The Complete Guide to DC Isolating Switch

Isolation is essential in modern electrical equipment, from industrial automation systems to medical devices and solar inverters. They help prevent cross-contamination of hazardous voltages within an electrical system in case there is any malfunction or breakdown.

The DC switch is the most popular type of isolator switch, controlling two separate circuits with a single pole. Other popular options include three-pole (DP) isolators and fused switch disconnectors.

What is a DC Isolating Switch?

A DC isolator switch allows power to an electrical circuit to be turned on or off by creating or breaking an electrical connection. Its purpose is to safely isolate your system from its source of power, such as batteries or solar panels, while also enabling manual disconnection of the circuit for safety reasons.

DC isolating switches can be either built-in or external, depending on their application. For built-in switches, the number of Multi-Phase Power Tracking (MPPT) poles of an inverter determines its poles: single MPPT for common string inverters with rated power between 1kW and 30kW; a dual or small amount of triple MPPT for inverters with higher rated powers over 30kW.

Types of DC Isolating Switch

DC Isolating Switches allow maintenance work to be performed without interrupting circuits, helping protect against potential fires or electrical short circuits and extending the life of the equipment.

When selecting a switch, there are various types available to meet your requirements. Make sure the one you select has been certified according to an established standard.

• Single Pole Isolator

Isolating switches are used by electricians and maintenance personnel to guarantee an electrical circuit or equipment is safely isolated for safe maintenance, servicing, modification, or repair. They can be found in residential properties, electrical substations, and vehicle battery systems.

These come in a range of models designed for different purposes. Some run on alternating current (AC), while others run off direct current (DC).

• Double Pole Isolator

Double pole isolator switches allow two poles to be connected or disconnected simultaneously. They’re commonly used in medical applications, as well as commercial ones.

Contrary to a single pole isolator, this switch only powers down the neutral leg of the circuit. This ensures that no damage occurs to equipment connected to it.

• Line Side Isolator

An electrical isolator is a manual mechanical switch that isolates part of the power supply. Also referred to as a disconnector switch, this device operates only when there are no loads present.

Isolators are commonly utilized in electrical power distribution and substations to protect against power surges and other electrical hazards.

• Bus Side Isolator

The Bus Side Isolator is a common DC Isolating Switch located between the circuit breaker and the main bus of your power system.

The isolator is designed to operate when there is no load on the circuit and is typically installed along with a circuit breaker in an electrical substation.

• Transfer Bus Isolator

In a main and transfer bus system, each feeder line is directly connected to an isolator on the second bus called the transfer bus. This isolator in between is typically referred to as a bypass isolator.

A main and transfer bus system is an alternative to the double bus. In this setup, equipment connected to a bay is fed from one bus and transferred to another when necessary without disengaging its load.

Applications of DC Isolating Switch

Disconnector switches are used in electrical engineering to guarantee an electrical circuit is de-energized for service or maintenance. They may be operated manually or with motor assistance, and they may also be coupled with an earthing switch to ground the portion that has been isolated from the system for additional safety.

In order to install a photovoltaic system, you need an effective means of isolating the power source. A DC isolation switch can come in handy here; it allows you to completely disconnect your solar panels during maintenance or repair work.

Before anything else, it’s important to understand that a DC isolator switch is different from a circuit breaker. While the latter can protect your system from overloads and short circuits, it doesn’t offer arc-suppression and shock protection features like those found in a DC isolation switch.

Working Principles of DC Isolating Switch

A DC isolator switch is used to safely isolate DC power sources such as photovoltaic systems and battery storage systems. It usually consists of two or more contractors that are activated by turning a handle or rotary switch and can be mounted indoors or outdoors.

When the handle is turned, a mechanical switch opens, creating an arc voltage that supplies current to an electronic switching element. After extinguishing, however, the arc vanishes, and the switch closes securely, cutting off the circuit and isolating it from any further external influences.

The switch can also be equipped with a lockout-tag out feature to prevent inadvertent operation. This is especially crucial in high voltage or complex systems, where it safeguards against accidental activation of the switch.

Electrical isolators come in a range of types, each with its own specific operating requirements and features. Which one is best suited to your application depends on how it will be operated and where you reside.

Advantages and Disadvantages of DC Isolating Switches

Isolating switches are essential components in applications requiring electrical separation between input and output voltages. Unfortunately, these isolated components come with design tradeoffs that engineers should be aware of.

• Cost

DC Isolating Switches are an economical and practical way to isolate power, particularly in photovoltaic systems and battery storage applications. They usually consist of a box-like structure mounted on walls or panels with either a handle or rotary switch for easy operation.

The cost of a switch varies based on its size and features, though generally speaking, they are cheaper than circuit breakers.

• Safety

An isolator switch may be a safer and more reliable alternative to circuit breakers in certain applications. These switches block current flow to the electrical system and can be safely operated by an experienced technician.

Isolators can also be employed in situations that pose a potential risk of electric shocks. This allows individuals to work on the affected section of the electrical system without fear of electrocution.

• Reliability

DC Isolating Switches are essential safety elements in the operation of PV power plants. Their reliability and stability are directly tied to that a plant’s safety, which in turn ensures stable power generation and profitability.

DC isolators are superior to other products because they provide a positively trip-free mechanism that remains independent of external influences, regardless of how slowly or quickly a switch actuator is turned on or off. 

• Installation

A DC isolating switch is the safe and secure way to manually disconnect your solar panels from your system for maintenance or repair work. This can be done safely by a technician without the risk of contact with energized components, making it safer than relying on circuit breakers.

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