Anyone who has felt a tingle of electric current when touching a wall socket or a badly grounded appliance isn’t eager to repeat the experience. After all, the next time it could be fatal. Stray currents and excessive voltages—the same phenomena that are potentially dangerous to human beings—can also damage equipment, especially electronic controls, which are extremely sensitive to overcurrents and overvoltages. Even when these conditions don’t cause permanent damage, they can interfere with electronic signals and cause equipment to malfunction.