Some extension cords also incorporate safety features, such as a polarized plug and receptacle, grounded terminals, a 'power-on' indicator, a fusible link, or even a residual-current device (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 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.
In the USA 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 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.
Other countries also regulate the use of extension cables but the specific conditions and the nature of the regulation varies. In Europe 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 multiplug cords also include such a device but single- or triple-outlet cords do not.)
An extension reel 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. Such cables 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) which is not suitably dissipated unless most of the cable is unreeled to expose it to ambient air.
A power cord is similar but the socket end is designed to mate with a panel plug (usually IEC or figure 8 style) and is usually much shorter. With IEC connectors cables are frequently seen with a line plug and socket. These may be considered either as powercords (if IEC outlets are in use) or as extensions (if used to extend a powercord.)
A power strip 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.
Below is the Coleman Cable Inc specifications as given to consider run footage:
|Gauge:||Max Current (Amps):|
|16/2|| 13A 0'-50'|
|16/3|| 13A 0'-50'|
|14/3|| 15A 0'-50'|
Colors are assigned to cords, but they can be found across the gauges. 16 gauge is usually orange and used for heavy duty equipment. The other colors (Yellow, Green, Blue and Red) are used in lower gauges.
Extension cords may sometimes refer to cables that transmit data, electricity, or both (for example, USB extension cable). This type of cable comes in handy when certain USB plugs cannot fit into the hubs, such as a USB flash drive. But they are more likely to be called "extenders" or "extender cables" or "cable extenders".