Extension cord
Encyclopedia
Power cable
A power cable is an assembly of two or more electrical conductors, usually held together with an overall sheath. The assembly is used for transmission of electrical power...
(flex) with a plug on one end and one or more sockets on the other end (usually of the same type as the plug). The term usually refers to mains (household AC)
Mains electricity
Mains is the general-purpose alternating current electric power supply. In the US, electric power is referred to by several names including household power, household electricity, powerline, domestic power, wall power, line power, AC power, city power, street power, and grid power...
extensions but is also used to refer to extensions for other types of cabling. If the plug and receptacle are of different types, the term "adapter cord" may be used. Extension cable is also used, but that has a distinct meaning from extension cord for many people.
Overview
Some extension cords also incorporate safety features, such as a polarized plug and receptacle, grounded terminals, a 'power-on' indicator, a fusible linkFuse (electrical)
In electronics and electrical engineering, a fuse is a type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection, of either the load or source circuit...
, or even a residual-current device
Residual-current device
A Residual Current Device is a generic term covering both RCCBs and RCBOs.A Residual-Current Circuit Breaker is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor...
(also known as a ground-fault circuit interrupter or GFCI).
Extension cords come in various lengths and thicknesses, and service duties. In general, the more power needed by the appliance, the thicker the cord should be (that is, larger wires
Electrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...
inside). Cords to be used outdoors, in wet areas, around oils, or exposed to sunlight for long periods should be selected for such specific service.
An extension reel
Reel
A reel is an object around which lengths of another material are wound for storage. Generally a reel has a cylindrical core and walls on the sides to retain the material wound around the core...
is an extension lead that rolls up, usually into the socket end, which in some cases has more than one socket on it (often 2 or 4). Another type of extension reel hangs near the plug end and permits the user to draw the cord out by grasping the socket end.
A power cord
Power cord
A power cord, line cord, or mains cable is a cable that temporarily connects an appliance to the mains electricity supply via a wall socket or extension cord. The terms are generally used for cables using a power plug to connect to a single-phase alternating current power source at the local line...
is similar but much shorter and designed to connect an appliance to a mains outlet. The female end mates with an appliance inlet.
Power strip
A power strip is a block of electrical sockets that attaches to the end of a flexible cable and allows multiple electrical devices to be plugged in. As such it can be considered a type of trailing socket though that term is more often used for single and double cable mounted sockets...
is a block on the end of a power cable with a number of sockets (usually 3 or more), often arranged in a line. This term is also used to refer to the whole unit of a short extension cord terminating in a power strip.
The term "extension cord" has been in use since at least 1946.
Restrictions
To avoid the need to roll-up any excess length, and to avoid the need for the user to cut the cord to size, extension cords are sold in prefabricated lengths 1 to 150 feet. The longer the cord the larger the diameter of the conductors (wire gauges are larger for smaller diameter wire) should be to minimise voltage drop.In the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
where the domestic voltage is 120 V, the National Electrical Code (NEC) prohibits the use of extension cords in a 20 A circuit unless they are of 16 AWG
American wire gauge
American wire gauge , also known as the Brown & Sharpe wire gauge, is a standardized wire gauge system used since 1857 predominantly in the United States and Canada for the diameters of round, solid, nonferrous, electrically conducting wire...
or larger (for example, 14 AWG or 12 AWG). As with other flexible cords, the NEC also prohibits their use where attached to building surfaces, or concealed inside walls, floors, or ceilings, above suspended ceilings, or where run through holes or other openings (windows, doors) in structures (with limited exceptions). Cords run across the floor should be covered with a suitable device to protect them from physical damage.
| Conductor Gauge American wire gauge American wire gauge , also known as the Brown & Sharpe wire gauge, is a standardized wire gauge system used since 1857 predominantly in the United States and Canada for the diameters of round, solid, nonferrous, electrically conducting wire... / count: |
Max amps Ampere The ampere , often shortened to amp, is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère , French mathematician and physicist, considered the father of electrodynamics... : |
Max length: |
|---|---|---|
| 16/2 | 13A | 50' |
| 10A | 100' | |
| 16/3 | 13A | 50' |
| 10A | 100' | |
| 14/3 | 15A | 50' |
| 13A | 100' | |
| 12/3 | 15A | 100' |
| 10/3 | 15A | 100' |
Within the United States, Underwriters Laboratories
Underwriters Laboratories
Underwriters Laboratories Inc. is an independent product safety certification organization. Established in 1894, the company has its headquarters in Northbrook, Illinois. UL develops standards and test procedures for products, materials, components, assemblies, tools and equipment, chiefly dealing...
certifies extension cords as complying with the NEC. Key standards are UL 817 for the entire extension cord, and UL 62 for the electrical cabling itself. The United States General Services Administration
General Services Administration
The General Services Administration is an independent agency of the United States government, established in 1949 to help manage and support the basic functioning of federal agencies. The GSA supplies products and communications for U.S...
also maintains a standard for extension cords, J-C-1270, that references the UL standards and provides additional critera.
Other countries also regulate the use of extension cables but the specific conditions and the nature of the regulation varies. In Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
and elsewhere where the normal domestic voltage is around 230 V, there is less risk of causing fire through overheating of cables for any given power due to the lower current. However most European extension reel cables now include an automatic current cut-out to avoid misuse of the cable. This requires manual re-setting if excess current is drawn through the cable. (American multi-plug cords also include such a device but single- or triple-outlet cords do not.)
An extension reel can only be used to carry full rated current when fully extended since the portion on the reel constitutes a concentration of the loss power (the result of its series resistance
Joule heating
Joule heating, also known as ohmic heating and resistive heating, is the process by which the passage of an electric current through a conductor releases heat. It was first studied by James Prescott Joule in 1841. Joule immersed a length of wire in a fixed mass of water and measured the temperature...
) which is not suitably dissipated unless most of the cable is unreeled to expose it to ambient air.
Signal cable extenders
Extension cords sometimes refer to cables that add to the length of signal transmission cables or combined signal/electrical cables (for example, USBUniversal Serial Bus
USB is an industry standard developed in the mid-1990s that defines the cables, connectors and protocols used in a bus for connection, communication and power supply between computers and electronic devices....
cables). They are more likely to be called "extenders" or "extender cables" or "cable extenders". Such extenders have one male and one female connector.
Lead content
The majority of extension cords sold in the United States contain lead in the PVC insulation sheathing. California Proposition 65 (1986)California Proposition 65 (1986)
Proposition 65 is a California law passed by direct voter initiative in 1986 by a 63%-37% margin...
requires manufacturers to warn consumers when products contain toxic chemicals. Many extension cords carry warning labels that advise consumers to wash their hands after handling them. There is currently no widespread movement in the USA to stop the manufacture of products containing lead.
The European directive, RoHS, restricts the use of hazardous materials like lead in the manufacture of electrical products such as extension cords.
External links
- Extension Cords at Underwriters Laboratories Inc
- A solution to the socket shortage? BBC News article
- http://x-tensioncords.com Informative site including safety information