The screw terminal is a type of electrical plug in which the wire is held by a screw tightening.
Video Screw terminal
Description
The wire can be wrapped directly under the screw head, it can be held by a metal plate that is imposed on the wire with a screw, or it can be held by what is actually a set screw on the side of the metal tube. The wire can be immediately removed from the insulation and inserted under the screw head or to the terminal. If not, it can be inserted first into the ferrule, which is then inserted into the terminal, or attached to the connecting lug. which is then fixed under the screw head.
Depending on the design, a minus screwdriver, a crosslink, a hex key, a Torx key, or other device may be required to tighten the connection properly in order to operate properly.
Maps Screw terminal
Apps
Screw terminals are widely used in building cables for power distribution - connecting electrical outlets, luminaires and switches to electricity, and for directly connecting main equipment such as clothes dryers and ovens drawing over 15 amperes.
Screw terminals are commonly used to connect the chassis ground, such as on a recording player or surge protector. Most public address systems in the building also use it for speakers, and sometimes for output and other inputs. Alarm systems and building sensors and control systems have traditionally used a large number of screw terminations.
Grounding screws are often colored green and, when used on electronic devices, often have a geared washing machine.
Printed board terminal blocks (PCBs) are specially designed with copper alloy pins of appropriate size and length and can be inserted into printed circuit boards to be soldered to allow electrical signals and current to flow to and from PCBs and electrical equipment. Some designs provide features that allow the flow of liquid solder to survive better connections between circuit board traces and electrical equipment intended to be controlled or powered accordingly.
Multiway version
Some screw terminals can be arranged in the form of a strip baffle (as illustrated at the top right), with a number of short metal strips separated by isolated "barriers" on isolated "blocks" - each strip has a pair of screws with each the screw that connects to a separate conductor, one at each end of the strip. This is known as a connector strip or brown block ("choc block") in the UK. This nickname came from the first connector made in the UK by GEC, Witton in the 1950s. Formed in brown plastic they are said to resemble a small chocolate bar.
A similar arrangement is common with the screw terminal attached, in which the metal tubes are loosely encased in an insulating block with a set of screws at each end of each tube for holding and thereby connecting a conductor. It is often used to connect lights and is displayed on the right.
Alternatively, the terminal can also be set as terminal strip or terminal block , with multiple screws along (usually) two long strips. This creates a bus bar for power distribution, and may also include a parent input connector, usually a binding post or banana connector.
Installation
The installation of screw joints requires some maintenance in progress to ensure proper insulation exposure, containment of all strands of wire, and adequate screw tightening. If the diameter of the wire is small in relation to the size of the screw, the wire may be cut through over-tightening screws. This is less likely to occur when the wire is clamped between two plates by screw action. Since the wire strand can not be contained by the screw head in the base screw terminal, the wounded cable can be crimped into the ferrule to prevent the terminal connector; this partially offset the economics of "naked" wire termination.
While cables may be wrinkled, they should not be heavily tinned with solder before installation in screw terminals, because the soft metal will flow cold, resulting in loose connections and possible fire hazards. Screw connections are sometimes loose if not tight enough to work at a time. Verifying sufficient torque torque requires calibrated installation equipment and proper training. In the UK, all screw connectors on electrical installations must still be accessible for service, for this reason.
Advantages and disadvantages
Screw terminals are low cost when compared to other types of connectors, and can easily be designed to be products for circuits carrying currents from ampere fractions up to several hundred amperes at low to moderate frequencies. Terminals can easily be reused in the field, allowing for replacement of cables or equipment, generally with standard hand tools. Screw terminals usually avoid the requirement for special mating connectors to be applied to the end of the cable.
When tightened properly, the connections are physically and electrically secure as they firmly contact most wires. Terminals are relatively cheaper than other types of connectors, and screw terminals can be easily integrated into the design of building wiring devices (such as sockets, switches, or lamp stands).
Losses include the time it takes to disarm the wire and, at the base terminal, wrap it around the screw head properly, because it is important that any wire installed under the screw head will "wound" in the right direction (usually clockwise,) so that the conductor not forced out when the screws are tightened. This procedure is more time consuming than using plug-in connectors - thus making screw connections unusual for portable equipment, where cables are repeatedly connected and disconnected.
However, with this type of screw terminal clamp type it is reduced, since it only needs to insert the stripped wire between the terminal and rear clamp plate and tighten the joint, using a screw to clamp the wire between the terminals and clamp the plate, without needing to wrap it properly around the screw head.
The screw mechanism limits the minimum physical size of the terminal, making screw terminals less useful where multiple connections are required.
It is difficult to automate multiple terminations with a screw connection.
Vibration or corrosion can cause screw connections to deteriorate over time.
The use of screw terminals "brown blocks" in building cable installations has dropped sharply for the sake of crimp type connectors, push and twist that are not easily detachable and easier to install. In the UK chocolate block is no longer approved for inaccessible connections for inspection (eg Under the floor).
See also
- Chocbox
- Wire nuts
- Euroblock
References
Source of the article : Wikipedia
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