Screw terminal

A screw terminal is a type of electrical connection where a wire is held by the tightening of a screw.

The wire may be wrapped directly under the head of a screw, may be held by a metal plate forced against the wire by a screw, or may be held by what is, in effect, a set screw in the side of a metal tube. The wire may be directly stripped of insulation and inserted under the head of a screw or into the terminal. Otherwise, it may be either inserted first into a ferrule, which is then inserted into the terminal, or else attached to a connecting lug, which is then fixed under the screw head.

Depending on the design, a flat-blade screwdriver, a cross-blade screwdriver, hex key, Torx key, or other tool may be required to properly tighten the connection for reliable operation.

Screw terminals are used extensively in building wiring for the distribution of electricity - connecting electrical outlets, luminaires and switches to the mains, and for directly connecting major appliances such as clothes dryers and ovens drawing in excess of 15 amperes.

Screw terminals are commonly used to connect a chassis ground, such as on a record player or surge protector. Most public address systems in buildings also use them for speakers, and sometimes for other outputs and inputs. Alarm systems and building sensor and control systems have traditionally used large numbers of screw terminations.

Grounding screws are often color-coded green and, when used on consumer electronics, often have a washer with gripping "teeth", to ensure better connections.

Printed circuit board (PCB) terminal blocks are specially designed with a copper alloy pin of suitable size and length, and can be inserted into printed circuit boards for soldering in place. Some designs provide features that allow the flow of molten solder to ensure a better connection between the circuit traces of the board and the electrical equipment which is meant to be controlled or fed appropriate power.

Multiple screw terminals can be arranged in the form of a barrier strip, with a number of short metal strips separated by a raised insulated "barrier" on an insulating "block" – each strip having a pair of screws with each screw connecting to a separate conductor, one at each end of the strip. These are known as "connector strips" or "chocolate blocks" ("choc blocks") in the UK. This nickname arises from the first such connectors made in the UK by GEC, Witton in the 1950s. Moulded in brown plastic, they were said to resemble a small bar of chocolate.^{[citation needed]}