Electrical Knife Switch

1.What is a Electrical Knife Switch ?

Knife switches, also known as disconnect switches, are simple and widely used low-voltage manual electrical components.

Their core function in low-voltage power distribution systems is power isolation, as well as connecting and disconnecting load circuits within the rated current range. They are indispensable basic components in power distribution and control circuits.

Technical advantages: Simple mechanical structure and economical manufacturing cost; convenient manual operation, and a clearly visible physical disconnection point in the open position, allowing for visual confirmation of power isolation and ensuring maintenance safety.

Technical limitations: Limited short-circuit breaking capacity, and products without arc extinguishing chambers have poor arc extinguishing performance; they lack automatic control functions, and the characteristics of their mechanical contacts make them unsuitable for high-frequency switching applications.

2.What are the Different Types of Electrical Knife Switches ?

Knife switches come in many models and can be classified according to their use and structure.

Ordinary open-type knife switches do not have a dedicated arc extinguishing structure and are only suitable for no-load switching or small current loads, mainly serving as power isolation.

These switches include the HD (Single Pole Single Throw knife switch) series and the HS (Single Pole Double Throw knife switch) series.

Knife switches equipped with arc extinguishing covers can extinguish the arc generated during switching, allowing them to directly switch loads within the rated current without the need for additional arc extinguishing components.

These switches include the HR (fuse-type knife switch) series and the HK (porcelain base and plastic cover knife switch) series.

Enclosed knife switches are completely sealed within a metal casing. These switches have a high protection rating, better arc extinguishing performance than ordinary open-type switches, and are safer to operate.

These switches include the HH (enclosed load switch) series.

3.How Does a Electrical Knife Switch Work?

The working principle of a knife switch is based on manually moving a handle to either connect or disconnect the contacts inside, thereby controlling the opening and closing of the circuit.

Models with arc suppressors also include an additional “arc extinguishing” step, making them safer to use.

Ordinary open-type knife switches: Flipping the handle to the “on” position connects the contacts, allowing electricity to flow; flipping the handle to the “off” position separates the contacts, interrupting the power. It’s easy to see whether the power is on or off at a glance.

Knife switches with arc suppressors: When the circuit is broken, an electric spark, or arc, is generated at the moment the contacts separate. This can easily burn the contacts. Fortunately, the arc suppressor absorbs the arc, using internal grids to break the arc into smaller segments, quickly extinguishing it and protecting the switch from damage.

Double-throw HS series knife switches: These have two sets of fixed contacts, and the moving contact can switch between the two sets, allowing for switching between two power sources, such as mains power and backup power.

However, when switching, one circuit must be disconnected before connecting the other, otherwise, connecting both power sources simultaneously will cause problems.

HR series knife-fuse switches: These combine a knife switch and a fuse into one unit. In normal use, they function like a regular knife switch, manually controlling the power on and off; however, if the current in the circuit is too high or a short circuit occurs, the internal fuse will automatically melt, interrupting the power without manual intervention, providing protection.

4.What are the Typical Applications of Knife Switches?

A electrical knife switch  is a simple and easy-to-use low-voltage electrical switch, primarily used for two things: disconnecting power for safety and occasionally switching small electrical appliances.

Its application depends on the current and the specific situation.

“Safety Disconnect” in Distribution Cabinets

This is its main use. We can see it installed in front of circuit breakers and fuses in factory distribution cabinets and building electrical distribution boxes.

When repairing circuits or replacing electrical appliances, disconnecting it clearly shows that “the power is off,” preventing accidental electric shocks and ensuring safety.

“Simple Switch” for Low-Power Appliances

For low-power appliances that are not frequently switched on and off, a knife switch can directly control them:
It can be used as the main switch for lighting in old houses and for temporary lighting on construction sites.

For low-power motors like small exhaust fans and small water pumps, as long as they are not frequently started and stopped, it can be used to control the power supply.

Pure heating appliances like electric heaters and small electric stoves can also be directly switched on and off with it.

Adding Fuses for Short-Circuit Protection

Knife switches with fuses can both disconnect the power and prevent short circuits from causing fires.

They are suitable for control boxes of small machines, water pump circuits for irrigation in rural areas, and equipment lines in small processing plants, eliminating the need for additional protection devices and saving trouble.

“Durable Switch” for Construction Sites and Mines

Knife switches have a robust structure, are resistant to bumps and impacts, and can withstand harsh environments:
For temporary power connections on construction sites and for small outdoor equipment, an outdoor model with a rainproof casing can be used.

In dusty and somewhat vibrating environments like mines and metallurgical plants, heavy-duty knife switches can serve as isolation switches for auxiliary circuits, proving very durable.

Important Note: Do not use it for frequently switched appliances or for high-power equipment and motors that are frequently started and stopped.

Also, it does not provide overload protection and cannot replace circuit breakers; otherwise, the arc may not be extinguished, potentially burning equipment or even causing fires.