Extension cord

Last updated July 07, 2024

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 (usually of the same type as the plug). The term usually refers to mains (household AC) 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 (0.61 to 9.14 m) in length although they are made up to 300 feet (91.44 m) in length.

Extension cords come in various colors, lengths, thicknesses and service duties. In general, the more power needed by the appliance, the thicker the cord needs to be (meaning larger wires inside). Cords which will be used outdoors, in wet areas, around oils, or exposed to sunlight for long periods of time should be selected for such specific conditions. 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.

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).

Some cords contain multiple female connectors in close proximity of one another; others have female connectors spaced along the length of the cord. Cords generally contain either grounded or ungrounded connectors. While a grounded male connector can be forced into an ungrounded female socket, this is unsafe.

Variations

A power strip with power indicator and individual switches for each socket (UK) Extensioncord.jpg — A power strip with power indicator and individual switches for each socket (UK)

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.

A removable power cord is similar but much shorter, and is designed to connect an appliance to a mains outlet. The female end mates with an appliance inlet.

Regulations

National Electrical Code (US)

In the United States the domestic voltage is 120 V, and the National Electrical Code (NEC) prohibits the use of extension cords in a 20 A circuit unless they are of 16 AWG or larger diameter (for example, 14 AWG or 12 AWG).

As with other flexible cords, the NEC also prohibits their use where attached to building surfaces, concealed inside structures (walls, floors, ceilings), above suspended ceilings, or run through holes or other openings (windows, doors) in structures. The NEC does contain exceptions although they are very limited.

U.S. extension cord specifications^[2]
Conductor gauge/wires	Max current	Max length
16/2	13 A	50 ft	15 m
16/2	10 A	100 ft	30 m
16/3	13 A	50 ft	15 m
16/3	10 A	100 ft	30 m
14/3	15 A	50 ft	15 m
14/3	13 A	100 ft	30 m
12/3	15 A	100 ft	30 m
10/3	15 A	100 ft	30 m

Within the United States, Underwriters Laboratories certifies extension cords as complying with the NEC. Key standards are UL 817^[3] for the entire extension cord, and UL 62^[4] for the electrical cabling itself. The United States General Services Administration also maintains a standard for extension cords, J-C-1270,^[5] that references the UL standards and provides additional criteria.

The NEC tries to reduce potential fire hazards by requiring that there be a receptacle within 6 feet (1.8 m) of every point along the wall in residences, reducing the need for extension cords.^{[ citation needed ]} However, even in houses with more receptacles than the code requires, there will sometimes be a need for extension cords.

Europe

In Europe and elsewhere where the normal domestic voltage is around 230 V there may be 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 resetting 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.)

Hazards

Fire incident history research has shown that a large proportion of structure fires are caused by extension cords that have been either damaged or overloaded.^{[ citation needed ]}

The insulation of extension cords, particularly light-duty two-wire cords, is easily damaged by being pinched, crushed, or abraded. The cords can also be damaged at the plug and socket connections by being pulled on excessively, which sometimes happens when people trip on them. Overloading can cause an extension cord to heat up to the point that its insulation either melts or carbonizes. Heating appliances may also cause heat damage to the insulation of a cord, melting or burning it away.

If the internal metal wires are damaged, such as by the cord being crushed in a door, then where the unbroken part of the wires is narrower than the bulk of the wires, this can form a point of high resistance. A hot spot may develop as the resistance of the narrower part of the wire is higher than the rest of the wire, and thus tends to concentrate power dissipation there.

Animals may chew on the wires and remove some of the insulation. In any of these cases if the damage is not noticed and the cord is not repaired or taken out of service, the damage can lead to arcing or a short circuit between the wires, which can ignite nearby materials. The exposed wires of an extension cord with damaged insulation can also present a shock hazard to people and animals.

