A Practical Guide to Earthing Switches: Function, Components, and Installation

Indoor earthing switches are an indispensable safety component in medium and high-voltage power systems. Designed to protect both operators and equipment, they are an essential mechanical device within modern switchgear. By providing a reliable path to dissipate residual charges, they serve as a critical line of defense for the personal safety of on-site personnel.

1. What is an Earthing Switch and How It Works?

An earthing switch in switchgear is a mechanical switching device used to safely ground a de-energized part of a circuit. It is capable of withstanding current under abnormal conditions (such as a short-circuit current) but is not required to carry the normal operating current. This characteristic makes it a key safety component in medium and high voltage switchgear.

Our indoor earthing switches are specifically designed for medium voltage switchgear operating at 12kV to 40.5kV and below, with an AC frequency of 50Hz. They can be integrated with various types of medium and high-voltage switchgear to provide reliable grounding protection.

The core function of an earthing switch is to protect both personnel and equipment:

Protecting On-site Operators: During maintenance and inspection, the earthing switch provides a reliable path to quickly dissipate any residual charges or induced voltages, thereby ensuring personnel safety.

Preventing Accidental Energization: It provides physical and visual confirmation that the relevant circuit is at zero potential before any work begins, fundamentally eliminating the risk of accidental operation.

The working principle of an earthing switch is based on a precise mechanical process. The operating mechanism applies torque to the main shaft, compressing an internal spring to store energy. Once the energy is stored, the spring releases it, causing the grounding knife to close at extremely high speed, forming a firm contact with the stationary contact. This rapid closing action ensures the reliability and safety of the grounding process, and its speed is independent of the operator’s speed.

2. Key Components of an Earthing Switch

Understanding the components of an earthing switch/grounding switch is fundamental to comprehending its function and reliability. Every component of a high-quality earthing switch is meticulously designed to work together, ensuring the system operates safely and stably under the most demanding conditions. From the core contacts to the auxiliary sensors, each part is vital for safeguarding equipment and personnel.

Indoor earthing switches in medium and high-voltage power systems feature a sophisticated internal structure, primarily composed of the following key components:

Operating Mechanism: This is the core part that drives the earthing switch’s action. It provides the torque for opening and closing, ensuring the switch can overcome resistance to perform a rapid and reliable operation. Depending on requirements, the mechanism can be a simple manual type or a motor-driven type for remote and automated control.

Insulating Base and Bracket: As the structural skeleton of the earthing switch, the insulating base and bracket are used to securely mount all core components and install them within the switchgear cabinet. The base is typically made of insulating material to provide necessary electrical isolation, while the bracket bears the mechanical stress, ensuring stability during operation.

Main Contact Assembly: This is the primary functional part for earthing, typically consisting of a movable grounding knife and a fixed stationary contact. The grounding knife rotates via the main shaft to make firm contact with the stationary contact, creating a reliable grounding path capable of carrying short-circuit currents. Its robust design is key to protecting equipment under fault conditions.

Sensor and Microswitch: To achieve precise control and interlocking, many earthing switches are equipped with sensors or micro switches. These components monitor the real-time position of the switch (open or closed) and provide status signals to the control system. This effectively prevents incorrect operations and is essential for automation and safety interlocking.

At Liyond, our JN15 earthing switch models are equipped with sensors, ensuring reliable position feedback for enhanced control and safety.

Compression Spring: The compression spring plays an energy-storing role within the operating mechanism. It is compressed during the operation and then releases its energy at a critical moment to drive the grounding knife’s rapid movement. This design ensures that the switch’s opening and closing speed is independent of the operator, thereby enhancing reliability and safety.

Insulating Cover: As an optional add-on, the insulating cover effectively increases the insulation level, providing extra protection for the earthing switch. It helps isolate live parts, further elevating the overall safety protection level of the switchgear system. In terms of safety, our earthing switch with an insulating cover has been granted a patent, and this design brings significant advantages to the product.

3. How Earthing Switches Ensure Safety: The Role of Interlocking

The interlocking mechanism is the core of how an earthing switch ensures safety. More than a simple combination of components, it’s a system that locks the operation sequence into a safe path through rigorous logical control. Without a reliable interlocking mechanism, the safety of an earthing switch would be compromised.

The switchgear interlocking mechanism is a system that uses physical or electrical methods to enforce an operational sequence, fundamentally preventing dangers caused by incorrect operation. It ensures that:

Circuit Breaker Priority: The earthing switch can only be closed after the vacuum circuit breaker has been opened and the power source has been isolated. This guarantees that the circuit is de-energized before any grounding operation occurs.

Dual Protection: The circuit breaker cannot be closed while the earthing switch is in the closed position. This physically prevents energization, providing dual protection for operators.

It is this precise interlocking design that fundamentally prevents personal injuries caused by operational errors, as well as the occurrence of devastating accidents like short circuits and arc flashes, making it the cornerstone of safe operation for modern medium and high-voltage switchgear.

4. Practical Applications and Installation of Indoor Earthing Switch

The correct application and installation of an earthing switch are crucial for ensuring the safe operation of switchgear. In practice, they are strategically installed near medium voltage disconnect switch or on both sides of a circuit breaker to provide dual grounding protection for busbars, feeder cables, or equipment during maintenance.

In common types of switchgear, earthing switches play specific roles:

In KYN 28 switchgear, the earthing switch is an integral part of the cabinet, primarily used to reliably ground the busbars or feeder cables after the main circuit breaker has been opened.

In Ring Main Units (RMU switchgear) systems, the earthing switch is a critical device for ensuring that incoming and outgoing feeder cables are at zero potential before maintenance begins.

In medium voltage gas insulated switchgear (GIS), the earthing switch is installed alongside other core components inside a sealed, gas-filled tank. Its purpose is to safely ground the internal busbars or cables after they are de-energized, thereby ensuring safety during maintenance work.

A standard safety lock-out procedure should follow these precise steps:

Open the circuit breaker to interrupt the main current.

Open the disconnector switches to physically isolate the circuit.

Close the earthing switch to ground the isolated circuit, ensuring there is no residual charge.

5. Conclusion

In summary, the indoor earthing switch is more than just a simple mechanical device; it is the cornerstone of safe operation in medium and high-voltage power systems. Its rigorous interlocking design, reliable core components, and extreme attention to detail—such as the patented insulation design—together form the first line of defense against electrical risks.

We understand that reliable grounding protection is the lifeline of safe operation in medium and high-voltage power systems. With our professional expertise and continuous technical exploration in the field of indoor earthing switches, we are able to provide you with innovative solutions that combine both safety and reliability.

If you are looking for high-performance, highly reliable indoor earthing switch products for your project and would like to receive professional, flexible switchgear solutions and technical support, we invite you to contact us at any time. Our team looks forward to partnering with you to jointly build a safe power system.