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National Electrical Manufacturers Association (NEMA) as approved by American National Standards Institute (ANSI) published ANSI/NEMA WD 6 to specify Wiring Device dimensional specifications. The male and female cord ends identified in this document are categorized as Non-Locking Type and Locking Type.
The Locking Type which have curved blades that are oriented in a circular manner are commonly referred to as Twist-Lock which is a term first patented by Harvey Hubbell in 1929. We have provided the full list of NEMA configurations that have been specified. This does NOT mean the units are commercially available as many have never been put into production by the various electrical wiring device manufacturers. You will note in the cross reference that N/A (not available) appears several times to largely reflect the absence of a commercially produced NEMA product.
The various wiring device manufacturers have turned to alternate standards and products for locking devices rated 50 Amp and 60 Amp. We have listed IEC60309, California CS 50A, and Non-NEMA alternatives based upon comparable voltage, amperage, and phases. Form factor and pin array has not been considered for purposes of the alternative product listed.
National Electric Code (NEC) may also influence the options in which a wiring device is offered.