Banana connector
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A banana connector (commonly banana plug for the male, banana jack for the female) is a single-wire (one conductor) electrical connector, widely used in science laboratories for temporarily joining wires to equipment. It consists of a cylindrical metal pin about 25 mm (one inch) long, with a diameter of 4 mm, which can be inserted into a matching 4 mm socket to make an electrical contact. While it is also called a 4mm connector (likewise 4mm plug or 4mm jack, as above), there are also other sizes used for other applications. The pin has one or more lengthwise springs that bulge outwards slightly. These press against the sides of the socket, improving the electrical contact and preventing the pin from falling out. The curved profile of these springs is probably the origin of the name "banana plug". The other end of the plug has a hole that accepts a length of flexible insulated equipment wire, which is either screwed or soldered into place. An insulating plastic cover is usually fitted over this end.
The wide end of a 4 mm plug often has a 4 mm hole drilled in it, either transversely or axially, to accept the pin of another 4 mm plug. This type is called a stackable 4 mm plug.
4 mm plugs are frequently used to terminate patch cords for electronics laboratory equipment. They are also sometimes used as the plugs on the cables connecting the amplifier to the loudspeakers in a hi-fi sound system.
Besides plugging into specific banana jacks, banana plugs may plug into five-way or universal binding posts.
[edit] Miniature connectors
A miniaturized version of the banana connector was also produced. About 1/3 the size of the standard connector, these were useful in high-density applications but never achieved the same sort of popularity as the larger banana connectors. They are substantially more fragile than the larger connectors.
[edit] Electrical safety
An exposed banana plug can obviously present electrical hazards if the wire to which it is attached is energized. The hazards include electric shock, electrocution, burns from accidental short circuits, and damage to the attached equipment. Where electrical safety is an issue, due to the presence of higher voltages and/or currents, various kinds of protected plugs and sockets are available. These have sliding covers on plugs and/or other devices to protect the user from accidental contact with live conductors, but are still largely compatible with the original design.
A typical design is now required on digital voltmeter test leads. In this design, the metal banana plug is entirely sheathed in plastic and presses into a deep recess in the DVM. Alternatively, the DVM has the male part of the banana plug and it is deeply recessed ; the test lead contains a sheathed banana jack.
| Audio and video connectors |
|---|
| Single conductor: Binding post | Banana plug | Fahnestock clip |
| Audio: RCA | Jack plug | XLR | DIN / Mini-DIN | BNC | DB25 | Speakon | TosLink |
| Video: DVI / Mini-DVI / UDI | RCA | VGA / Mini-VGA | DFP | P&D | BNC | DIN / Mini-DIN | 13W3 | D4 | DisplayPort |
| Multi: ADC | HDMI | TRS | SCART | F | Belling-Lee | DisplayPort |
