Wiring Harness News WHN Sept-Oct 2020 WHN Sep-Oct 2020 - Page 31

INDUSTRIAL INFO-TAINMENT Wiring Harness News SEPTEMBER/OCTOBER 2020 31 Strain-Relief: Design Tips for Durability and Aesthetic Appeal Continued from page 29 ____________ tecting it from tight bends and fatigue loading. But how much is enough? Of course, you can take the strain equations from bend radii, correlate the strain with stress using the modulus of elasticity of the particular cable material, look up values for maximum stress, figure in a safety factor for material variation, and arrive at a number predicting safe bending allowance for your particular cable. But unless you gain masochistic pleasure from second-order differential equations, I recommend something simpler: the 8X rule. For any electrical cable, multiply the overall diameter of the cable by eight, and use that as your minimum bend radius. Of course, there are exceptions for shielded cables and multi-core shields, but this basic rule is accepted by the National Electric Code, and will get you the relief you need, without adding the cable’s stress to your own. Okay, so now we know why we need strain relief, what strain relief is, and even how tight to make the bends. Can we simplify incorporating it into the design and get a shakennot-stirred order on the way? Yes! is subject to common pulling forces. One of the great things about this design is its classic look, so this makes it a great option for cables in high-end consumer designs (Fig. 1). Figure 1. Metal strain relief - simple and beautiful Plastic Designs Much more common these days are strain relief designs made of flexible plastic. While there are theoretically an infinite number of designs, most designs fall into one of three categories: one-direction, multi-direction and solid. 1. One-Direction Strain Relief No, we are not talking about using upbeat music to relax. But properly designed, this design is something to sing about. (Almost. Well, not really. Who sings about electrical designs. COMMON STRAIN RELIEF DESIGNS Strain on electrical cables has been around as long as humans have been channeling electricity for our own devious uses, and electrical strain relief designs have been around nearly as long. Today there are several common designs, each with some pros and cons. Metal Strain Relief Older designs involved the use of a metal spring surrounding the cable at the cable-connector junction. Simple and effective, just make certain when incorporating the springs into your design that the bend radius will be large enough when the cable ‍Figure 2. One-direction strain relief is great for relatively predictable applications Uni-directional designs give bend relief in one direction while remaining stiff in the other (Fig. 2). A series _____________ Continued on page 40