How to connect the four wires of the three-phase motor of the water pump control distribution box?

The connection method of the four wires of the three-phase motor in the water pump control

 distribution box is as follows:

Wiring inside the Distribution Box

- **Power Incoming Line**: For the three-phase four-wire power incoming line, the three phase wires 

(generally yellow, green, and red) are respectively connected to the three incoming terminals of the 

main switch inside the distribution box, and the neutral wire (generally blue) is connected to the 

neutral wire terminal block beside the main switch.

- **Contactor Wiring**: Three phase wires are led out from the outgoing terminals of the main switch

 and respectively connected to the incoming terminals of the three main contacts of the contactor. 

The outgoing terminals of the three main contacts of the contactor are then respectively connected to

 the three incoming terminals of the thermal relay.

- **Thermal Relay Wiring**: The three outgoing terminals of the thermal relay are connected to the 

three terminals inside the motor junction box to supply three-phase power to the motor. The thermal 

relay also needs to be connected with a control wire, which is generally led out from the normally closed 

contact of the thermal relay and connected to the control circuit. This is used to cut off the control 

circuit when the motor is overloaded, release the contactor, and thus protect the motor.

- **Neutral Wire Wiring**: A neutral wire is led out from the neutral wire terminal block inside the

 distribution box and connected to the neutral wire terminal inside the motor junction box. If the 

motor is connected in a star connection method, the neutral wire is connected to the neutral point 

of the motor winding; if the motor is connected in a delta connection method, the neutral wire is 

generally not connected to the motor winding but is used as a protective neutral connection and 

connected to the outer casing of the motor to ensure safety.

Wiring inside the Motor Junction Box

- Open the motor junction box and find the six terminals of the motor, which are generally marked 

as U1, V1, W1, U2, V2, and W2.

- If the motor is connected in a star connection method, short-circuit the three terminals U2, V2, and 

W2 together. The three terminals U1, V1, and W1 are respectively connected to the three phase wires

 led from the outgoing terminals of the thermal relay of the distribution box, and the neutral wire is 

connected to the neutral point of the motor (i.e., the common point of the short-circuited U2, V2, and W2).

- If the motor is connected in a delta connection method, connect U1 and W2, V1 and U2, W1 and V2 

respectively with connection pieces. Then, the three terminals U1, V1, and W1 are respectively connected 

to the three phase wires led from the outgoing terminals of the thermal relay of the distribution box, and

 the neutral wire is connected to the grounding bolt of the outer casing of the motor.

    When wiring, ensure that the connections are firm to avoid loosening. At the same time, pay attention

 to distinguishing between phase wires and neutral wires to avoid wrong connections. After the wiring is 

completed, an insulation test should be carried out. Only when the insulation is in good condition can the

 power be turned on for operation. If you are not familiar with electrical knowledge, it is recommended 

that a professional electrician carry out the wiring operation to ensure safety.