Countryman, most (all?) modern cables have a strength member inside them, either something like nylon pull cord, or the plasticy separator that goes down the middle. This helps a lot in terms of protecting the wires inside when you pull on the cable. There will be a vendor defined pull tension limit, which is usually pretty reasonable. Basically, be reasonable and you're fine. Don't yank with all your might. Make very sure you are feeding the cable *gently* around bends and dealing with snags gently, not by just pulsing hard pulls.