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A non-grounded device may be two-pole, two-wire; three-pole, three-wire; etc. [citation needed] The numerals following the hyphen is the current rating of the device in amperes. This number is followed by the letter 'R' to indicate a receptacle (socket) or 'P' to indicate a plug (prongs).
Portable appliances use single-phase electric power, with two or three wired contacts at each outlet. Two wires (neutral and live/active/hot) carry current to operate the device. [3] [4] A third wire, not always present, connects conductive parts of the appliance case to earth ground. This protects users from electric shock if live internal ...
NEMA 5-20R outlets, which are similar to type B but have a T-shaped neutral slot, are sometimes used for higher current 120 V commercial equipments (up to 20 A). On the other hand, NEMA 10-50P outlets are sometimes used for 208 V and 240 V industrial equipments (up to 50 A). Comoros: C, E 220 V 380 V 50 Hz Congo, Republic of the: C, E
This practice arose from the three-wire system used to supply both 120 volt and 240 volt loads. Because these listed appliances often have components that use either 120, or both 120 and 240 volts, there is often some current on the neutral wire. This differs from the protective grounding wire, which only carries current under fault conditions.
With the advent of switch-mode supplies, adapters which can work with any voltage from 110 VAC to 240 VAC became widely available; previously either 100–120 VAC or 200–240 VAC versions were used. Adapters which can also be used with motor vehicle and aircraft power (see EmPower ) are available.
A wire or cable has a voltage (to neutral) rating and a maximum conductor surface temperature rating. The amount of current a cable or wire can safely carry depends on the installation conditions. The international standard wire sizes are given in the IEC 60228 standard of the International Electrotechnical Commission.
In both those instances the white wire should be identified as being hot, usually with black tape inside junction boxes. The neutral wire is identified by gray or white insulated wire, perhaps using stripes or markings. With lamp cord wire the ribbed wire is the neutral, and the smooth wire is the hot. NEC 2008 400.22(f) allows surface marking ...
BS 546, "Two-pole and earthing-pin plugs, socket-outlets and socket-outlet adaptors for AC (50-60 Hz) circuits up to 250 V" describes four sizes of plug rated at 2 A, 5 A (Type D), 15 A (Type M) and 30 A. The plugs have three round pins arranged in a triangle, with the larger top pin being the earthing pin.