A bushing és an aïllant dispositiu que presenta a live conductor into an elèctric dispositiu o through a wall. The former is called an electrical sleeve, and the latter is called a wall sleeve. Casing is usually used in building basements, that is used to protect pipes o facilite pipe installation. The classification of casing includes rigid casing, flexible waterproof casing, steel pipe pipe casing carcassa i ferro carcassa.