Low Voltage Switchgear: How Many of These 5 Core Components Do You Know?

Low Voltage Switchgear: How Many of These 5 Core Components Do You Know?

Introduction

A low voltage switchgear looks like a metal box, but what really determines its performance and reliability are the core components inside. Many customers focus only on the enclosure and overlook these "internal organs."

If the components are poorly chosen or of low quality, even a nice-looking cabinet will experience frequent faults, tripping, or even burnouts.

This article introduces the 5 most common core components inside low voltage switchgear:

• Molded Case Circuit Breaker (MCCB)

• Air Circuit Breaker (ACB)

• Contactor

• Thermal Overload Relay

• Surge Protective Device (SPD)

Understanding their functions and selection tips will help you make better decisions when purchasing and maintaining your switchgear.

1️⃣ Quick Overview of the 5 Core Components

2️⃣ Molded Case Circuit Breaker (MCCB): The Guardian of Branch Circuits

One-line summary: Every branch circuit (motors, lighting, sockets, air conditioners, etc.) needs this for protection.

What does it do?

• Automatically cuts off the circuit when current exceeds the set value

• Protects cables and equipment from overload and short circuit damage

• Can be manually operated as a circuit isolation switch

Selection tips:

• Rated current: Choose based on load current – typically 1.2–1.5 times higher

• Breaking capacity: Must be higher than the prospective short-circuit current at the installation point (in some African regions, the grid short-circuit current can be high – we recommend high breaking capacity versions)

• Number of poles: 1P or 2P for single-phase circuits, 3P or 4P for three-phase circuits

Common fault: Frequent tripping → check for overload, motor fault, or undersized breaker

✅ Advice for African markets: Choose high breaking capacity MCCBs to cope with grid voltage fluctuations and unstable short-circuit currents.

3️⃣ Air Circuit Breaker (ACB): The Main Manager of the Incoming Supply

One-line summary: Installed at the main incoming end of the switchgear – responsible for overall protection of the entire panel.

What does it do?

• Carries and switches the total current of the entire panel

• Provides overload, short circuit, and earth fault protection

• Typically comes with an electronic trip unit – allows precise protection parameter settings

• Can be remotely operated (with motor mechanism)

Difference from MCCB:

• ACB: High current (630A–6300A), more functions, adjustable parameters

• MCCB: Lower current (10A–800A), simpler structure

Selection tips:

• Rated current: Calculate based on transformer capacity or total load

• Short-time withstand current: Higher is better – ensures selective coordination with downstream breakers

• Electronic trip unit: We recommend models with LCD displays for easy current monitoring and parameter setting

✅ Advice for African markets: For the main incoming ACB, we recommend well-known brands with electronic trip units to ensure accurate protection and easy commissioning.

4️⃣ Contactor: The Executor for Frequent Operations

One-line summary: Used for frequent switching of circuits – common in motor control, lighting control, air conditioner control, etc.

What does it do?

• Uses a small current to control a large current (e.g., starting a motor with a push button)

• Can be combined with push buttons, PLCs, thermostats for automatic control

• Suitable for frequent operations (tens or even hundreds of times per hour)

Selection tips:

• Rated current: Choose based on motor or load current – typically 1.5–2 times higher

• Coil voltage: Common options include AC 220V, AC 380V, DC 24V – must match the control system

• Mechanical and electrical life: Higher is better

Common faults: Coil burnout, contact welding → check for matching coil voltage and whether the load is too high

✅ Advice for African markets: If the power supply voltage is unstable, consider contactors with wide voltage range coils or add voltage stabilization measures.

5️⃣ Thermal Overload Relay: The Temperature Bodyguard for Motors

One-line summary: Specifically designed to protect motors from overload damage – typically used together with a contactor.

What does it do?

• Monitors motor current. When current exceeds the set value for a certain period, it automatically disconnects the contactor

• Has an inverse time characteristic – the higher the current, the faster it trips

• Can be manually or automatically reset

Difference from circuit breaker:

• Circuit breaker: protects cables and circuits

• Thermal relay: specifically protects motors (motors are more sensitive to overload than cables)

Selection tips:

• Current setting range: Must cover the motor's rated current – typically set to 1.0–1.2 times the motor rated current

• Coordination with contactor: The thermal relay should be mounted below the contactor, and their current ratings must match

✅ Advice for African markets: Thermal relays are relatively easy to damage. We recommend keeping several common size spares for quick replacement.

6️⃣ Surge Protective Device (SPD): The First Line of Defense Against Lightning

One-line summary: Protects equipment from damage caused by lightning strikes and switching overvoltages.

What does it do?

• When a transient high voltage appears on the line (e.g., from lightning or switching operations), it quickly conducts and discharges the overvoltage to the ground

• Protects sensitive loads downstream, such as electronic equipment, PLCs, VFDs

• Divided into Type 1 (direct lightning protection), Type 2 (induced lightning protection), and Type 3 (fine protection)

Selection tips:

• Discharge current: Higher is better. Type 1 uses 10/350μs waveform, Type 2 uses 8/20μs waveform

• Voltage protection level: Lower is better – indicates lower residual voltage

• Number of poles: Choose based on the earthing system (TN-C, TN-S, TT, etc.)

Common issue: SPDs fail without indication – we recommend choosing models with end-of-life indication or remote signaling contacts

✅ Advice for African markets: Many regions in Africa have frequent thunderstorms. We strongly recommend installing SPDs at the incoming panel – it is one of the most cost-effective lightning protection measures available.

7️⃣ Summary: Components Determine Switchgear Reliability

Conclusion

The reliability of a low voltage switchgear depends not only on the enclosure but also on the internal components.

• Molded Case Circuit Breaker (MCCB): Basic protection for every circuit

• Air Circuit Breaker (ACB): Core protection for the main incoming supply

• Contactor: Executor for frequent operations

• Thermal Overload Relay: Dedicated bodyguard for motors

• Surge Protective Device (SPD): First line of defense against lightning

Advice for customers:

1. When purchasing, ask clearly about component brands and models

2. For critical circuits (motors, main incoming), do not compromise on quality

3. In areas with frequent thunderstorms, always install SPDs

4. Keep spare stock of common components (thermal relays, contactor coils)

We supply complete low voltage switchgear panels and all matching components, all manufactured to international standards. If you have a project requirement, please contact us for configuration advice and a quotation.

Contact us：
Web: https://yqsxdl.en.made-in-china.com/
Whatsapp：+19518189858
Mail: lunahe927@gmail.com