GB 50057-2010 第5.2.10条
**** | The connection between the air termination and the down conductor shall be made by welding or clamp connectors. Welding length: for round steel, double-sided welding shall be not less than **6 times the diameter**, and single-sided welding not less than **12 times the diameter**; for flat steel, the welding length shall be not less than **2 times the width**, with welding on at least three sides.