrade lifespan. Negligible maintenance therefore traded off for shorter replacement cycles in MCBs.

Key Difference 9: Cost Comparison

MCCBs bear 25% to 50% cost premium over standard MCB models of equivalent current rating for few key reasons:

• Larger physical materials and components add cost
• Higher grade conductors handle greater currents
• Superior insulation and molding material quality
• More sophisticated tripping mechanisms
• Greater R&D and compliance testing behind assured interrupting capacity

The cost premium however returns benefit via assured performance integrity and capabilities to support larger plant infrastructure securely. For smaller downstream duties though, such lavish overspecification becomes harder to justify economically. MCBs ici offer reliable protection more affordably for branch circuits in lighting, utility or motive loads.

How to Select Between MCCB and MCB?

I recommend 4 key criteria while differentiating MCCB vs MCB selection:

• System voltage rating of supply feeders
• Required current rating based on connected load
• Short circuit capacity available at interfacing points
• Accessibility for future maintenance and lifespan considerations

Use MCCB when	Use MCB when	Hybrid Approach
– High short circuit currents above 10kA need interrupting – Load current exceeds 100A rating of typical MCBs – Custom protection curves or adjustable settings are needed – Reliable long term performance over decades is necessary	– Space constraints prevent installing larger MCCB – Quick low cost installation is the priority – Simple fixed thermal magnetic protection is adequate – Limited short circuit currents below 10kA – Branch circuits or single phase 120V/230V loads	MCCBs for main distribution equipment; MCBs internally for individual control panel components and small motor branches.

What about RCD, RCCB and RCBO?

In addition to MCCBs and MCBs, there are other types of circuit protection devices that are commonly used in solar PV installations, such as Residual Current Devices (RCDs), Residual Current Circuit Breakers (RCCBs), and Residual Current Breakers with Overcurrent Protection (RCBOs).

RCD or Residual Current Device works by detecting any residual current leakage to earth/ground that is not balanced. A transformer senses small differential currents from Live to Neutral as low as 15-30mA. RCDs cut power supply very quickly under such residual current leakage faults, providing protection from shock hazards. They are mandatory for socket outlets in residences.

RCCB or Residual Current Circuit Breaker combines the functionality of a circuit breaker and RCD into one device. When residual current to ground is detected, the RCCB opens contacts cutting off current flow. Easy retrofits into existing consumer units makes them popular. However only Overload or Short Circuit thermal magnetic tripping remains available if RCD is faulty.

RCBO or Residual Current Breaker with Overcurrent offers twin benefit of Residual Current (RCD) and Overload-Short Circuit (MCB) protection intelligently clubbed in one modular device. Provides easy selective circuit disconnect if either ground faults or heavy overloads arise. Commonly used in modern homes & commercial spaces for utmost safety.

While MCCBs and MCBs don’t integrate RCD functionality natively, Residual current can be still measured via added external core balance Current Transformers connected to their frames. These can trip the breaker coil upon detecting unbalanced current leakage conditions.

Conclusion

Choosing between an MCCB and an MCB for your solar PV installation is a critical decision. While both breaker types help mitigate electrical hazards, making optimal selections tailored to your system needs ensures long term safety and reliability.

BENY: Trusted PV Protection Components Manufacturer

As a leading manufacturer of PV protection components, BENY offers a comprehensive range of MCCBs, MCBs, and other protection devices specifically designed for the solar industry. Please consult our technical experts to determine the right solution matching your system protection priorities.