NEMA connector
[2] In the early days of electrification, residential use was almost exclusively for illumination, with rooms normally having just a single electrical outlet spot in the center.
[8] Since NEMA was a forum between manufacturers and not a governmental body, any decision had to be thoroughly discussed and agreed upon by its members, which substantially slowed the standardization process.
The numerals preceding the hyphen encode the number of poles (current-carrying terminals) and wires connected to it, the voltage, and single- or three-phase power.
The small hole near the end of the power (non-ground) blades of some NEMA plugs is used for convenience in manufacturing; if present, it must be of specified diameter and position.
[2] Small specialized padlocks are available to fit these holes, allowing "lockout" of hazardous equipment, by physically preventing insertion of locked plugs into a power receptacle.
This safety flaw has been exploited by a January 2020 Internet phenomenon known as the Outlet challenge, where conductive materials, usually coins or paper clips were dropped into the gap, causing electric sparks, which once led to a building evacuation in Westford Academy.
1-15R receptacles have been prohibited in new construction in the United States and Canada since 1962, but remain in many older buildings, and this obsolete design is still available for repair use only.
Standards permit ungrounded plugs where the appliance does not require grounding due to low risk of leakage current, such as on double-insulated devices.
The Electrical Safety Foundation International has stated: "Never remove the ground pin (the third prong) to make a three-prong plug fit a two-prong outlet".
[20] This is accomplished by an interlocking mechanism that requires hot and neutral blades inserted simultaneously to release the small doors blocking the slots.
In stage lighting for film and theater, the 5-15R connector is sometimes informally known as PBG (Parallel Blade with Ground), U-ground, or Edison.
[citation needed] NEMA 6 devices, while specified as 250 V, may be used for either 208 or 240 V circuits, generally depending on whether the building has a three-phase or split-phase power supply, respectively.
The NEMA 6-20R or 6-30R found in many hotel and motel rooms is typically supplied with either split-phase or two phases of three-phase 208 V. The higher-current receptacles are rare, with twist-locking plugs such as L6-30 and direct wiring being more common.
Generally, 6-series non-locking plugs are used for such appliances as large room air conditioners and commercial kitchen equipment; the occasional home arc welder also uses 6-50.
Safe operation relied on the neutral conductor in turn being connected to system ground at the circuit breaker or fuse box.
Modern practice is to require a separate safety grounding conductor whose only purpose is to divert unsafe voltages, and which does not carry significant current during normal operation.
[28] The 6-50 is a smaller size receptacle lacking a neutral fourth prong, exclusively providing 240 V, also used for electric vehicle charging station purposes.
The TT-30R receptacle is commonly available in nearly all RV parks in the United States and Canada, and all but the largest RVs manufactured since the 1970s use this plug to connect to power feeds.
The locking coupling makes for a more reliable connection in commercial and industrial settings, where vibration or incidental impact could disconnect a non-locking connector.
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.
L6-20 connectors provide a maximum of 20 amperes and are commonly found in power distribution units (PDUs) used in the information technology sector.
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.
[36] These safety devices work by comparing the currents flowing in the live and neutral conductors, and disconnect the circuit if their difference exceeds 4 to 6 milliamperes.
[citation needed] This safety measure reduces shock hazards to a child that attempts to insert a single conductive object into the receptacle.
Weather-resistant (WR) receptacles are made with ultraviolet-resistant insulating materials having excellent cold-temperature impact resistance to withstand longterm exposure to weathering and abuse.
Mandated by the 2008 National Electrical Code in outdoor damp or wet locations, WR receptacles are required in patio, deck, and pool areas.
[citation needed] These covers are ruggedly constructed to keep out moisture (either dripping or condensing), dust, debris, and insects, while providing easy access to receptacles to allow their use with power tools, trimmers, sprinkler systems, and pumps.
Two branch circuits may optionally share a common neutral wire terminating on duplex receptacles, a condition sometimes referred to as "split-wiring", "split-receptacle",[45] or "half-split".
[2] Underwriters Laboratories maintains UL Standard 498,[46] which specifies construction performance (e.g. durability, electrical safety, and fire-resistance) for NEMA connectors.
This specification references WD-6 and UL 498, and provides additional durability and electrical safety performance criteria for connectors intended for military use.
