Recommended Cable tensioning
While the cables in your railing shouldn’t be tight to the point where they bend your rails or posts, they absolutely cannot be too loose. Loose, sagging cables have poor atheistic qualities, but more importantly, they’re not up to cable railing code requirements. International residential codes specify that a four-inch diameter sphere shouldn’t be able to pass between vertical or horizontal cables. This is for safety reasons, preventing small heads and shoulders from being able to squeeze through the space. Loose cables let children stretch them and widen the space between cables to crawl or stick their head through. Even if no children are in the home, maintaining enough tension to prevent cables from moving or stretching is still a requirement to pass a building inspection.
Both wood and steel are popular materials for cable railing frames, and they require slightly different tensions. While wood has some flexibility to return to its original shape and position if you bend it through over tightening, wood’s strength is also a universal—and pretty measly—335 pounds per square inch. This force load that you can easily exceed with a tensioner and a wrench, which means that wood can be broken as easily as it is bent. Metals are stronger, with stainless steel tubing able to carry around a 1,000 pounds along a 6- or 8-foot section before yielding. This too can be easily exceed by just being overenthusiastic when tightening the tensioner.
While codes specify that cables should be tight enough that they cannot be stretched apart to allow an object through, there is no single set standard for how tight cable railings should be. There are way too many different manufacturers of cables and cable railings, and too many types of frames to definitively say. Estimates of the typical tension of a cable railing range from 100 to 200 pounds of force, but there are even higher estimates out there. Five hundred pounds of force is stated fairly often, and 1,000 pounds has been mentioned as a goal. Since wood’s reliable safety rating is about 335 pounds per square inch, this is cause for some concern, and would suggest proceeding with caution when creating a wood-framed cable railing.
We suggest that if you’re building your cable railing system, you’ll want to aim for 100 to 150 pounds of force. That’s tight enough to prevent your cables from being deflected without stressing the frames. We have partnered with Loos and Company in offering their PT-1 Tension Gauges which offers ±5% accuracy in real time while tensioning the cables.