Selection, Coordination and Short-Circuit Protection for Industrial Circuit Breakers (MCCBs): Technical Reference

Introduction

Industrial Circuit Breakers (MCCBs) are critical components of manufacturing electrical equipment. Their correct selection, coordination and short-circuit protection affect the reliability and safety of electrical systems. Failure to perform these tasks correctly can result in malfunctions, production shutdowns, repair costs, and personnel hazards. This document provides a technical reference for the selection, calculation and use of MCCBs in industrial conditions, according to DSTU, EN, ISO and CE standards, UkrSEPRO.

Fundamental principles

MCCB circuit breakers perform overload and short circuit tripping functions. They use thermal and magnetic tripping to trip the circuit breaker when a threshold current is reached. The thermal trip mechanism uses thermal coil expansion and the magnetic trip uses a magnetic repulsive force that causes the breaker to trip at high currents.

Technical specifications and standards

The selection and use of MCCBs must be carried out taking into account the following standards:

• DSTU 3047-2011 — standards for electrical devices used in industrial production.
• EN 60947-2 - Standards for circuit breakers including MCCBs.
• ISO 281 is a standard for electrical switches, defining their technical characteristics.
• IEC 60947-2 is an international standard for MCCBs including tripping, endurance and safety requirements.
• CE, UkrSEPRO — certification that ensures compliance with Ukrainian and European standards.

Selection and calculation of MCCB

The selection of MCCB should be made taking into account the following criteria:

1. Rated current (In): must be greater than the maximum load current.
2. Maximum breaking current (Icu): must be sufficient to break a short circuit in the mains.
3. Temperature coefficient (K): affects the stability of the switch when the temperature changes.
4. Coefficient of recovery (Kv): determines the ability of the circuit breaker to resume operation after tripping.
5. Class of circuit breaker (Icu, Ics): determines the degree of protection against short circuit.

Optimum coordination of MCCB

MCCB coordination requires the following conditions:

• Distance between circuit breakers: the distance must ensure quick disconnection in the event of a short circuit.
• Difference in tripping currents: the difference between the Icu of the switches must be sufficient for correct coordination.
• Selection of switch stages: the stage of switches should decrease from main to sub-circuit.

Practical recommendations for installation and debugging

When installing the MCCB, it is necessary to:

• Check compliance with standards.
• Ensure correct connection to the electrical network.
• Adjust the circuit breaker to match the design parameters.
• Perform overload and short circuit trip testing.
• Keep the service log for future analysis.

General shutdown modes and basic operating modes

MCCB can work in the following modes:

1. Overload cut-off mode: the circuit breaker is cut off when the rated current is reached.
2. Short-circuit tripping mode: the circuit breaker trips when the short-circuit current is reached.
3. Recovery mode: The switch reconnects to the network after a shutdown.

MCCB models and their specifications

Below is a comparison table of three MCCB models that meet DSTU, EN, ISO standards and have CE, UkrSEPRO certification:

Shutdown modes and main operating modes

MCCB switches according to EN 60947-2 standards have the following modes:

1. Trip mode: the switch is tripped when the rated current is reached.
2. Recovery mode: The switch reconnects to the network after a shutdown.
3. Short-circuit tripping mode: the circuit breaker trips when the short-circuit current is reached.

Maintenance and recovery approaches

MCCB maintenance should be done according to the following recommendations:

• Periodically check the switch for compliance with standards.
• Perform overload and short circuit trip testing.
• Clean and lubricate the switch mechanisms.
• Keep the service log for future analysis.
• Replace the switch if defects are detected.

General shutdown modes and basic operating modes

MCCB can work in the following modes:

1. Overload cut-off mode: the circuit breaker is cut off when the rated current is reached.
2. Short-circuit tripping mode: the circuit breaker trips when the short-circuit current is reached.
3. Recovery mode: The switch reconnects to the network after a shutdown.

Maintenance and recovery approaches

MCCB maintenance should be done according to the following recommendations:

• Periodically check the switch for compliance with standards.
• Perform overload and short circuit trip testing.
• Clean and lubricate the switch mechanisms.
• Keep the service log for future analysis.
• Replace the switch if defects are detected.

Status monitoring and recovery

The following methods can be used to restore the MCCB:

• Thermal monitoring: measuring the temperature of the switch.
• Magnetic monitoring: circuit breaker current measurement.
• Relay Control: Using relay devices to control the circuit breaker.
• Optical control: use of visual indicators to detect deviations.
• Data Analytics: Using Data to Predict Circuit Breaker Recovery.

Conclusion and purpose

Industrial MCCB circuit breakers are critical components of electrical equipment. Correct selection, coordination and short-circuit protection ensure the reliability and safety of electrical systems. For more information on components and products that meet DSTU, EN, ISO, CE, UkrSEPRO standards, visit our e-catalog.

Sources

1. DSTU 3047-2011 — Standards for electrical devices.
2. EN 60947-2 - Standards for circuit breakers.
3. ISO 281 - Standards for electrical switches.
4. IEC 60947-2 - International standards for MCCB.
5. CE, UkrSEPRO — Certification of compliance with standards.