Optical attached cable (OPAC) is a type of fibre-optic cable that is installed by being attached to a host conductor along overhead power lines. Deploying fiber above ground on poles or towers removes the need for underground digging and is particularly useful when the ground is uneven, rocky or both. Generally speaking, they are usually made of heavy jackets and strong metal or aramid. OPGW (Optical Ground Wire): This is an all-metal cable that holds a large number of optical fibers inside. These overhead cables are used in power lines to both transmit data and protect against lightning strikes.