Defensive design is the practice of planning for contingencies in the design stage of a project or undertaking. Essentially, it is the practice of anticipating all possible ways that an end-user could misuse a device, and designing the device so as to make such misuse impossible, or to minimize the negative consequences. For example, if it is important that a plug is inserted into a socket in a particular orientation, the socket and plug should be designed so that it is physically impossible to insert the plug incorrectly. Power sockets are often keyed in such a manner, to prevent the transposition of live and neutral. They are also recessed in the wall in a way that makes it impossible to touch connectors once they become live.
Defensive design in software engineering is called defensive programming. Murphy's law is a well-known statement of the need for defensive design, and also of its ultimate limitations.
Implementation decisions and software design approaches can make software safer and catch user errors. Code that implements this is termed a sanity check.
Many electrical connectors apply this principle by being asymmetric. Alternatively, USB-C plugs are mechanically but not electrically symmetric, but achieve an illusion of symmetry resulting from how devices respond to the cable, and hence can be plugged in either of two ways. Accompanying circuitry makes the plugs and cables behave as though they are symmetric.
SCART is a French-originated standard and associated 21-pin connector for connecting audio-visual (AV) equipment. The name SCART comes from Syndicat des Constructeurs d'Appareils Radiorécepteurs et Téléviseurs, "Radio and Television Receiver Manufacturers' Association", the French organisation that created the connector in the mid-1970s. The related European standard EN 50049 was refined and published in 1978 by CENELEC, calling it péritelevision, but it is commonly called by the abbreviation péritel in French.
Components of an electrical circuit are electrically connected if an electric current can run between them through an electrical conductor. An electrical connector is an electromechanical device used to create an electrical connection between parts of an electrical circuit, or between different electrical circuits, thereby joining them into a larger circuit.
A phone connector is a family of cylindrically-shaped electrical connectors primarily for analog audio signals. Invented in the late 19th century for telephone switchboards, the phone connector remains in use for interfacing wired audio equipment, such as headphones, speakers, microphones, mixing consoles, and electronic musical instruments. A male connector, is mated into a female connector, though other terminology is used.
Hot swapping is the replacement or addition of components to a computer system without stopping, shutting down, or rebooting the system; hot plugging describes the addition of components only. Components which have such functionality are said to be hot-swappable or hot-pluggable; likewise, components which do not are cold-swappable or cold-pluggable.
IEC 60320 Appliance couplers for household and similar general purposes is a set of standards from the International Electrotechnical Commission (IEC) specifying non-locking connectors for connecting power supply cords to electrical appliances of voltage not exceeding 250 V (a.c.) and rated current not exceeding 16 A. Different types of connector are specified for different combinations of current, temperature and earthing requirements. Unlike IEC 60309 connectors, they are not coded for voltage; users must ensure that the voltage rating of the equipment is compatible with the mains supply. The standard uses the term coupler to encompass connectors on power cords and power inlets and outlets built into appliances.
The DIN connector is an electrical connector that was standardized by the Deutsches Institut für Normung (DIN), the German Institute for Standards, in the mid 1950s, initially with 3 pins for mono, but when stereo connections and gear appeared in late 1950s, versions with 5 pins or more were launched. The male DIN connectors (plugs) feature a 13.2 mm diameter metal shield with a notch that limits the orientation in which plug and socket can mate. The range of DIN connectors, different only in the configuration of the pins, have been standardized as DIN 41524 / IEC/DIN EN 60130-9 ; DIN 45322 ; DIN 45329 / IEC/DIN EN 60130–9 ; and DIN 45326 / IEC/DIN EN 60130-9.
Schuko is a plug/socket system used in much of Europe. It is a registered trademark referring to a system of AC power plugs and sockets that is defined as "CEE 7/3" (sockets) and "CEE 7/4" (plugs). A Schuko plug features two round pins of 4.8 mm diameter for the line and neutral contacts, plus two flat contact areas on the top and bottom side of the plug for protective earth (ground). The socket has a predominantly circular recess which is 17.5 mm deep with two symmetrical round apertures and two earthing clips on the sides of the socket positioned to ensure that the earth is always engaged before live pin contact is made. Schuko plugs and sockets are symmetric AC connectors. They can be mated in two ways, therefore line can be connected to either pin of the appliance plug. As with most types of European sockets, Schuko sockets can accept Europlugs. Schuko plugs are considered a very safe design when used with Schuko sockets, but they can also mate with other sockets to give an unsafe result.
