Lub bushing yog ib qho khoom siv insulating uas qhia txog tus neeg xyuas pib nyob rau hauv ib qho khoom siv hluav taws xob lossis los ntawm phab ntsa. Lub qub yog hu ua lub tes tsho hluav taws xob, thiab tom kawg yog hu ua lub tes tsho phab ntsa. Casing feem ntau yog siv rau hauv lub tsev hauv qab daus, uas yog siv los tiv thaiv cov kav dej los yog pab txhawb kev txhim kho cov yeeb nkab. Kev faib tawm ntawm cov casing muaj xws li tawv casing, hloov tau yooj yim waterproof casing, steel yeeb nkab casing thiab hlau casing.