apparatus for surface treatment by cataphoresis of metal parts particularly of motor vehicle bodies , supplied by direct current . a tank whose sides carry anodes is provided where the treatment occurs . an overhead conveyor is provided which brings the bodies to be treated in swingtrays spaced apart by a regular spacing λ . a carriage or main body equipped with two contact slides mounted on two parallel conductive rails and located above the tank , provide electrical connection to each body . the bodies to be treated effectively becoming the cathodes . the two rails are divided regularly into portions or dividing rails by an insulating material , each portion connected to the negative terminals of rectifiers , supplying the current . each mobile body is always in electrical contact with a divided rail to ensure that no unnecessary cut offs of current occur , thereby preventing coating defects .