The plug. That simple device affixed to the end of a power cord that moves power from the outlet or power strip to the appliance. The plug is often overlooked as a mere commodity component, but smart designers know that it can play a pivotal role in the overall design of a product and serve as a product differentiator.

Cord and plug suppliers now have a multitude of standard options, and can offer a plethora of customized products. Greg Ruppert, president of Quail Electronics, a Livermore, Calif.-based manufacturer of plugs, cords and cordsets, says that plugs are often one of the last things that designers think about in the design phase, but the market is filled with many new and innovative plug products.

Some plugs are made to be easily removed from the outlet. Photo: Quail

In fact, while amperages and voltages don’t change that much, the market place offers a burgeoning array of options. Today plugs come in more than just right angles and left angles, suppliers now offer something for everyone — slim profiles, locking plugs, quick-release plugs, even plugs that go around and around.

Because product designers often do not know where and into what type of outlet the equipment will be plugged, Quail, and other companies, offer plugs that rotate. Quail’s Rotating Plug can be turned 360-degrees in either direction so that the user can find the most appropriate angle for the application. The plug is NEMA 5-15P rated, meaning it can handle up to 15 amps.

The other advantage to the plug is that it has a profile of 1/2-in. Because space is often a consideration, a number of companies offer slim profile plugs that can give as much as an inch of additional room in which to work.

Lock in the power

These plugs are used in high-powered applications where it is critical for products to remain locked. Photo: Quail

Most plugs used in North America are standardized under a system of patterns and numbers created by the National Electrical Manufacturers Association (NEMA) that relate to the amperage and voltage. Depending on the power requirements and applications, plugs can be configured in a variety of ways.

Some of the newest plug products center around ensuring that the plug is not accidentally pulled from an outlet. Because there are many applications where a disruption of power is critical, such as in medical or computer environments, locking plugs can be crucial. Traditional locking plugs have blade configurations that allow the plug to be inserted into the socket and twist locked into a twist-lock receptacle. Twist locks come in a variety of maximum voltage and current capacities. For example, Conductive Cable, Rancho Santa Margarita, Calif., has six versions of its twist locks. The plugs, in the company’s CP line, include: 125V and 15A or 20A; 250V and 15A or 20A; and, 277V and 15A or 20A.

These plugs are notated by an L in front of the model numbers, such as the L5-15P that is a locking plug rated at 15 A at 125 VAC.

The ends of these hospital grade plugs are clear to make sure the connections are secure and in the correct location. Plugs can be lit as an option to make them easier to locate and to ensure that power is still flowing to the outlet. Photo: Quail

These plugs come assembled and in disassembled packages. Greg Ruppert says that plugs that need to be assembled have the possibility that they can be put together incorrectly and can come loose or disconnected inside of the plug. Instead, Quail offers molded versions of the heavy-duty locking plugs that are electrically tested “so that there is no chance that they can shake loose and become disconnected.”

Beyond the locking blade configurations, suppliers are now offering new types of locking plugs. Quail Electronics offers the Safety-Lock system, which was introduced in June 2006, which is available for low-amperage applications and higher-amperage applications such as servers and certain types of medical equipment.

The system comes in two options. In one, it comes packaged on a new plug and the user only needs to put on the mounting plate and screw it into the inlet. The system is also sold separately and can be retrofitted onto previously purchased Quail cords.

Another company offering a safety lock is Volex of Indianapolis, which recently introduced the V-Lock. The plug uses a locking and release button on the equipment end. The V-lock will be sold in standard kits or, depending on the run size, in lots.

The V-lock locks in the plug at the equipment end and helps ensure against accidental unplugging. Photo: Volex

Because locking plugs are used in critical situations, they often undergo insertion withdrawal tests, in which a 55-lbs. weight is hung from the cord and plug. In the case of the V-lock, these tests helped ensure that it will hold up to 25 KG withdrawal force, says Steve Cloyd, Volex’s application engineer.

