A banana connector (commonly banana plug for the male, banana jack for the female) is a single-
wire(one conductor) electrical connectorused for joining wires to equipment. The plugs are frequently used to terminate patch cords for electronic test equipment. They are also used as the plugs on the cables connecting the amplifierto the loudspeakers in a hi-fi sound system.
The plug was invented in 1924 by Richard Hirschmann (former Richard
HirschmannGmbH & Co.).
The plug consists of a cylindrical metal pin about 25 mm (one
inch) long, with a diameterof 4 mm, which can be inserted into a matching 4 mm socket to make an electrical contact. While it is also called a 4 mm connector (likewise 4 mm plug or 4 mm 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 plasticcover 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.
For high voltage use, a special sheathed version of the banana plug and socket is used. This version has an insulating sheath around both the male and female connectors to avoid accidental contact. The sheathed male plug will not work with an unsheathed female socket, but an unsheathed male plug will fit a sheathed female socket.
The plastic housing is often extended to contain two banana plugs, allowing simultaneous connection of a signal line and a ground (earth) line; see the photo. The housing may allow the connection of individual wires, a permanently attached
coaxial cableproviding both signal and ground, or a coaxial connector such as the BNC connectorshown in the photo. By convention, multiple full-sized banana connectors are spaced on ¾ inch centers.
Individual banana plugs and jacks are commonly color-coded red and black but are available in a wide variety of colors. Dual banana plugs are usually black with some physical feature such as a molded ridge marked "Gnd" indicating the relative polarity of the two plugs.
Besides plugging into specific banana jacks, banana plugs may plug into "five-way" or "universal"
binding posts on audio equipment.
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. Multiple miniature banana connectors are usually spaced on ½ inch centers.
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.
In parts of Europe where the standard mains power connector is the
Schukoconnector, it can be difficult to purchase US-style "double banana" plugs. The standard US pin spacing of 3/4 inch is very close to the Schuko spacing of 19 mm. It is easy to insert a double banana into a Schuko power outlet, leading to a risk of electrical shock.
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