Most lightning strikes are not direct, but rather induced surges in power lines or the result of one of the branches of the main strike. There is nothing that will protect equipment from a direct strike -- the energy level is just too great. And, the gap in a knife switch is no challenge to the strike. I should point out that the gap is not the distance from the blade to the seat, but the distance across the insulation in the mounting hardware which is probably good for a few thousand volts and not millions of volts. Direct strikes on homes are very rare, but I saw what can happen when a friend's home was hit by a direct strike. It not only melted all of the wiring in the home, breaker panel, outlets, fixtures, appliance motors, telephone, televisions, stereo, computers anything else electronic. It also did other major damage such as melting all of the gutters around the house, knocked a six foot hole in one of the bedroom walls where the direct strike occurred, and jumped to the gas meter just outside of the blast hole. The strike blew the gas line in two and ignited the gas that was coming out of the broken line at the meter producing a flame about 4 feet long sort of like a giant sized propane torch. Fortunately, the flame did not ignite anything before they were able to shut off the gas valve which fortunately still worked. Unplugging a lathe with a VFD in such a situation probably would save the motor, but the electronics might not survive the EMP.
Bill