Safety

Cords running across the floor should be covered with a suitable device to protect them from physical damage. However, they should never be covered with a rug or carpet, as this can produce a serious fire hazard.^[6]

To avoid the need for rolling-up excess length, using an extension reel or for cutting the cord to size, extension cords are sold in prefabricated lengths of 1 to 150 feet (0.30 to 45.72 m). Every foot of cord increases the electrical resistance, in turn decreasing the power the cord can deliver. Therefore, the longer the cord, the larger the diameter of the conductors needed to minimise voltage drop (wire gauge numbers are smaller for larger diameter wire). Because of this, it is best to use a cord that's exactly as long as needed and no more.

An extension reel can only carry full rated current when completely extended. This is because the portion of cord on the reel is not exposed to air causing the loss power, (the result of its series resistance), not to dissipate. An extension cord that is in use while coiled up or coiled in a reel can be a serious shock and fire hazard. The heat produced from the resistance cannot dissipate and is instead trapped between the tightly coiled cable, leading to the a fire or shock.^[7] Additionally, the ESFI recommends to never use an extension cord that is covered by a rug or blanket, or that is run through a ceiling or wall, since the heat may not be able to dissipate appropriately.^[6]

Lead content

Extension cords sold in the United States may contain lead in the PVC insulation sheathing. California Proposition 65 (1986) 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.

The European directive, RoHS, restricts the use of hazardous materials like lead in the manufacture of electrical products such as extension cords. Some manufacturers have moved to RoHS compliance^{[ citation needed ]} but there is currently no widespread movement in the US to stop the manufacture of products containing lead.^{[ citation needed ]}

Maintenance

The attention required to safely use an extension cord includes routing extension cords away from where they are likely to be damaged, using the shortest cord that will serve each intended purpose, and examining the cords periodically for damage or signs of overloading (melting deformation, darkening in color, or a “burnt” or “electrical” smell).

Periodic inspection is especially important for cords that may be used in place for a long time, for instance behind furniture, where damage may go unnoticed and by chance conditions are right for a fire or electrical shock incident to occur (e.g. some dust or paper falls near the arcing wire, or a liquid spill occurs and flows to the exposed wire).

Another dangerous modification to an extension cord is removing the third prong in order to fit sockets, which results in removing of the grounding prong, as well as loss of the hot/neutral prong distinction.

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, USB cables). They are more likely to be called "extenders" or "extender cables" or "cable extenders". Such extenders have one male and one female connector.

Passive USB extender cables do not meet the USB standards and thus are forbidden to carry the USB logo. The only cable structure recognized by the official USB standards is one with either a type A plug or a type C plug on one end, and either a type B plug or a type C plug on the other end (adapters with a type C plug and a type A or type B socket are also allowed, while adapters with a type C socket and a type A or type B plug or socket are explicitly not allowed^[8]). This restriction is intended to prevent cable lengths greater than the maximum allowed by the USB standard from being assembled and to avoid an accumulation of resistance in the connections exceeding the design limits of USB, in order to ensure consistent plug-and-play operation of the USB system without the need for users to calculate cable lengths or enforce technical rules.

The intention of USB is to make sure any standard-compliant cable can be used to connect any two compatible devices, and the connection will work, without question. To this end, the USB standard limits the maximum length of any compliant (and thus logo-bearing) USB cable (to about 15 feet). For a longer cable length, a USB hub is required. Despite being nonstandard, these extender cables are readily available from many sources.

Another class of USB extenders are actually USB hubs with a length of cable permanently attached. These do comply with the USB standard, if not more than a limited number of them are connected together. However, they require power from the USB connection and so may reduce the power available for the device at the "B" end.

Related Research Articles

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 DC connector is an electrical connector for supplying direct current (DC) power.

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.

A power cord, line cord, or mains cable is an electrical 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 voltage. The terms power cable, mains lead, flex or kettle lead are also used. A lamp cord is a light-weight, ungrounded, single-insulated two-wire cord used for small loads such as a table or floor lamp.

A power strip is a block of electrical sockets that attaches to the end of a flexible cable, allowing multiple electrical devices to be powered from a single electrical socket. Power strips are often used when many electrical devices are in proximity, such as for audio, video, computer systems, appliances, power tools, and lighting. Power strips often include a circuit breaker to interrupt the electric current in case of an overload or a short circuit. Some power strips provide protection against electrical power surges. Typical housing styles include strip, rack-mount, under-monitor and direct plug-in.

