Using Cable Glands to Maintain NEMA Rating in Plastic Enclosures

Cable glands are a must have accessory: These little gadgets snuggle right into a cutout in an enclosure to maintain the watertight seal of your NEMA or IP rated electronics enclosure. Thus, cable glands allow you to customize your plastic enclosure to fit your board and application exactly, but still ensure your electronics are cozy and dry inside the housing.

The cable gland contains 3 main parts: a nut, the body with two threaded ends, and a cable nut. Polycase can machine the proper sized hole into any flat surface of our NEMA electronics enclosures, then the cable gland is fitted into the hole. Before securing the gland with the nut, a rubber gasket is inserted which helps protect against water entering the housing. On the opposite threaded end, there is an O-ring connected to a series of teeth. The cable nut goes over the O-ring and teeth, and screws onto the threaded end. As the cable nut is tightened, it causes the O-ring to seal around the wire, creating a watertight seal. Although each cable gland will securely seal around only one wire, multiple cable glands can be used on each electronic enclosure if more than one wire is used.

There are myriad sizes of cable glands available. How do you know you’re selecting the most appropriate size? First you need to know what size wiring you will be using. This will allow you to select the cable gland that will hug the wiring closely to protect against water and dust intrusion. Polycase offers 7 different sizes of NEMA-rated cable glands to fit a large range of wire sizes, described in the chart below:

Chart showing various NEMA-rated cable gland sizes offered by Polycase.

A side note on selecting wire: wire size is based on how much power you need running through the unit. Once you have determined the necessary power and wire size, you can select the properly sized cable gland. A couple resources for selecting the proper wire can be found here:

http://www.hardwaresecrets.com/article/181/14

http://electrical.about.com/od/wiringcircuitry/a/electwiresizes.htm

An additional benefit of using a cable gland, it can also act as a strain relief. This  protects the wire from bending, fraying, and splitting at the point of entry on the enclosure.