Lightning Plays the Stadium

This article highlights proper electrical grounding when roof structures have no fixed connections to the ground. The roof’s mechanization designers, at Uni-Systems Inc. in Minneapolis, decided to study the effects of an electrical impulse through a machine-bearing surface. Uni-Systems had been confident that implementing conventional copper shunt grounding to bypass the nonconductive points would solve one problem. However, once the path was shunted, current was routed to the wheels and bearings. Testing would be required to identify the effects of a lightning strike in a greased bearing. Uni-Systems returned to Neetrac to test a new assembly, consisting of a plain spherical bearing with fibriloid liner, an axle, and spacers, installed to an eye bracket machined to house the bearing and a clevis bracket. The tests showed that with shunt wires installed, a current with up to 20,000 amperes passing through the hinge has no adverse effect—either short or long term—on the hinge bearing. Thus, the hinge bearing assembly can be used as a part of the grounding path for lightning protection.