In addition to ensuring that the plug doesn’t get prematurely withdrawn, the V-lock eliminates other locking solutions such as a bail latch, says Mary Foreman, Volex’s engineering manager. A bail latch is an add-on solution that snaps around the back of the plug. However, that hasn’t always been the answer because the connector body is not always the same size.

George Adams, Volex’s national distributor sales manager, adds that designers will need to specify the inlet as well as the cord. The inlet has a small notch that has a locking feature and the mating part to the cord. “There are two pieces to the V-lock solution,” he says. “Designers can’t use a V-lock cord with a standard inlet, they would need to spec that in as well.”

Both products are UL and CSA (Canadian Standards Association) approved and are compatible with IEC standards such as IEC 60230 that applies to plugs, as well as connectors, outlets and inlets that are used on electrical or electronic equipment such as portable computers, printers and medical equipment.

These pins and sleeves protect against dust and moisture. Photo: Interpower Corp.

While suppliers want to make it more difficult for a plug to disconnect accidentally, they also want to make it easier to disconnect intentionally, be that from a tight fitting wall outlet or a cramped power strip. Some plugs today are fitted with levers, which are sometimes called pull-tabs, that push the plugs from the outlet as it is unplugged. “With these easy pull applications, you don’t have to yank the cord out the wall and out of the outlet,” says Xavier Carbonel, marketing director for Quail.

Volex’s Foreman also suggests that designers that may face potential side-to-side force may choose a plug with a bigger face to reduce the force exerted on the blades. The company also offers what it calls the Pivot Plug (PH772), which is often used in vacuum-cleaner applications. The Pivot Plug has wings on either side that restrict the lateral angling of the plug as it is pulled from the outlet, which minimizes bending of the plug blades.

High and dry

A plug is locked in place and protected against moisture. Photo: Interpower Corp.

Bent blades are not the only hazards that a plug may face in the field. Some plugs maybe subjected to moisture, and for those applications there are products rated for ingress protection (IP).

At Oskaloosa, Iowa-based Interpower Corp., for instance, the company offers pin and sleeve devices that are IP 67 rated. An IP rating relates to the dust and moisture protection that it offers. The ‘6’ refers to dust and other particulates and is the IEC’s highest rating. The ‘7’ means that the product is protected against temporary immersion in water and other liquids. A lid on a socket protects the ingress, and also locks the plug in place.

For Interpower, these IP products are found on their high-powered pin and sleeve products. While in North America, the most common plug is the NEMA 5-15P, sometimes that is not adequate to the application. Some of Interpower’s products are rated to 415 VAC and 125 A for international applications and up to 480 VAC and 180 A for North American applications and the plugs include single-phase and three-phase systems.

Applications for high-powered products vary greatly, says Ralph Bright, marketing manager at Interpower. One application where they are often found is in fast food restaurants where commercial appliances such as ovens and dishwashers require high voltage and amperage ratings. In these kitchens, moisture and chemicals, as well as high temperatures, can be a problem that IP rated pins and sleeves can solve.

These products conform to IEC 60309, a standard that was designed to standardize high-powered products around the world. It defines a family of connectors that can be used for domestic and international markets. Much as NEMA has a standardized system of blade and pin configurations, the IEC has developed “clock” and color keys (see Fig. 1 and Fig. 2) to ensure polarity and avoid “mismating” connectors, Bright says.

Enlarge this picture Fig. 1. This color-coded chart shows the IEC 60309 operating voltages. Source: Interpower Corp.

“They don’t want you to mix and match plugs,” he adds, “so you are not trying to pull 230 volts and 20 amps out of something that can only handle 120 volts and 15 amps. “

Fig 2. This clock system helps ensure polarity and “mismating” of connectors. Source: Interpower Corp.

Light the way

A piggy-back plug from Volex.

Plug suppliers can customize and personalize their products in many different ways ranging from embossing to having colored plugs and cords to match a particular design need. They can be packaged differently or tagged with various labels.

