Cable joints
Ahh is that what it looks like up close, never seen one as they are hidden underground here with one at each 100 meters.
There are quite a few versions of cable joints we can use, it would generally depend on the cable sizes and/or where the joint is to be sited ?. If it's to go behind the pole capping (that metal thingy at the bottom of the pole), then it would have to be an 'in-line' heat-shrink closure. Above the capping, we can use whatever we feel would be best suited ??.
For obvious reasons, the mechanical range of joints are preferred by the engineer, as they are very easy to open and close, compared to the heat-shrink versions.
Why they are actually on the pole could be for a variety of reasons. In certain areas, we get the mad axe-man who thinks it great to go around chopping our cables. It's far easier and quicker to re-joint the cable, than to run a new one from the nearest underground box to the top of the pole. In these areas, you won't be surprised to see 2 sets of metal capping's fixed to the pole to cover the cable to a greater height.
Another reason could be that a new DP or CP (Telegraph poles) is required, and the planner will request that the 'Spare pairs' that are available at a nearby existing DP, are diverted to the new pole via an overhead aerial cable. The new aerial cable would then have to terminate in a joint on the existing DP to 'Pick up' the spare pairs. Hope that makes sense ??