The safety and reliability of an electrical system are directly linked to the installed protection devices. They are responsible for protecting equipment, people, and facilities against faults, overloads, short circuits, electrical surges, and other operational risks.

In low and medium voltage electrical panels, there are several types of devices that act preventively and correctively, ensuring that the system operates within safety parameters.

In this article, you will learn about the main protective devices for electrical systems, their functions, applications, and characteristics.

1. Molded case circuit breaker

A molded case circuit breaker is a protective device that acts in disconnecting and protecting against overload and short circuits in low-voltage electrical systems.

One of the main advantages of this equipment is its versatility, as it can be configured in different ways, according to the project's needs.

Variations of the molded case circuit breaker:

• Disconnect switch: functions only as a disconnector, without electrical protection, allowing circuits to be opened or closed safely.

  
  

• TMF (Fixed Thermomagnetic): features factory-set thermal and magnetic triggers. Limited adjustment possibilities, but economical.

  
  

• TMD (Thermomagnetic Adjustable): protection against overload (thermal) and short circuit (magnetic), both with manual adjustment.

  
  

• TMA (Thermomagnetic with Extended Adjustment): features a wider and more refined adjustment of the short-circuit (magnetic) current, ideal for specific loads.

  
  

• Electronic: more precise and complete, it allows fine adjustments for overload, instantaneous short circuit, timed short circuit, ground function, among other protections.

  
  

• MA (Magnetic Only): short-circuit protection, without thermal protection. Widely used for transformer protection, where thermal protection is unnecessary.

2. Relays

Protective relays are intelligent devices responsible for monitoring electrical system variables and acting when abnormal conditions are detected, such as overload, short circuit, phase failure, earth leakage, internal arc, among others.

Main types of relays:

• Thermal relay: protects motors against overload. It operates slowly, simulating the heating of the conductors.

• Protection relays (digital or analog): provide protection against short circuits, phase failure, overvoltage, undervoltage, overcurrent, earth leakage, among others. They are configurable and widely used in medium voltage switchgear and more robust systems.

  
  

• Arc relay: specialized in detecting internal electrical arcs. It acts in milliseconds, shutting down the system before the arc causes major damage, protecting equipment and, most importantly, people.

3. Motor circuit breaker

A motor circuit breaker is a device that combines magnetic and thermal protection with disconnection, specifically designed for the protection of electric motors.

It provides protection against short circuits and overloads, and allows for manual disconnection of the motor, facilitating operations and maintenance.

4. SPD – Surge Protection Device

The surge protection device (SPD) protects the electrical system against transient surges, such as atmospheric discharges (lightning) or disturbances in the electrical network.

It works by diverting momentary overvoltages to the grounding system, protecting sensitive equipment from burning out or damage.

5. RCD – Residual Current Circuit Breaker

The RCD (Residual Current Device) is responsible for protection against electric shocks and current leakage to ground.

It compares the current entering and leaving the circuit. When there is a difference (leakage current), the device instantly trips, protecting people and preventing fires.

6. Open-circuit breaker

Open-frame circuit breakers are used in systems with very high currents, generally above 1600A, and can reach up to 6300A.

It offers high breaking capacity, precise adjustments, and complete protections — short circuit, overcurrent, grounding function, timing, and integration with automation systems.

It is widely used in distribution centers, main switchboards, and low-voltage substations.

7. Fuse disconnect switch

Device used for electrical disconnection with fuse protection.

Fuses provide quick and accurate protection against short circuits, while the switch allows for safe opening of the circuit for maintenance.

It is widely used in medium-voltage switchgear and transformers, especially in applications that require robust and reliable protection.

8. Miniature circuit breaker

Used in low-current circuits, miniature circuit breakers protect small residential, commercial, and industrial electrical installations against overloads and short circuits.

These devices are easy to install, low cost, and act quickly in abnormal conditions.

Electrical protection devices are essential for the safety and performance of systems. Each one plays a specific role, whether protecting people, equipment, or ensuring business continuity.