The star-delta key is a starting method of three-phase electric motors, which uses a key of the same name and it can be manual or automatic, and is interconnected to the motor windings, which must be accessible in 6 terminals. It is fundamental to start with a star-delta key that the motor has the possibility of double voltage connection, that is, at 1350 / 2300V, at 2400 / 4160V or 3800 / 6600V. The motors must have a minimum of six connection terminals.

The star-delta start should be used when the motor torque curve is high enough to ensure acceleration of the machine 8072-a with the reduced current. In the star bond, the conjugate is reduced to 25 to 33% of the starting conjugate and the starting current to 33% of the value of the delta linkage. Because of this, whenever a star-delta starter is required, a motor with high starting torque must be used. Some motors, when required by necessity, are designed to achieve maximum starting torque and are therefore suitable for most starting systems, including star-delta, but the high cost of contactors and / or vacuum circuit breakers makes this type of starting for high voltage motors unfeasible.