- Work at height training shall be provided to staff. This publication is intended as a practical guide for the proper and safe* installation of cable ladder systems, cable tray systems, channel support systems and associated supports. If a tray is overloaded, corroded, poorly supported, or contains live cables, it can create severe risks for workers and equipment. 305(a)(3), or comparable standards promulgated by States. us-trations without notice. The mechanical and electrical characteristics, tests, certifications, overall quality management, recommendations mentioned. - Obtain PTW before the start of the activity.