What type of construction consists of 3 phases without a common neutral wire?

Delta construction is characterized by its three-phase system where the ends of each phase winding are connected in a closed-loop configuration, forming a triangle or delta shape. This type of construction does not use a common neutral wire because each phase carries the full line voltage and the phases are interconnected through the windings.

In delta systems, the phase currents are out of phase with one another by 120 degrees, allowing for a balanced distribution of load. The absence of a neutral wire means that all current returns through the phases themselves, which can enhance efficiency in certain applications, particularly in industrial settings where large motors and heavy machinery are prevalent.

Wye construction, in contrast, does utilize a neutral wire, allowing it to balance single-phase loads more effectively. Single-phase construction only involves one phase and does not provide the benefits of three-phase power. While triple-phase construction sounds similar to delta, it does not specify the connection configuration. Therefore, delta construction is clearly distinct for its lack of a neutral and its specific triangular connection setup, making it the correct answer.