Lighted plugs are also a relatively new innovation. Quail and Volex both offer a lighted plug or connector. Made from clear PVC, when the plug is lit, it indicates a live circuit that with one look will ensure that power is getting to the outlet and to the product. This could be important in cases of power surges that may knock out the power. In addition, it helps make the outlet or power strip easier to find in dark work areas or behind equipment or office furniture.

Volex’s lighted plug, the AEC30 is a 5-15P plug with clear PVC compound encasing the wiring and a standard bulb or optional neon bulbs or bulbs in different colors. Quail’s lighted products utilize LED illumination.

This 3-pole right-angled connector is also available as a straight connector.  Photo: Volex

In the cases of appliances that may be vulnerable to EMI/RFI issues, cables can be shielded with foil wrap and plugs can be fitted with ferrite beads. These beads are an iron core component that are attached around a power cord at either end of the cord to help filter EMI/RFI. Conductive Cable offers the CP-24 light duty, EMC filtered plug with a maximum 15 A and 125V.

Cords are basically big antennas, as Ruppert calls them, and they can pick up interference directly from the wall outlet, or from the surrounding environment as the power travels between the outlet and the equipment. The result is dirty power, that is, power carrying unwanted and undesirable signals along for the ride.

Carbonel says that there was one medical application where this was an important consideration in patient health. The product sent an electrical pulse meant to stimulate tissue and heal wounds, but it seemed to have the opposite effect. The electrical energy was being affected by EMI/RFI and creating dirty power. After a ferrite bead was added to the power cord, the unit began to operate properly.

“It is amazing that such a small characteristic could affect the outcome of a product,” he says. “But, it did.”

This straight plug for the European market complies with the IEC 60884-1 standard, which means it can be used for household and similar purposes. Photo: Volex

SIDEBAR | The ‘Hole’ Idea |

A plug is a plug is a plug, unless it is more than that. In the case of one plug, it became a company’s symbol of innovation.

The Assist Plug from Australia-based Breville was first developed in 1987 and soon became a company symbol that was incorporated into the kitchen appliance manufacturer’s business cards and stationary.

Developed first for the Australian market and now in use around the world on every Breville appliance sold, the Assist Plug features a finger “pull” to make pulling the plug easier for the user. Its development came as a response to consumer complaints about the difficulty of removing the plugs. Richard Hoare, Breville’s Innovation Director, Housewares International, says that the company felt there had to be a better way and began R&D work on a cost-effective solution. 

What they developed was simple and elegant. The Australian plug had a vertical loop that needed to be behind the pins (blades). This meant designing an inner chassis to direct the wires below the loop, Hoare says. When it came time to export the design, other considerations came to the fore. For instance, the Assist Plug for North America required a different design. In this case, the loop is horizontal and the wires pass through either side of the loop. The design also needs to accommodate two and three pin plugs as well as several sizes of cord.

Hoare says that the challenge was to design a plug with an adequate finger hole size, with enough room for the wires, without being too large for standard socket requirements.  Manufacturing and cost constraints also created limits to the design. “We needed a design that could be made in high volume at the right cost so we could afford to use it on every appliance, he adds.

The design process started with simple mockups to test ergonomics and progressed to 3D CAD models that were used to create rapid prototypes for further testing. The shape and size of the hole required considerable tuning and refinement, he says and that process began using anthropometric data — data that refers to measuring body parts to better understand physical variations — on the range of sizes of human fingers.

Hoare says that numerous tests were performed using people with various finger sizes. The company determined that the hole needed to accommodate the finger to between the first and second knuckle. The initial hole size was determined and the plug underwent more testing by people with myriad finger sizes and then the hole was shaped for comfort.
Since the success of the Assist Plug, the company has used the concept of a loop for improved grip in many other applications, including a better way to remove a blender lid and kettle lid, and as a way to move a hot espresso steam wand. 

“We thought there had to be a better way,” says Hoare. “Since its release we have received many letters from consumers praising the Assist Plug for its ease of use. I have spoken to a consumer who said his wife couldn’t plug and unplug the cooking appliances she needed to use without his help. Now with the Assist Plug she can cook when he’s out of the house.”