Electrical wiring in North America follows the regulations and standards applicable at the installation location. It is also designed to provide proper function, and is also influenced by history and traditions of the location installation.

<span class="mw-page-title-main">National Electrical Code</span> Electrical wiring standard

The National Electrical Code (NEC), or NFPA 70, is a regionally adoptable standard for the safe installation of electrical wiring and equipment in the United States. It is part of the National Fire Code series published by the National Fire Protection Association (NFPA), a private trade association. Despite the use of the term "national," it is not a federal law. It is typically adopted by states and municipalities in an effort to standardize their enforcement of safe electrical practices. In some cases, the NEC is amended, altered and may even be rejected in lieu of regional regulations as voted on by local governing bodies.

<span class="mw-page-title-main">AC power plugs and sockets</span> Connector used to connect to mains power

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.

<span class="mw-page-title-main">Banana connector</span> Single-wire electrical connector used for joining wires to equipment

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.

<span class="mw-page-title-main">Gender of connectors and fasteners</span> Male components insert into female components

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.

<span class="mw-page-title-main">Electrical wiring</span> Electrical installation of cabling

Electrical wiring is an electrical installation of cabling and associated devices such as switches, distribution boards, sockets, and light fittings in a structure.

A power cable is an electrical cable, an assembly of one or more electrical conductors, usually held together with an overall sheath. The assembly is used for transmission of electrical power. Power cables may be installed as permanent wiring within buildings, buried in the ground, run overhead, or exposed. Power cables that are bundled inside thermoplastic sheathing and that are intended to be run inside a building are known as NM-B.

USB On-The-Go is a specification first used in late 2001 that allows USB devices, such as tablets or smartphones, to also act as a host, allowing other USB devices, such as USB flash drives, digital cameras, mouse or keyboards, to be attached to them. Use of USB OTG allows devices to switch back and forth between the roles of host and device. For example, a smartphone may read from removable media as the host device, but present itself as a USB Mass Storage Device when connected to a host computer.

<span class="mw-page-title-main">NEMA connector</span> Power plugs and receptacles used in North America and some other regions

NEMA connectors are power plugs and sockets used for AC mains electricity in North America and other countries that use the standards set by the US National Electrical Manufacturers Association. NEMA wiring devices are made in current ratings from 15 to 60 amperes (A), with voltage ratings from 125 to 600 volts (V). Different combinations of contact blade widths, shapes, orientations, and dimensions create non-interchangeable connectors that are unique for each combination of voltage, electric current carrying capacity, and grounding system.

A stage pin connector, also known as a grounded stage pin (GSP), grounded pin connector (GPC) or theater paddle (TP), is a standard cable type for theatrical lighting in North America and in many countries in the theatre world.

<span class="mw-page-title-main">Modular connector</span> Electrical connector commonly used in telephone and computer networks

A modular connector is a type of electrical connector for cords and cables of electronic devices and appliances, such as in computer networking, telecommunication equipment, and audio headsets.

An automobile auxiliary power outlet in an automobile was initially designed to power an electrically heated cigarette lighter, but became a de facto standard DC connector to supply electrical power for portable accessories used in or near an automobile directly from the vehicle's electrical system. Such include mobile phone chargers, cooling fans, portable fridges, electric air pumps, and power inverters.

MC4 connectors are single-contact electrical connectors commonly used for connecting solar panels. The MC in MC4 stands for the manufacturer Multi-Contact and the 4 for the 4 mm diameter contact pin. MC4s allow strings of panels to be easily constructed by pushing the compatible connectors from adjacent panels together by hand, but require a tool to disconnect them to ensure they do not accidentally disconnect when the cables are pulled. The National Electric Code (NEC) and the UL6703 standard for PV connectors specify that connectors have to be from the same type and brand to avoid the dangers of cross-mating. In addition, IEC 62548 ‘design requirements for PV Systems' require PV connectors to be of the same origin. Originally rated for 600V, newer versions of the MC4 connector are rated at 1500V, which allows longer series strings to be created.

