NEMA 6 has three-wire grounding used for 208 and 240 V commercial or industrial devices. Figure 2: The obsolete NEMA 1 ungrounded connector (left) and the replacement NEMA 5 grounded connector (right). NEMA 5 has two poles, three wires with two blades, and a grounding pin. NEMA 4 was a planned series rated for 600 V with two wires NEMA 3 was a planned series rated for 277 V with two wires. NEMA 2 is also obsolete, it’s two-wire and rated for 250 V. NEMA 1 is not used in new designs it has been replaced by grounded configurations. NEMA 1 has two flat prongs for two poles, two-wire non-grounded connections rated for 125 V. The following is a brief overview of the 24 common NEMA connector classes:
As described below, the NEMA 7-15P plug is a grounded, two-pole plug rated for 277V and 15A. NEMA designations are divided into three elements, separated by a dash (-): the first number is the class and indicates the voltage, pole count, and whether it’s grounded the second number is the amp rating of the connector, and the third element is a letter indicating whether it’s a plug (P) or receptacle (R). In addition, a protective earth, or ground, contact may be present, in which case the socket is classified as two pole and earth (2P+E). Single-phase sockets are classified as two-pole (2P) and provide a single line contact and a neutral contact. Table 1: NEMA AC connector classes for grounded and ungrounded connections. There are 24 common non-locking NEMA connector configurations that fall into four voltage classes (Table 1). In Europe, the maximum current rating of IEC 60309 connectors is 800 A, voltage ratings are up to 1000 V, and the maximum frequency is 500 Hz. Typical ratings for AC power connectors meeting ANSI/NEMA WD 6 Wiring Device specifications in the US are 15 to 60 A, up to 600 V, and up to 400 Hz. This FAQ begins with an overview of non-locking and locking AC power connectors meeting National Electrical Manufacturers Association (NEMA) standards in the US and IEC 60309 standards in Europe and closes with a review of the requirements for hospital-grade AC connectors in North America. AC receptacles and plugs come in various configurations with different blade widths, shapes, positions, and dimensions, designed to make them safe to use and non-interchangeable with different combinations of voltage, current capacity, and groundings.
Power connectors are primarily designed to ensure a safe and reliable connection of devices to AC mains power, although they are generally specified for AC and DC voltages.
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