Knife Switch
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A knife switch is a type of
switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type o ...
used to control the flow of
electricity Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...
in a circuit. It is composed of a
hinge A hinge is a mechanical 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, with all ...
which allows a
metal A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...
lever, or ''knife'', to be lifted from or inserted into a
slot Slot, the slot or Slots may refer to: People * Arne Slot (born 1978), Dutch football manager, former player * Gerrie Slot (born 1954), Dutch cyclist * Hanke Bruins Slot (born 1977), Dutch politician * Tonny Bruins Slot (born 1947), Dutch assoc ...
or jaw. The hinge and jaw are both fixed to an insulated base, and the knife has an insulated handle. 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. Multiple knives may be attached to a single handle and can be used to activate more than one circuit simultaneously; this is a ''multi-pole'' switch.


Current uses

Though used commonly in the past, knife switches are now rare, finding use largely in science demonstrations where the exposed mechanics of the switch make its function and state visually apparent. The knife switch is extremely simple in construction and use, but for any dangerous electrical supply its exposed metal parts present a great risk of
electric shock An electrical injury (electric injury) or electrical shock (electric shock) is damage sustained to the skin or internal organs on direct contact with an electric current. The injury depends on the Current density, density of the current, tissu ...
, and the switch is subject to
arcing An electric arc (or arc discharge) is an electrical breakdown of a gas that produces a prolonged electrical discharge. The current through a normally nonconductive medium such as air produces a plasma, which may produce visible light. An ar ...
when opened at higher
voltage Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...
s, which poses a further risk of shock or
burns Burns may refer to: Astronomy * 2708 Burns, an asteroid * Burns (crater), on Mercury People * Burns (surname), list of people and characters named Burns ** Burns (musician), Scottish record producer Places in the United States * Burns, ...
to the operator and can cause fires or explosions under certain conditions. Open knife switches were supplanted by
safety switches Safety is the state of being protected from harm or other danger. Safety can also refer to the control of recognized hazards in order to achieve an acceptable level of risk. Meanings The word 'safety' entered the English language in the 14 ...
with current-carrying contacts inside metal enclosures which can only be opened by switching off the power. In modern applications, automatic switches (such as
contactor A contactor is an electrically controlled switch used for switching an electrical power circuit. A contactor is typically controlled by a circuit which has a much lower power level than the switched circuit, such as a 24-volt coil electromagne ...
s and
relay A relay Electromechanical relay schematic showing a control coil, four pairs of normally open and one pair of normally closed contacts An automotive-style miniature relay with the dust cover taken off A relay is an electrically operated switc ...
s) and manual switches such as
circuit breaker A circuit breaker is an electrical safety device designed to protect an Electrical network, electrical circuit from damage caused by current in excess of that which the equipment can safely carry (overcurrent). Its basic function is to interr ...
s are used. These devices use snap-action mechanisms which open the switch contacts rapidly and feature arc chutes where the arcs caused by opening the switches are quenched. These devices also prevent injury due to accidental contact, as all of the current–carrying metal parts of the switch are surrounded by insulating guards.


References

* * {{engineering-stub Switches