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378:, resulting in a loose connection and possible fire hazard. Screw connectors sometimes come loose if not done up tightly enough at fitting time. Verifying adequate tightening torque requires calibrated installation tools and proper training. In the UK, all screw connectors on fixed mains installations are required to be accessible for servicing, for this reason.
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However, with the clamping plate type of screw terminal this time is reduced, since it is necessary only to insert the stripped wire between the terminal and the rear clamping plate then tighten the connection, using the screw to clamp the wire between the terminal and the clamping plate, without any
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Screw terminals are low in cost when compared to other types of connectors, and can be readily designed into products for circuits carrying currents of from a fraction of an ampere up to several hundred amperes at low to moderate frequencies. The terminals easily can be re-used in the field, allowing
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Assembly of a screw connection requires some care in workmanship to ensure proper removal of insulation, containment of all wire strands, and the adequate tightening of the screw. If the wire diameter is small in relation to the size of the screw, the wire may be cut through by the over-tightening of
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When properly tightened, the connections are physically and electrically secure because they firmly contact a large section of wire. The terminals are relatively low cost compared with other types of connector, and a screw terminal can easily be integrated into the design of a building wiring device
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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
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Disadvantages include the time taken to strip a wire and, in basic terminals, properly wrap it around a screw head, since it is essential that any wire installed under a screw head be "wound" in the correct direction (usually clockwise,) so that the conductors are not forced outwards when the screw
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The use of screw terminal "chocolate blocks" in building wiring installations has sharply declined in favour of crimp, push, and twist type connectors which are and easier to fit, and less vulnerable to working loose. In the UK, chocolate blocks are no longer approved for connections that are not
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Two types of screw terminals showing a significant development in design. Basic, with the wires held between the screw heads and the terminals (left) and with the wires held, reversely, between the metal clamping plates and the rear of the terminals
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the screw. This is less likely to occur when a wire is clamped between two plates by the action of a screw. Since wire strands may not be contained by the screw head in a basic screw terminal, stranded wires may be first crimped into a
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is tightened. This procedure is more time-consuming than using a plug-in connector, thus making screw connections uncommon for portable equipment, where wires are repeatedly connected and disconnected.
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for the replacement of wires or equipment, generally with standard hand tools. Screw terminals usually avoid the requirement for a specialized mating connector to be applied to the ends of wires.
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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
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Screw terminals, as individual connectors to a board at left, as a barrier strip with setscrews at top, and as a barrier strip with attached spade and loop lugs at bottom.
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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
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The screw mechanism limits the minimum physical size of a terminal, making screw terminals less useful where large numbers of connections are required.
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A similar arrangement is common with paired screw terminals, where metal tubes are loosely encased in an insulating block with a
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to prevent the bridging of terminals; this partly offsets the simplicity and economy of a "bare" wire termination.
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circuit traces of the board and the electrical equipment which is meant to be controlled or fed appropriate power.
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and building sensor and control systems have traditionally used large numbers of screw terminations.
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at each end of each tube to clamp and thus connect a conductor. These are often used to connect
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key, or other tool may be required to properly tighten the connection for reliable operation.
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It is difficult to automate multiple terminations with screw connections.
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Two paired screw terminals, typically used for connecting ceiling-mounted
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prior to installation in a screw terminal, since the soft metal will
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While wires may be crimped, they should not be heavily tinned with
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Multiple screw terminals can be arranged in the form of a
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can cause a screw connection to deteriorate over time.
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with gripping "teeth", to ensure better connections.
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253:Screw terminals are commonly used to connect a
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64:. Unsourced material may be challenged and
128:Learn how and when to remove this message
214:Screw terminals are used extensively in
269:systems in buildings also use them for
183:Depending on the design, a flat-blade
27:Device for electrical wire connection
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62:adding citations to reliable sources
250:drawing in excess of 15 amperes.
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160:is held by the tightening of a
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382:Advantages and disadvantages
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468:Electrical connectors
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58:improve this article
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16:(Redirected from
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56:Please help
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282:color-coded
220:electricity
185:screwdriver
168:Description
118:August 2013
454:References
228:luminaires
88:newspapers
448:Euroblock
422:corrosion
418:Vibration
376:cold flow
321:set screw
174:set screw
45:does not
462:Category
443:Wire nut
432:See also
391:(right).
271:speakers
265:. Most
242:such as
232:switches
156:where a
438:Chocbox
365:ferrule
340:bus bar
234:to the
189:hex key
178:ferrule
102:scholar
66:removed
51:sources
372:solder
290:washer
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248:ovens
236:mains
162:screw
109:JSTOR
95:books
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193:Torx
158:wire
81:news
49:any
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