What is a Locking Plug?

Locking plug is known as NEMA connectors. NEMA stands for the National Electrical Manufacturers Association, a USA-based organization that forms a set of globally recognized and internationally applied standards for the manufacturing of electrical equipment. These standards outline the voltage and amperage configurations of plugs and receptacles to make it easier for consumers to differentiate them. NEMA connectors, including power plugs and receptacles, are among the electrical product categories covered by NEMA standards. They are everywhere in North America and other countries that use the standards. A NEMA male locking plug has two flat prongs placed either in parallel or perpendicular position (for higher currents/heavy duty applications) and it may also have a round or U-shaped ground pin below the flat blades used for grounding.

NEMA wiring devices are made in current ratings from 15 to 60 amperes (A), with voltage ratings from 125 to 600 volts (V). Different combinations of contact blade widths, shapes, orientations, and dimensions create non-interchangeable connectors that are unique for each combination of voltage, electric current carrying capacity, and grounding system.

NEMA connectors mainly include two types, that is, straight-blade, non-locking types and curved-blade, twist-locking types.

Straight-blade, non-locking types

Non-locking locking plugs feature flat-prong plugs that are designed to be pulled in and out of receptacles freely, which is convenient but is very likely to be disconnected by accident. They are commonly used for computers, household appliances and everyday applications where electrical devices are not required to be constantly turned on.

Curved-blade, twist-locking types

Twist-locking locking plugs have curved prongs that can be twisted after being inserted into the receptacle, to be locked in place. To unplug, the plug must be rotated in the reverse direction. Without this step, the plugged electrical devices cannot be disconnected, thus eliminating the risk of accidental disconnection and adding a layer of protection to electrical appliances. The locking coupling makes for a more reliable connection in commercial and industrial settings, where vibration or incidental impact could disconnect a non-locking connector.

Understanding NEMA Codes/It’s fairly easy to understand the designations. Power plugs and receptacles manufactured according to NEMA standards follow this general naming scheme. The number following the NEMA indicates the design features of a connector, which is preceded by a letter “L” in twist-locking devices. The second number that follows the dash represents the ampere rating of the connector. The final capital letters "P" and "R" stands for plugs and receptacles, respectively.

What are the features of a NEMA connector?

Taking NEMA 5 series as an example.

• NEMA 5 are the most common of the non-locking locking plugs where you have a hot and neutral wire and for a third prong an additional ground pin. Among others, NEMA 5 connectors rated at 15 and 20 Amps are used extensively in households.
• NEMA 5-15P is a two pole, 3 wire grounded plug rated up to 125V AC and 15 Amps. The ground pin can be either a round shape or a U shape. It’s composed of a molded rubber body and prongs of zinc-plated steel or brass. The NEMA 5-15 outlet is the standard household plug in the US used to connect small appliances such as TVs, microwaves, hairdryers etc. to a wall socket or a power supply receptacle. If you have a NEMA 5-15 outlet, you’ll find that you can plug practically anything in that you want.
• The NEMA 5-20P is a 3-prong grounded plug featuring two blades and one ground pin rated up to 125V AC and 20 Amps. Compared to the 5-15 plug, the 5-20 plug has a horizontal hot blade and a vertical neutral blade. The NEMA 5-20P is used in applications that require higher power draw such as large refrigerators, space heaters, large kitchen mixers, etc.
• NEMA 5-20R has a T-shaped neutral hole that’s intended to accommodate a perpendicular prong and allows users to plug in either a 5-20P or a 5-15P plug, making for more flexible connection. The NEMA 5-20 T-Slot wall outlet is the standard type found in homes and commercial buildings across the US.
• NEMA connectors all have unique pin positions to prevent connecting a higher rated plug to a lower rated receptacle which might cause an electrical fire. Occasionally NEMA connector pin layouts are designed so that plugs with lower ratings can be connected to receptacles with higher power ratings for greater flexibility. For this reason, the NEMA 5-15 plugs can connect to both the NEMA 5-15R and NEMA 5-20R outlets.
• There are many other non-locking and twist-locking types with many other amperage and voltage combinations in NEMA 5 series. Also, more types and configurations are available in the NEMA connector family that are targeted to meet a greater variety of applications.

At ATO online store, we offer configurations 5, 6, 14, 16, 17, 22, 23 with several of them also available in twist-locking types. Each of these configurations have their own specific uses. To get locking plugs today at the best price or for assistance in choosing the best one for your application. If you want to know more about ATO NEMA connector, view the video below.