General Order 64-A
Definitions Of Terms Used In This Order
23.1 Voltage (or Volts) means
the highest effective voltage between any two conductors of the circuit
concerned except that in grounded multi-wire circuits, not exceeding 750 volts
between outer conductors, it means the highest effective voltage between any
wire of the circuit and the ground.
In underground circuits not exceeding 750 volts, voltage to ground means the voltage of the circuit.
When one circuit is directly connected to another circuit of higher voltage (as in the case of an auto transformer) both are considered as of the higher voltage unless the circuit of the lower voltage is effectively grounded from connection merely through electromagnetic or electrostatic induction.