Electric lighting service lines most likely were strung upon the upper two crossarms in this image. The single arm below would have been for telephone subscriber lines. Note the small transformer on the pole in the foreground. Typically transformers were mounted atop utility poles with their higher voltage circuits in nearby proximity. Perhaps this one was installed this way for easier servicing or on account of physical constraints up where the electricity wires are. Of course, my former assumptions would be incorrect if the phone lines were on top and the electric lighting wires lowermost...