Knife disconnect switch is a type of electrical switch that has a blade-shaped metal contact that can be inserted into or removed from a slot to make or break a circuit. It is used to manually disconnect power supply or isolate circuits for safety or maintenance purposes. Some knife disconnect switches have a lever to operate the blade, while others require manual insertion or removal. Knife disconnect switches can be single-pole or double-pole, and can have different ratings for voltage and current.
What is a knife switch used for?
A knife switch is used for controlling the flow of electricity in a circuit by manually inserting or removing a metal lever into or from a slot. It is often used as a master switch or main-disconnect for safety or maintenance purposes. Knife switches are also used in science experiments where the position of the switch may be plainly seen in demonstration.
Knife switch types
There are different types of knife switches based on their opening mechanism, number of poles and positions, and current rating. Some common types are:
- Single throw knife switch: This type has a single blade that engages with only one slot to make or break a circuit.
- Double throw knife switch: This type has a blade that is hinged between two slots and can engage with either one to switch between two circuits.
- Multiple knife switch: This type has multiple blades attached to a single handle and can be used to activate more than one circuit simultaneously.
- Out-of-the-front (OTF) knife switch: This type has a blade that comes out from the tip of the handle rather than the side. It can be either single action or double action, depending on whether the blade is retracted manually or automatically.
what is the advantage of knife disconnect switch ?
- They provide a clear visual indication of whether the circuit is on or off by the position of the blade.
- They allow convenient separation of circuits with a lever-type disconnect knife, isolating plug, or rotary contact.
- They enable user-friendly current measurement via the testing option on either side of the disconnect point.
- They ensure safe operation, as the disconnect lever is latched in the end positions.
- They have universal ratings for different regions and standards.
what is the disadvantage of knife disconnect switch ?
- They expose metal parts that present a great risk of electric shock.
- They are subject to arcing when opened at higher voltages, which poses a further risk of shock or burns to the operator and can cause fires or explosions under certain conditions.
- They are not suitable for opening a load above certain ratings, and can only be used as isolating switches.
- They are rare and outdated, and have been replaced by safer and more efficient switches such as contactors, relays or circuit breakers.
