Final answer:
A three-phase transmission system requires only one-third the total weight of conductor when compared to a single or two-phase system.
Step-by-step explanation:
A three-phase transmission system requires only one-third the total weight of conductor required for a single or two-phase system. The efficiency of a three-phase system is due to the way the three phases are able to share the total power across the conductors more evenly, reducing the need for more material while maintaining the same power transmission capabilities.