USB-C, or USB Type-C, is a 24-pin connector that supersedes previous USB connectors and can carry audio, video and other data, e.g., to drive multiple displays or to store a backup to an external drive. It can also provide and receive power, such as powering a laptop or a mobile phone. It is applied not only by USB technology, but also by other protocols, including Thunderbolt, PCIe, HDMI, DisplayPort, and others. It is extensible to support future standards.

The initial versions of the USB standard specified connectors that were easy to use and that would have acceptable life spans; revisions of the standard added smaller connectors useful for compact portable devices. Higher-speed development of the USB standard gave rise to another family of connectors to permit additional data paths. All versions of USB specify cable properties; version 3.x cables include additional data paths. The USB standard included power supply to peripheral devices; modern versions of the standard extend the power delivery limits for battery charging and devices requiring up to 240 watts. USB has been selected as the standard charging format for many mobile phones, reducing the proliferation of proprietary chargers.

References

↑ Addams Stratton McAllister, National Directory of Commodity Specifications: Classified and Alphabetical Lists and Brief Descriptions of Existing Commodity Specifications, Issue 65 National Bureau of Standards, United States. Bureau of Foreign and Domestic Commerce, U.S. Government Printing Office, 1925 page 230
↑ Coleman Cable Inc.
↑ UL 817 (2001-03-16). "Standard for Cord Sets and Power-Supply Cords". Archived from the original on 2014-02-01. Retrieved 2011-09-26.{{cite web}}: CS1 maint: numeric names: authors list (link)
↑ UL 62 (2010-05-18). "Flexible Cords and Cables". Archived from the original on 2012-03-14. Retrieved 2011-09-26.{{cite web}}: CS1 maint: numeric names: authors list (link)
↑ J-C-1270B (1973-10-05). "Cable Assembly, Power, Electrical". Archived from the original on 2012-12-12. Retrieved 2011-09-26.{{cite web}}: CS1 maint: numeric names: authors list (link)
1 2 "Extension Cord Safety Tips - Electrical Safety Foundation International". 6 January 2020.
↑ Kennedy, James (May 6, 2017). "Selecting Best Extension Cord for Every Situation".
↑ Universal Serial Bus Type-C Cable and Connector Specification Release 2.0 (Specification). USB Implementers Forum. August 2019. p. 32. USB Type-C receptacle to USB legacy adapters are explicitly not defined or allowed. Such adapters would allow many invalid and potentially unsafe cable connections to be constructed by users.

External links

Extension Cords at Underwriters Laboratories Inc
A solution to the socket shortage? BBC News article

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[1] Addams Stratton McAllister, National Directory of Commodity Specifications: Classified and Alphabetical Lists and Brief Descriptions of Existing Commodity Specifications, Issue 65 National Bureau of Standards, United States. Bureau of Foreign and Domestic Commerce, U.S. Government Printing Office, 1925 page 230

[2] Coleman Cable Inc.

[3] UL 817 (2001-03-16). "Standard for Cord Sets and Power-Supply Cords". Archived from the original on 2014-02-01. Retrieved 2011-09-26.{{cite web}}: CS1 maint: numeric names: authors list (link)

[4] UL 62 (2010-05-18). "Flexible Cords and Cables". Archived from the original on 2012-03-14. Retrieved 2011-09-26.{{cite web}}: CS1 maint: numeric names: authors list (link)

[5] J-C-1270B (1973-10-05). "Cable Assembly, Power, Electrical". Archived from the original on 2012-12-12. Retrieved 2011-09-26.{{cite web}}: CS1 maint: numeric names: authors list (link)

[auto-6] 1 2 "Extension Cord Safety Tips - Electrical Safety Foundation International". 6 January 2020.

[7] Kennedy, James (May 6, 2017). "Selecting Best Extension Cord for Every Situation".

[8] Universal Serial Bus Type-C Cable and Connector Specification Release 2.0 (Specification). USB Implementers Forum. August 2019. p. 32. USB Type-C receptacle to USB legacy adapters are explicitly not defined or allowed. Such adapters would allow many invalid and potentially unsafe cable connections to be constructed by users.

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