A guide to cable strain relief
Electrical strain relief fittings and bushings explained:
Whenever you're working with any type of conductor or cable, protecting them from damage is essential. When working with them inside or outside of an enclosure, this entails keeping them from undue strain, whether from an excessive bend radius, pulling or tugging, or from the cable sheathing itself.
There are a variety of cable and wire strain relief methods available.
Of course, when using voltage carrying conductors, protecting the cable also protects personnel and equipment from harmful exposure to electrical current. Let's start our guide there.
As mentioned, protecting electrical conductors from damage is essential from both an equipment- and human-protection standpoint. Often, some type of flexible metal conduit – sometimes with the wiring already installed – is used instead of a rigid type conduit.
Because of their spiral construction, the ends of the conduit can be sharp enough to cut through the conductor's insulation. To prevent an electrical short, internal wire strain relief must be used. This fits around the conductors and slides into the flexible conduit. The conduit is then inserted into the connector that is attached to a conduit junction box or electric cable enclosure.
For electrical cords with jackets, there are various types of wire strain relief methods. For example, cord grips, sometimes called cable glands, are a type of electrical cord strain relief that provides two types of protection for flexible cords. Not only does it prevent the cable insulation from being penetrated by the sharp edges of the enclosure or electrical box, but from being pulled out of the box as well.
Depending on the environment, you can use either a metal alloy or plastic cable strain relief grip. These electrical cable strain relief grips come in either a straight or angled configuration.
Some cable strain reliefs don’t provide protection from pulling force. Instead, they are used to allow cables to pass through holes in furniture, enclosures, and other surfaces without causing damage to either the cord or the device. For example, a universal bushing can be inserted into a hole drilled into a desktop and several cables of various sizes can be run through the bushing.
Some have a split design, as seen below, to adjust to the hole size, while others are of a fixed diameter. A carpenter or electrician will know how to install strain relief bushing types like this. Special cutting tools, such as a hole saw, are needed to install these bushing and ensure a snug, clean fit.
Compression strain relief bushing types
While often used for small or flat electrical cords, there are compression plastic strain relief bushing and grommet styles that are simple to install. In electronic equipment, they absorb push, pull, and twisting forces that the cord may be subjected to during use.
They snap into either a round or anti-rotation hole and when inserted, they compress against the cord or cable. To remove them for cord replacement, you can purchase a set of strain relief bushing pliers that make it easier. However, slip fit or channel locking pliers are often how many technicians remove strain relief bushing and cable installations.
Obviously, there are many electrical cord strain relief bushing and grommet options from which to choose. Consider the environment, purpose, and other special situations to ensure making the correct choice.
Fibre and low-voltage wire strain relief methods
When installing fibre optic cable and other low voltage cables like ethernet, you can use some of the same electrical strain relief bushing and grommet sets as with electrical cables.
However, there are some specialised cable strain relief bushing products made specifically for fibre and related cabling. Some products aren't bushings per se, but small radius bend and cabling smoothing in an enclosure. Because of the rather delicate nature of these cabling systems, you need to prevent kinking or an excessively small radius bend when installed.
Here are a few other options:
Limit the angle of 900-micron fibre when routing though holes
|Strain relief boot|
Transition from 3 mm jacketed fibre to a 900-micron fiber while limiting fibre bending
|900 micron transition boot|
Mount jacketed fibre to a panel or enclosure, preventing cable pull out and overbending of fibre
|Quick panel mount strain relief gland kit|
As with electrical cabling, take all environmental and occupational conditions into account when choosing the products you need for fibre installation.
Download free CADs and try before you buy
Free CADs are available to download for most solutions to help you optimise your design. You can also request free samples to ensure cable strain relief and protection you’ve chosen is exactly what you need. If you’re not quite sure which solution will work best for your application, our experts are always happy to advise you.
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