Solar racking systems endure wind loads, snow loads and thermal cycling. Insufficient pretension or poor anti-loosening measures cause loosening, corrosion and even structural failure. Correct pretension setting and anti-loosening measures are key to project quality.
Bolt pretension is generally set at 60%-75% of yield strength, controlled by torque method, torque-angle method or tension method. Torque values depend on thread size, material and lubrication; use calibrated torque wrenches on site.
Spring washers, double nuts, thread locker and tension-shear bolts are commonly used. For high-wind areas, double nuts or tension-shear bolts are recommended for stable pretension. Note the effect of lubrication on torque coefficient for hot-dip galvanized parts.
After grid connection, regularly inspect torque at critical nodes, especially after rain or strong wind. Retighten and re-treat any loose connections promptly.
The solar fastener range provides bolt selection and torque advice for racking design and construction.