A three phase load requires a minimum of:

In a three-phase electrical system, the load is designed to operate effectively with three separate phases. Each of these phases carries an alternating current that is sinusoidal and phase-shifted by 120 degrees, which allows for a more efficient and balanced distribution of electrical power.

Having three supply lines ensures that each phase can deliver power to the load simultaneously, distributing the electrical demand evenly. This is crucial for the operation of three-phase motors and other equipment, as it provides a constant and reliable source of power.

Using just two supply lines would not provide the necessary three-phase power configuration, and insufficient or uneven phases could lead to inefficiencies, increased energy loss, or even mechanical failure in equipment designed for three-phase operation. Four supply lines typically include an additional neutral line in a three-phase system, which isn't required for basic three-phase power but may be included for specific balancing needs or single-phase loads. A single supply line would not suffice for three-phase loads, as there would be no way to harness the benefits of three-phase power. Thus, using three supply lines is fundamental for the correct operation of three-phase systems.