The number of drill holes is dependent on the height and width of the cable trays. However, with the right technique and tools, you can easily drill a clean and precise hole in galvanized metal. You've got your drill, your bits, and your gloves, but as you approach the metal, you're met with a frustrating reality: your drill bits are slipping and. - The steps for installing cable trays, which include marking, cutting, drilling holes, installing supports, and fixing fittings and accessories.