(1) The three-phase asynchronous motor does not need to be connected to the neutral line, because the sum of vectors of three-phase electricity is zero at any time. Even if the zero line is connected, there is no current, so there is no zero line for three-phase motor, so there is no need to connect the zero line.
(2) The reason why there is no zero line for three-phase motors is that the voltage between the zero line and the phase line is 220V, while the voltage required for three-phase asynchronous motors is 380V, so three-phase motors need to be connected to three-phase power lines without a zero line.
(3) The purpose of enclosure grounding is to prevent electric shock accidents caused by electrification of enclosure due to insulation damage of some phases.
(4) However, it is recommended not to use the same inverter grounding wire as the motor grounding wire, because the grounding wire may be aged and broken for a long time in some factory environments with heavy moisture.
(5) In TN-S system, the metal shell of electrical equipment such as motor should be grounded, that is, PE wire! A power supply system cannot be grounded and connected to the neutral line again! At the end of TN-S system, the voltage difference between the zero line and the ground line may reach 10 volts or even higher due to three-phase imbalance and third harmonic.
(6) The connection methods of three-phase asynchronous motor include delta connection and star connection. △ refers to the triangle connection method, that is, short circuit the upper and lower opposite terminals in the junction box to obtain three pairs of electrodes, and then connect the three-phase live wires respectively. Y means star connection, that is, short circuit the upper three terminals in the junction box, and connect the lower three terminals to the live wires respectively.