With an array of numbers, letters, and dashes, trying to decipher the National Electrical Manufacturers Association (NEMA) designations for plugs, connectors, and receptacles can be confusing. This guide will explain what they all mean for the most commonly used.
NEMA Terminology Glossary
Below is a short glossary to help clarify some of the terminology.
Receptacle:
Often referred to as an outlet, it's a female flange or box mounted wiring device with the conducting elements recessed behind the mating surface. Typically wired to be live when nothing is plugged in to it, receptacles are wired to the power source.
Inlet:
A male flange or box mounted wiring device that has its conducting pins exposed and protruding. It should never be wired so the exposed pins are live, or hot, when the mating device is not plugged in.
Connector:
A female cord mounted wiring device with its conducting elements recessed behind the mating surface. It's normally wired to be live when nothing is plugged in to it. Because of this, connectors are wired to the source of power.
Plug:
This is the common male cord mounted wiring device; the conducting pins are exposed and protruding. It should never be wired to make the exposed pins live while it's unplugged. Until they are plugged in to a power source like a wall outlet or generator outlet, these are always dead.
Common NEMA Configurations
The following chart illustrates the most common NEMA configurations used in North America for 125VAC and 250VAC single phase systems. Note that twist-lock devices lock in the mating position, and use curved blades. Once pushed into the receptacle, the plug is twisted and its now-rotated blades latch into the receptacle. Twist-locking makes for a more reliable connection in industrial and commercial settings, where accidental impact or excessive vibration might otherwise disconnect a non-locking connector.
While it may be a bit confusing when trying to determine just what all the NEMA plug information means, it's all very necessary. The reason for having such a wide variety is to prevent incorrect combinations of electrical systems being plugged together, thereby avoiding a potentially dangerous situation.
Product Compliance and Suitability
The product statements contained in this guide are intended for general informational purposes only. Such product statements do not constitute a product recommendation or representation as to the appropriateness, accuracy, completeness, correctness or currentness of the information provided. Information provided in this guide does not replace the use by you of any manufacturer instructions, technical product manual, or other professional resource or adviser available to you. Always read, understand and follow all manufacturer instructions.