Terminal block

A screw terminal is a type of electrical connector 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.

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