AC power plugs and sockets connect devices to mains electricity to supply them with electrical power. A plug is the connector attached to an electrically-operated device, often via a cable. A socket is fixed in place, often on the internal walls of buildings, and is connected to an AC electrical circuit. Inserting the plug into the socket allows the device to draw power from this circuit.
A banana connector is a single-wire electrical connector used for joining wires to equipment. The term 4 mm connector is also used, especially in Europe, although not all banana connectors will mate with 4 mm parts, and 2 mm banana connectors exist. Various styles of banana plug contacts exist, all based on the concept of spring metal applying outward force into the unsprung cylindrical jack to produce a snug fit with good electrical conductivity. Common types include: a solid pin split lengthwise and splayed slightly, a tip of four leaf springs, a cylinder with a single leaf spring on one side, a bundle of stiff wire, a central pin surrounded by a multiple-slit cylinder with a central bulge, or simple sheet spring metal rolled into a nearly complete cylinder. The plugs are frequently used to terminate patch cords for electronic test equipment such as laboratory power supply units, while sheathed banana plugs are common on multimeter probe leads.
IEC 60309 is a series of international standards from the International Electrotechnical Commission (IEC) for "plugs, socket-outlets and couplers for industrial purposes". They are also referred to as "pin & sleeve" connectors in North America or as "CeeForm" connectors in the entertainment industry. The maximum voltage allowed by the standard is 1000 V DC or AC; the maximum current, 800 A; and the maximum frequency, 500 Hz. The ambient temperature range is −25 °C to 40 °C.
Industrial and multiphase plugs and sockets provide a connection to the electrical mains rated at higher voltages and currents than household plugs and sockets. They are generally used in polyphase systems, with high currents, or when protection from environmental hazards is required. Industrial outlets may have weatherproof covers, waterproofing sleeves, or may be interlocked with a switch to prevent accidental disconnection of an energized plug. Some types of connectors are approved for hazardous areas such as coal mines or petrochemical plants, where flammable gas may be present.
In electrical and mechanical trades and manufacturing, each half of a pair of mating connectors or fasteners is conventionally assigned the designation male or female. The female connector is generally a receptacle that receives and holds the male connector. Alternative terminology such as plug and socket or jack are sometimes used, particularly for electrical connectors.
Electrical wiring in the United Kingdom is commonly understood to be an electrical installation for operation by end users within domestic, commercial, industrial, and other buildings, and also in special installations and locations, such as marinas or caravan parks. It does not normally cover the transmission or distribution of electricity to them.
An extension cord (US), extension cable, power extender, drop cord, or extension lead (UK) is a length of flexible electrical power cable (flex) with a plug on one end and one or more sockets on the other end. The term usually refers to mains extensions but is also used to refer to extensions for other types of cabling. If the plug and power outlet are of different types, the term "adapter cord" may be used. Most extension cords range from around 2 to 30 feet in length although they are made up to 300 feet (91.44 m) in length.
The Europlug is a flat, non-rewirable two-pole, round-pin domestic AC power plug, rated for voltages up to 250 V and currents up to 2.5 A. It is a compromise design intended to connect low-power Class II appliances safely to the many different forms of round-pin domestic power socket used across Europe. However, it is not compatible with the rectangular-pin BS 1363 sockets found in Cyprus, Gibraltar, Singapore, Malaysia, United Arab Emirates, Hong Kong, Ireland, Malta and the United Kingdom. By the standard, Europlugs must be non-rewirable and must be supplied attached to a power cord; anything else is non-compliant.
Tamperproofing is a methodology used to hinder, deter or detect unauthorised access to a device or circumvention of a security system. Since any device or system can be foiled by a person with sufficient knowledge, equipment, and time, the term "tamperproof" is a misnomer unless some limitations on the tampering party's resources is explicit or assumed.
A Y-cable, Y cable, or splitter cable is a cable with three ends: one common end and two other ends. The Y-cable can resemble the Latin letter "Y".
Laptop charging trolleys, also known as laptop trolleys or laptop carts, are mobile storage containers to charge laptops, netbooks and tablet computers en masse. The trolleys are predominantly used in schools that have replaced their traditional static ICT suites of desktop computers with laptops, but do not have enough plug sockets in their buildings to charge all of the devices.
Plugs and sockets for electrical appliances not hardwired to mains electricity originated in the United Kingdom in the 1870s and were initially two-pin designs. These were usually sold as a mating pair, but gradually de facto and then official standards arose to enable the interchange of compatible devices. British standards have proliferated throughout large parts of the former British Empire.
A microphone blocker is an adapter designed to prevent eavesdropping.