Industrial Wiring Devices Overview for North America

wiring devices

In our last post, we covered IEC 60309 and Pin and Sleeve Wiring Devices.  Now, we will actually take a step back and provide a foundational understanding of the type of options that exist when operating in an industrial environment. Before we dive in, it’s worth noting that we are considering “industrial” to cover the full scope of the industrial sector. From “light” industrial settings such as a plug and receptacle powering a small piece of machinery in a non-manufacturing are to the processing line in a food manufacturing, this article should help guide you towards a practical electrical solution either way. Lastly, we are going to be covering this in order of descending popularity (i.e most popular devices will be covered first).

Without further ado, here are the major categories of electrical wiring devices in North America…

NEMA Straight Blade & Locking Devices

       NEMA Locking Wiring Devices

Perhaps the most popular devices in the United States, NEMA locking devices, sometimes more commonly referred to as “Twist Locks”, are a means of energizing and de-energizing electrical equipment. They are called twist locks because once you make an electrical connection, you can lock the device in place. Each voltage/amperage has its own color coding (much like IEC Pin and Sleeve). This prevents operators from trying to de-energize under load which could creating arching and fatal error.  Most NEMA Twist Locks are 125 or 250V, single phase electricity but 3 phase, 480V is also a feasible configuration. The highest amperage option is 30A and anything higher than that would require a different type of device. Additionally, they only go up to 4 wires (no neutral pins exist for a 5th wire). The manufacturer with the most market share in the US is Hubbell-Kellems.

Nema twist lock wiring devices

Great when
  • Dry Areas
  • Low Amperage
  • Locking Devices Necessary
Bad For
  • Heavy Industrial Applications
  • Wet Areas/Washdown

      NEMA Straight Blade Wiring Devices

Straight Blade devices share many of the same qualities as Twist Locks. They can actually go up to 60A obvious but will not support any 3 phase configuration other than 3 phase, 250V. The obvious downside here is that there is no locking mechanism within the devices. This creates a potential safety issue. However, if there is no need for de-energizing the equipment or only very experienced operators will be dealing with it, it may be a risk worth taking.

nema straight blade wiring devices

Great when
  • Cost matters
  • De-energization Risk Low
Bad For
  • Heavy Industrial Applications
  • Wet Areas/Washdown
  • High Usage (plugging, unplugging frequently)

Watertight NEMA Straight Blade & Locking Wiring Devices

As you may have imagined, Twist Locks have evolved over the years and offered versions that are most water-resistant. These have given them higher IP Ratings such that many of these devices are now IP65, 66, or 67 rated. All of the watertight devices are yellow by industry standard. To be clear, they are still voltage rated by color (blue, red, black, etc.)and will be marked on the device but the housing itself should always be yellow. In the market, you will frequently hear these mentioned as “yellow goods”. Just as with the non-watertight devices, these commonly only go up to 30A. The most common manufacturer of yellow goods in the US is Woodhead. In fact, they are so popular that you may hear them used interchangeably in the field (even though we are showing Hubbell below).

watertight nema wiring devices


Great when
  • Water Present
  • Lower Amperages
  • Visibility Needed (always yellow)
Bad For
  • Low Operator Experience (all yellow, inexperience may try hard to mate)
  • Caustic Environments

IEC Pin and Sleeve Wiring Devices

We’ve covered Pin and Sleeve in some detail already. However, we have yet to stack it up against its peers in the US market. Following Twist Locks, Pin and Sleeve are probably the second most popular category of electrical wiring devices and some of its benefits are nuanced yet important. For starters, you’ll notice that the pins are always shrouded. This prevents this pins from warping if dropped as well as would help contain any arching that may occur. The pins are also usually brass which isn’t malleable. We’ve heard horror stories where operators are able to take Twist Lock devices and bend the pins to fit and electrocuting themselves.

As has been noted before on this blog, Pin and Sleeve devices are usually IP 67 whereas only some Watertight Twist Locks/Straight Blades meet that requirement. It follows that Pin and Sleeve are very frequently used in 3 phase, high voltage applications as well as high current (60 and 100A). Additionally, some Pin and Sleeve products have a keyhole to allow for OSHA Lockout/Tagout during maintenance. Most manufacturers use material that is corrosion resistant as well which is why you see a lot of Pin and Sleeve in food manufacturing or chemical applications. In the US, Hubbell and Mennekes are the two market leaders.

Mennekes Pin and Sleeve wiring devices

Great when
  • Caustic/Harsh Environment
  • High Amperage
  • Lockout/Tagout
Bad For
  • Lower Amperage (can be overkill)
  • Cost Sensitive Buys

Switch-Rated Wiring Devices

These are a cousin (or sometimes brother) of IEC 60309 Pin and Sleeve Devices. They are a combination of a Pin and Sleeve but have a mechanism, usually a button, that allows the load to be de-energized within the housing of the device. Another phrase for this would be “disconnecting under load”. This means that the risk of arching is lower. It is also “Switch Rated” whereas normal IEC Pin and Sleeve devices are “Load Rated”. They are also usually NEMA4X (similar to regular P&S) rated and carry a IP 69K rating (whereas only some regular IEC 60309 devices have this designation). For a long time, Meltric was the only player in this market. Recently, Hubbell released their Advantage product; it’s uptake remains to be seen.

meltric switch rated wiring devices

Great when
  • Arch Risk High
  • Water Heavy Environments
Bad For
  • Cost Conscious Buyer (usually higher cost than regular Pin and Sleeve)
  • Caustic/Harsh Environments
  • Disconnecting frequently (usually harder to mate)

Explosion Proof Wiring Devices

We felt it was important to add a section on Explosion Proof (EX) devices. While not necessarily a product group specifically (there are explosion straight blade NEMA, IEC, and Switch Rated products), the designation itself is extremely important if the application calls for EX-proof devices. Popular EX-proof Wiring Device manufacturers would be Hubbell Killark and Appleton. In the field, Explosion Proof will also be referred to as “Class Rated”. Grainger does a good job of explaining it in further depth here.

Grounded Wiring Devices

In the “old” days of US manufacturing, the Pin and Sleeve products were metallic. Thus, there was no necessity for a grounding pin and the metallic shell of the plug/connector acted as the grounding agent. This is now called Style 1. In more recent years, the same metallic devices added a ground pin for additional grounding and it was called Style 2. Hubbell does a nice job of explaining the difference below in their catalog:

Style 1

Receptacles achieve grounding by attaching the ground conductor to the ground screw inside the back box and utilizing the metallic receptacle shell as a ground source (see 3P 4W Style I illustration). Plugs and connectors establish grounding by means of connecting the flexible cable ground conductor to a ground terminal within each device, which, in turn, is grounded through the metallic plug or connector shroud. Any exposed metallic components are suitably grounded in the Style I offering.

Style 2

The Style II ground path offers two means of achieving the proper ground path. In addition to utilizing the same grounding method as in the Style I product, the Style II version incorporates a separate ground pin and sleeve (see 3P 4W Style II illustration). This provides a second ground path. The ground pin on Style II devices is longer than other pins, meaning that they “make first” and “break last,” assuring protection for people and equipment.


Wrapping It Up

NEMA devices own the US market. Pin and Sleeve follow in popularity and Switch Rated come next. Lastly, there are more niche applications for Explosion Proof and Grounded devices.

What did we miss? Let us know in the comments below!