AC Power Plugs and Sockets: British and Related Types

NEMA L23 are four-pole and ground connectors rated for 347/600 V. Intended for wye three-phase circuits with both neutral and ground. NEMA L22 are four-pole and ground connectors rated for 277/480 V. Intended for wye three-phase circuits with both neutral and ground. NEMA L18 are four-pole no ground connectors rated for 120/208 V. Intended for wye three-phase circuits. NEMA L14 are three-pole and ground connectors rated for 125/250 V. Intended for three-pole, four-wire hot-hot-neutral-ground circuits with a nominal supply voltages of 240 or 208 V hot-to-hot and 120 V hot-to-neutral. NEMA L16 are three-pole and ground connectors rated for 480 V. Intended for three-phase circuits. Many event production companies use power distributors with camlock connectors for feeder cable, and 12 or more L21-30 connectors which can each be broken out to three individual 120 V circuits via the use of a stringer box. They are also found on some RVs for connecting to shore power. These versions of the 5-15R or 5-20R receptacle are residual-current devices, and have "Test" and "Reset" buttons (and sometimes an indicator light which may be normally on or normally off per the vendor's design). Of course, as many railways use the running rails for signalling circuits as well, special precautions have to be taken to protect them from interference.

NEMA L9 are two-pole and ground connectors rated for 600 V. Intended for three-wire hot-hot-ground circuits. NEMA L8 are two-pole and ground connectors rated for 480 V. Intended for three-wire hot-hot-ground circuits. They are intended for two-pole, three wire, line-line-earth (or hot-hot-ground) circuits with a nominal supply voltage of 208 or 240 volts, depending on phase configuration. This allows for cost-effective retrofits on older installations where branch circuits were often daisy-chained between wet and dry locations. In the US and Canada, GFCI protection is required for receptacles in many potentially wet locations, including outside outlets, bathrooms, and some places in kitchens, basements, and crawl spaces. GFCI devices come in many configurations including circuit-breakers, portable devices and receptacles. These benefits come with a trade-off of typically being double or triple the price of a comparable Monocable system. The first commercial needle telegraph system and the most widely used of its type was the Cooke and Wheatstone telegraph, invented in 1837. The second category are armature systems, in which the current activates a telegraph sounder that makes a click; communication on this type of system relies on sending clicks in coded rhythmic patterns. Unfazed, RCA continued to develop their own color television system that would be compatible with its customers RCA sets.

NEMA L12 series devices are three-pole, three-wire, non-grounding devices for three-phase 480-volt devices. Over time, electrical codes in the US and Canada began to require additional safety features in the basic NEMA 5-15R and 5-20R configurations to address specific electric shock hazard concerns. Despite its weaknesses, the tamper-resistant receptacle is superior to protective plastic outlet caps which must be individually installed on each receptacle (and are a choking hazard when removed), and to sliding covers that children easily learn to defeat. This is an expedient way to provide that protection at the receptacle itself. AFCI protection is mandated by the 2014 Code in residential family rooms, dining rooms, living rooms, kitchens, parlors, libraries, dens, bedrooms, laundry rooms, sunrooms, recreation rooms, closets, hallways or similar rooms. Installing a single receptacle is often cheaper or more convenient than providing this GFCI protection at the circuit breaker. Inserting a normal, two-blade electrical plug applies simultaneous pressure on both sides of the receptacle to open an internal, spring-loaded shutter, but a foreign object fails to do so and therefore cannot make contact with the live electrical contacts.

Maud Lucas Lancaster mentions an earthed iron-clad plug and socket by the English firm of A. Reyrolle & Company. In this application the "dedicated" socket refers to one that is not connected to a residual current circuit breaker, which is otherwise mandated for all normal power sockets. These connectors are common in live event power distribution. NEMA L13 series devices are three-pole, three-wire, non-grounding devices for three-phase 600-volt devices. NEMA L10 series devices are two-pole plus neutral, three-wire, non-grounding devices for 125/250 volts single-phase. Single-phase AC is used only for distribution to end users since it is not usable for large polyphase induction motors. NEMA L2 series devices are two-pole, two-wire, non-grounding devices for 250 volts single-phase. NEMA L5 connectors are a series of two-pole and ground locking connectors rated for 125 V. L5-30R receptacles are common at marinas that provide power to docked boats. RVs in the US are equipped for 120 V 30 A or 240 V 50 A service, and use a cord to connect to a receptacle at the campsite, usually on a power pedestal with one or more receptacles providing 120 V 30 A (TT30R), 240 V 50 A (14-50R), or 120 V 15/20 A (5-20R) service.

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