A knife switch is a type of switch

Switch

In electronics, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another....

 used to control the flow of electricity

Electricity

Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

 in a circuit. It is composed of a hinge

Hinge

A hinge is a type of bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation. Hinges may be made of flexible material or of moving components...

 which allows a metal

Metal

A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

 lever, or knife

Knife

A knife is a cutting tool with an exposed cutting edge or blade, hand-held or otherwise, with or without a handle. Knives were used at least two-and-a-half million years ago, as evidenced by the Oldowan tools...

, to be lifted from or inserted into a slot

Slot

Slot may refer to:* A narrow opening through which an object can pass, for example in a:** Vending machine slot** Slot machine, a type of casino game* Slot, a space for a container on a ship, usually expressed as a 20' or 40' slot Slot may refer to:* A narrow opening through which an object can...

 or jaw. The hinge and jaw are both fixed to an insulated

Electrical insulation

thumb|250px|[[Coaxial Cable]] with dielectric insulator supporting a central coreThis article refers to electrical insulation. For insulation of heat, see Thermal insulation...

 base, and the knife has an insulated handle to grip at one end. Current flows through the switch when the knife is pushed into the jaw.
Knife switches can take several forms, including single throw, in which the "knife" engages with only a single slot, and double throw, in which the knife hinge is placed between two slots and can engage with either one. Also, multiple knives may be attached to a single handle and can be used to activate more than one circuit simultaneously.

Current uses

Though once common in the early days of electricity, knife switches are now rare, finding use largely in science experiments where the position of the switch may be plainly seen in demonstration. The knife switch is extremely simple in construction and use, but its exposed metal parts present a great risk of electrocution

Electric shock

Electric Shock of a body with any source of electricity that causes a sufficient current through the skin, muscles or hair. Typically, the expression is used to denote an unwanted exposure to electricity, hence the effects are considered undesirable....

, and the switch is subject to arcing

Electric arc

An electric arc is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air. A synonym is arc discharge. An arc discharge is characterized by a lower voltage than a glow discharge, and relies on...

 when opened at higher voltages

Voltage

Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

, which poses a further risk of shock or burns

Burn (injury)

A burn is a type of injury to flesh caused by heat, electricity, chemicals, light, radiation or friction. Most burns affect only the skin . Rarely, deeper tissues, such as muscle, bone, and blood vessels can also be injured...

 to the operator and can cause fires or explosions under certain conditions.

Open knife switches were supplanted by safety switches

Isolator switch

In electrical engineering, a disconnector or isolator switch is used to make sure that an electrical circuit can be completely de-energised for service or maintenance. Such switches are often found in electrical distribution and industrial applications where machinery must have its source of...

 with current carrying contacts inside a metal enclosure which can only be opened by switching off the power. In modern applications, automatic switches (such as contactors

Contactor

A contactor is an electrically controlled switch used for switching a power circuit, similar to a relay except with higher current ratings. A contactor is controlled by a circuit which has a much lower power level than the switched circuit....

 or relays

Relay

A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal , or where several circuits must be controlled...

), and manual switches such as circuit breakers

Circuit breaker

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow...

 are used. These devices use a snap action mechanism which opens the switch contacts rapidly, and feature an arc chute where the arc caused by opening the switch is quenched. These devices also prevent injury due to accidental contact, as all of the current carrying metal parts of the switch are hidden within or surrounded by insulating guards.