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Knife switch

technology Maturity 11-13 Next article →

A knife switch is a tool used to control electricity. It manages the flow of power in an electrical circuit.

Open knife switch
Open knife switch

This device is very simple to build and use. It helps people turn power on or off easily. You can see how the switch works just by looking at it. This makes it a great tool for showing science ideas.

Electrical Machinery 1917 - knife switch
Electrical Machinery 1917 - knife switch

This switch works using a metal lever called a knife. The knife is attached to a hinge. This hinge sits on an insulated base. The base keeps the electricity from moving where it should not go. The knife also has an insulated handle for safety.

IEEE 315 Contacts, Switches, Contactors, and Relays Symbols (52)
IEEE 315 Contacts, Switches, Contactors, and Relays Symbols (52)

To start the power, you push the knife into a slot or jaw. This completes the path for the current. To stop the power, you lift the knife out of the slot.

There are different ways to set up these switches. A single-throw switch has only one slot for the knife. A double-throw switch has two slots. In that case, the hinge sits between the two slots. The knife can go into either one of them.

DPDT knife switch in closed position
DPDT knife switch in closed position

You can also have a multi-pole switch. This type has many knives on one single handle. This lets one person start many circuits at the same time.

These switches were used very often in the past. Now, you will find them much less often. They are mostly used in science demonstrations today. Teachers like them because the moving parts are easy to see. However, they can be quite dangerous to use. The metal parts are out in the open. This creates a risk of electric shock for the person using it.

Electrical Machinery 1917 - knife switch
Electrical Machinery 1917 - knife switch

High voltage can cause something called arcing. This happens when sparks jump when the switch opens. Arcing can cause burns or even start fires. Because of this, people now use safer switches. Modern switches keep the metal parts inside metal enclosures. They use snap-action parts to move very quickly. These new tools use guards to prevent accidental contact. This keeps the electricity tucked away safely.

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🖼️ Images & Media (4)
File:Open knife switch.jpg
Open knife switch.jpg
File:IEEE 315 Contacts, Switches, Contactors, and Relays Symbols (52).svg
IEEE 315 Contacts, Switches, Contactors,...
File:Electrical Machinery 1917 - knife switch.jpg
Electrical Machinery 1917 - knife switch.jpg
File:DPDT knife switch in closed position.jpg
DPDT knife switch in closed position.jpg
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