An example of telephone history.
At one time open wire was the media for phone and telegraph lines. The wire is gone and some of the insulators and supports are missing but this is a collection of pictures of these lines as seen just off Grantley Street in York PA. These poles parallel a railroad and were used to support the power, phone and telegraph lines.
Picture by Author
This pole is interesting for a couple reasons. First, the pole itself is relatively rough with the limbs of the tree it was cut from visible. Most of the insulators are missing. They have either fallen off or more likely they are victims of target shooting. The guy wire hangs lamely because the pull of the wire in the other direction is missing. Another sign of deterioration can be seen on the left end of the lower crossbar. The peg that supports the insulator has come loose and fallen through. These are slightly tapered so they go in the hole and are tight. Some of the pegs have been exposed to the weather enough that they are showing signs of deterioration. These are actually threaded wooden bolt that the insulator screws on.
Picture by Author
This shows a crossbar with four intact insulators. These pieces of glass sell for five to twenty dollars today. The wire that was strung on them was 104 to 165 mils hard drawn copper. I wasn’t sure of the size but I know the wire looked heavy from the ground and it had to span about 500 feet and support itself in wind and ice. An article in Chapter 18 of Insulators http://www.insulators.info/articles/openwire/ shows the wire size for telephone on this as 104, 128 or 165 mils. In some other articles it is just listed as 104, 128 or 165 wire so the mils measurement rather than wire gage was the norm. I compared mils to wire gage and found #10 is 101 mills and #6 is 162 mils. If we want to look at it standard house wiring which is mainly #14 and #12 they are 64 and 80 mills respectively. Number 6 is double the DIAMETER of #12 and thus contains four times the copper. A comparison of #10 to #22 which is the largest wire in a standard cable of today, #22 is 25 mils compared to the 101 mils of #10. The diameter ratio is 1:4 with the area and the amount of copper being 1:16! A mile of telephone wire at #10 takes With copper prices now approaching $3 a pound (this is refined copper, not copper processed into wire which would of course cost more). A cubic foot of copper (550 pounds – $1650) will produce over 16,000 feet of #10 putting the material cost for that wire at about ten cents a foot and it takes two strands of this wire for a phone line. Approximately 16 times the amount of #22 and 40 times the amount of #26 can be made from the same copper.