We’re all familiar with the plugs attached to the ends of appliance cords. These connectors have two or three prongs that fit into outlets having receptacles in the same configuration. The plugs are called male connectors, and the receptacles into which the plugs fit are called female connectors.
Appliance plugs and outlets provide temporary electrical connections. They can’t offer reliability in long-term applications because the prongs on any plug, and the metallic contacts inside any
receptacle, will eventually oxidize or corrode. A new male plug has shiny metal blades, but an old one has visibly tarnished blades. Similar oxidation occurs in the “slots” of a female receptacle, even
though you can’t see it.
A clip lead (pronounced “leed,” which means “wire”) comprises a short length of flexible wire, equipped at one or both ends with a simple, temporary connector. Clip leads do a poor job in
permanent installations, especially when used outdoors because corrosion occurs easily, and the connector can slip out of position. In addition, clip-lead connections can’t carry much current. Clip leads are used primarily in DC and low-frequency AC applications at low voltage and current levels.
A banana connector is a convenient single-lead connector that slips easily in and out of its
receptacle. The “business part” of a banana plug (male connector) looks something like a banana (or, if you prefer, a cucumber), as shown in Fig. 2-7. It’s like a “round peg.” Banana jacks (female
receptacles, not shown in the figure) have a cylindrical shape; they’re “round holes.” You’ll sometimes find banana jacks inside the screw terminals of low-voltage DC power supplies.
FIGURE 2-7 Banana connectors work well in low-voltage DC applications. The single contact (the plug, shown here) slides into a cylindrical receptacle (the jack, not shown here).
Warning!
Banana connectors, like clip leads, are intended for low-voltage, low-current, and short-term indoor use only. Never use these connectors with high voltages. If you do, the exposed conductors will pose an electrical shock hazard.A hermaphroditic connector is an electrical plug/jack with two or more contacts, some of them male and some of them female. Usually, hermaphroditic connectors at opposite ends of a single length of cable look identical when viewed “face-on.” However, the pins and holes have a special geometry, so you can join the two connectors in the correct way only. This “can’t-go-wrong” feature makes hermaphroditic connectors ideal for polarized circuits, such as DC power supplies, and for
multiconductor electrical control cables.
Phone plugs and jacks find extensive use in DC and low-frequency AC systems at low voltages and low-current levels. In its conventional form, the male phone plug (Fig. 2-8A) has a rod-shaped metal sleeve that serves as one contact, and a spear-shaped metal tip that serves as the other contact. A ring of hard-plastic insulation separates the sleeve and the tip. Typical diameters are 1/8 inch (3.175 millimeters) and 1/4 inch (6.35 millimeters). The female phone jack (Fig. 2-8B) has contacts that mate securely with the male plug contacts. The female contacts have built-in spring action that holds the male connector in place after insertion.
FIGURE 2-8 At A, a two-conductor phone plug. At B, a two-conductor phone jack.
Engineers originally designed the phone plug and jack for use with two-conductor cables. In recent decades, three-conductor phone plugs and jacks have become common as well. They’re used in high-fidelity stereo sound systems and in the audio circuits of multimedia computers and radio receivers.
The male plug has a sleeve broken into two parts along with a tip, and the female connector has an extra contact that touches the second sleeve when you insert the plug into the jack.
Did You Know?
The term phone comes from the original application of phone connectors: centralized community telephone switchboards that were manipulated by human operators prior to the advent of direct dialing.
Phono plugs and jacks are designed for ease of connection and disconnection of coaxial cable at low voltages and low-current levels. You can simply push the plug onto the jack, or pull it off. These connectors work in the same situations as phone plugs and jacks do, but they offer better shielding for coaxial-cable connections. Phono plugs and jacks are also known as RCA connectors, named after their original designer, the Radio Corporation of America (RCA).
Did You Know?
The term phono comes from the earliest design application of phono plugs and jacks:
interconnecting the audio components of phonographs (“record players”) in the early part of the twentieth century for music recording and reproduction.
If a cable contains more than three or four conductors, you can put a D-shell connector on either end. These connectors are available in various sizes, depending on the number of wires in the cable.
The so-called ports on a personal computer, especially the one intended for connecting the central processing unit (CPU) to an external video display, commonly employ D-shell connectors, which have the characteristic appearance shown in Fig. 2-9. The trapezoidal shell forces you to insert the plug correctly; you can’t accidentally put it in upside-down. The female socket has holes into which the pins of the male plug slide. Screws or clips secure the plug once it’s in place.
FIGURE 2-9 You can recognize a D-shell connector by its characteristic trapezoidal shape. The number of contacts can vary.
For Nerds Only
As previously mentioned, plug contacts gradually oxidize (combine with oxygen in the air), especially if exposed to the outdoors or used in a humid indoor environment. You can tell when oxidation has taken place because the metal prongs appear dark or
discolored. You can remove the oxidation, which forms in a thin layer, by rubbing the contacts with fine-grain sandpaper, emery paper, or steel wool, and then wiping the contacts off with a dry cloth. You should continue the “sanding” process until bright metal shows everywhere on the exposed parts of the contacts. If the contact prongs are too small or too closely spaced for “sanding,” you can use specially formulated contact cleaner to remove the oxidation layer. This type of cleaner can be purchased in a good hardware or electronics store, such as Radio Shack. Sometimes, a solution of table salt and vinegar will do the job, but you must be sure to rinse all of that salt off the
connectors after you use a solution like that. Otherwise, the chlorine in the salt will accelerate the corrosion process.