Thanks to Alan Belson for the following scans of 1920s lines and equipment.
Attached pic of 1926 UK 11kv terminal transformer pole. This is the dawn of the 'grid' - before this, individual power stations operated close to consumers, so transmission over long distances was unnecessary.
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Two-circuit 11kV lines in 300 ft. spans:
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Design of poles for 400 ft. spans:
Click here for enlarged version ---------------------------------------------------------
66kV poles & lines: