ALLPCB
Overview
Electric motors commonly use two wiring methods: delta and star. Motors with a star connection are typically small motors below 3.0 kW. Star-connected small motors impose a smaller voltage disturbance on the power grid at startup, so small motors are often wired in a star configuration. Characteristic: low power, high torque.
For larger motors, reduced-voltage starting methods are used to avoid excessive voltage disturbance to the supply and to reduce stress and wear on the motor windings and insulation during startup. Star-delta (Y-Δ) reduced-voltage starting is one common method.
Star (Y) Connection
In a star connection, the six terminals of the motor windings are arranged so each of the three phases has a clear start and end. The end terminals of the three phase windings are connected together to form the neutral point. The start terminals of the three-phase windings serve as the external terminals for connection to the power supply.
Delta (Δ) Connection
In a delta connection, the six winding terminals are grouped into three phases, with each phase's start connected to the end of another phase to form a closed triangle. Once each phase start and end are connected, the three corner points of the triangle serve as the terminals for connection to the power supply.
Field Note
In one case, a technician wired a 2.2 kW motor but the motor did not run after closing the breaker. Normally a connected motor will exhibit at least some sound even when not running, but this motor produced no sound. Inspection of the motor junction box revealed the six winding terminals were isolated and there were no jumper links to form a star or delta connection. After installing three jumper links and wiring the motor in a star configuration, the motor ran normally. This illustrates the importance of ongoing training and skills updating for electricians as electrical equipment evolves.
