A rubber grommet provides local edge protection where an intact wire or cable passes through a panel. It does not restore insulation that has deteriorated or been damaged.
Address damaged wiring before use rather than covering it with a grommet. For an intact cable, match the opening, panel thickness and passage dimensions and ensure suitable support and bend clearance.
A basic grommet is not a universal cable clamp or water seal. Specify those functions separately if needed. Select the compound for the service environment and verify that installation has not cut, pinched or displaced the rubber or cable.
