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The flat parallel plug blades are polarized to prevent the hot and the neutral connections from being reversed. In addition, many versions have a molded obstruction bump on top of the adapter, to block the grounding prong and thus physically prevent forcible insertion of a 3-prong plug in the wrong orientation.
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. These connectors are common on household backup generators, and on racks of power amplifiers in large audio systems.
Three-phase electric motors do not need the neutral wire to function, so that there is also a red four pin variant (3 phases and earth) of the IEC 60309 plugs for three phase power. The two styles are not intermatable, to prevent a potential floating neutral.
For power circuits, the color-coding uses the same colors as residential construction, and adds the additional wires used for three-phase systems. Black, Red and Blue are used for hot wires and White is used as the neutral wire in a 120/208 V circuit. Brown, Orange and Yellow are used as hot wires and gray is used as the neutral wire in a 277/ ...
In some designs, polarised plugs cannot be mated with non-polarised sockets. In NEMA 1 plugs, for example, the neutral blade is slightly wider than the hot blade, so it can only be inserted one way. Wiring systems where both circuit conductors have a significant potential with respect to earth do not benefit from polarised plugs.
The line to neutral voltage is half the line-to-line voltage. Lighting and small appliances may be connected between a line wire and the neutral. Higher-power appliances, such as cooking equipment, space heating, water heaters, clothes dryers, air conditioners and electric vehicle charging equipment, are connected to the two line conductors.
If colored white, it typically may be used for splicing neutral wires in a device box, while leaving a pigtail free for connection to a device (such as a receptacle). If colored green, the assembly is intended to be used as a grounding pigtail, similar to the feedthrough twist-on wire connectors without a permanently-attached wire.
Neutral is a circuit conductor that normally completes the circuit back to the source. NEC states that the neutral and ground wires should be connected at the neutral point of the transformer or generator, or otherwise some "system neutral point" but not anywhere else. [1]