Hello Mr South Park again,
Still can not answer your question but you may recall my saying a couple of things here.
One, I suggested that maybe the one wire was not for telegraph but for electricity wire.
Two, I mentioned power being supplied to the Como depot for lights powered from the roundhouse.
And three, I talked about the shed that was later turned into a garage behind the depot being the battery room.
Here are two photos of the back of the depot that seem to show the same type glass insulators that you also show. They are in the middle of the back of the office. Ceramic insulators are on each corner too.