A screw terminal is a type of electrical connector

Electrical connector

An electrical connector is an electro-mechanical device for joining electrical circuits as an interface using a mechanical assembly. The connection may be temporary, as for portable equipment, require a tool for assembly and removal, or serve as a permanent electrical joint between two wires or...

 where a wire

Wire

A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...

 is clamp

Clamp (tool)

A clamp is a fastening device to hold or secure objects tightly together to prevent movement or separation through the application of inward pressure...

ed down to 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...

 by a screw

Screw

A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...

.
The wire is sometimes just stripped of electrical insulation

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...

 at the end, and is bent in a U or J shape to fit around the shaft of the screw.
Alternatively, a lug can be crimped

Crimp (joining)

Crimping is joining two pieces of metal or other malleable material by deforming one or both of them to hold the other. The bend or deformity is called the crimp.- Uses :...

 onto the end of the wire to protect it. Setscrews are also used, as in a luster terminal or lustre terminal, but lugs will not fit into them. For both lugs and bare wire, the screw is tightened for a secure connection.

Description and usage

Screw terminals are commonly used to connect a chassis ground, such as on a record player or surge protector

Surge protector

A surge protector is an appliance designed to protect electrical devices from voltage spikes. A surge protector attempts to limit the voltage supplied to an electric device by either blocking or by shorting to ground any unwanted voltages above a safe threshold...

. Most public address

Public address

A public address system is an electronic amplification system with a mixer, amplifier and loudspeakers, used to reinforce a sound source, e.g., a person giving a speech, a DJ playing prerecorded music, and distributing the sound throughout a venue or building.Simple PA systems are often used in...

 systems in buildings also use them for speakers

Loudspeaker

A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...

, and sometimes for other outputs and inputs. They are also used extensively in wiring for 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...

, for connecting electrical outlets and 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....

es to the mains

Mains electricity

Mains is the general-purpose alternating current electric power supply. In the US, electric power is referred to by several names including household power, household electricity, powerline, domestic power, wall power, line power, AC power, city power, street power, and grid power...

, and for connecting major appliance

Major appliance

A major appliance, or domestic appliance, is usually defined as a large machine which accomplishes some routine housekeeping task, which includes purposes such as cooking, or food preservation, whether in a household, institutional, commercial or industrial setting...

s like clothes dryer

Clothes dryer

A clothes dryer or tumble dryer is a household appliance that is used to remove moisture from a load of clothing and other textiles, generally shortly after they are cleaned in a washing machine....

s and oven

Oven

An oven is a thermally insulated chamber used for the heating, baking or drying of a substance. It is most commonly used for cooking. Kilns, and furnaces are special-purpose ovens...

s to the particular plug installed in a home, or directly hard-wiring to the house, as required by local electrical code

Electrical code

An electrical code is a set of regulations for electrical wiring. The intention of an electrical code is to provide standards to ensure electrical wiring systems that are safe and unlikely to produce either electric shock or fires. Electrical codes are usually devised by national or international...

s in the US. For reliability reasons, screw terminals for earth ground connections are preferred on most USA-style outlets, even for those that otherwise have "rear-wire" push-in connections, despite the difficulty of bending heavy-gauge

Wire gauge

Wire gauge is a measurement of how large a wire is, either in diameter or cross sectional area. This determines the amount of electric current a wire can safely carry, as well as its electrical resistance and weight per unit of length...

 solid copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 around a screw with pliers

Pliers

Pliers are a hand tool used to hold objects firmly, for bending, or physical compression. Generally, pliers consist of a pair of metal first-class levers joined at a fulcrum positioned closer to one end of the levers, creating short jaws on one side of the fulcrum, and longer handles on the other...

. Grounding screws are often marked green, and when used on consumer electronics

Consumer electronics

Consumer electronics are electronic equipment intended for everyday use, most often in entertainment, communications and office productivity. Radio broadcasting in the early 20th century brought the first major consumer product, the broadcast receiver...

 often have a washer

Washer (hardware)

A washer is a thin plate with a hole that is normally used to distribute the load of a threaded fastener, such as a screw or nut. Other uses are as a spacer, spring , wear pad, preload indicating device, locking device, and to reduce vibration...

 with gripping "teeth".

Multiway version

Multiple screw terminals can be arranged as a barrier strip, with each short metal strip having a pair of screws. This is used for connecting two different components, one on each side of the pairs. This arrangement is common in luster terminals, as pictured at left. These are known as connector strips or chocolate blocks in the UK. Conversely, terminals can also be arranged as a terminal strip or terminal block, with several screws along (typically) two long strips. This creates a bus bar for power distribution, and so may also include a master input connector, usually binding post

Binding post

A binding post is a connector commonly used on electronic test equipment to terminate a single wire or test lead. They are also found on loudspeakers and audio amplifiers as well as other electrical equipment....

s and/or banana connector

Banana connector

A banana connector is a single-wire electrical connector used for joining wires to equipment. The term 4 mm connector is also used, especially in Europe, although not all banana connectors will mate with 4mm parts...

s.

Advantages and disadvantages

One advantage of screw terminals is that no connectors are used, thus no compatibility

Compatibility

Compatibility may refer to:* Astrological compatibility* Compatibilism – a philosophical position* Compatibility * Compatibility * Compatibility * Electromagnetic compatibility* Interpersonal compatibility-Computing:...

 problems with mismatched sizes or shapes. Additionally, the connections are very secure, both physically and electrically, because they firmly contact a large section of wire. This is also a disadvantage however, because it can take a few minutes to secure or undo a set of connections that could otherwise be simply plugged or unplugged. Another disadvantage is that their use with wire too thin is liable to partly cut through the wire.

Screw connectors sometimes come loose over time if not done up tightly enough at fitting time. In the UK all screw connectors on fixed mains installations are required to be accessible for servicing for this reason.

Overtightening can cut most of the way through wires.

An alternative in some countries is to use wire nut

Wire nut

Twist-on wire connectors are used to fasten two or more electrical conductors together. They are a type of electrical connector.Twist-on wire connectors are also known as wire nuts or cone or thimble connectors. Marrette or Marr connectors are two other trade names for such connectors...

s, usually done where there is no chassis

Chassis

A chassis consists of an internal framework that supports a man-made object. It is analogous to an animal's skeleton. An example of a chassis is the underpart of a motor vehicle, consisting of the frame with the wheels and machinery.- Vehicles :In the case of vehicles, the term chassis means the...

involved.