A mode of protection is the measurement between two protected electrical points. A 4-Mode product usually refers to the following paths L123-Neutral and Neutral to Ground. A 7-Mode product introduces a path between each Line and Ground, therefore; L1,2,3-Neutral, L1,2,3-Ground and Neutral –Ground. Some manufactures include the Line-Line paths, this adds an additional three modes to the equation. There are several white papers in the Leviton’s technical library discussing the disadvantages to a 10/All mode system.