How to connect a three-phase motor?

How to connect a three-phase motor?

One of your pieces of equipment is fitted with a three-phase motor which is starting to show signs of wear? Do you want to install or replace an electric motor on a pump, a fan, a compressor, or a machine tool?

Are you wondering how to connect a three-phase motor? Don't panic, we will explain everything to you!

Let's start at the beginning. Why use three-phase voltage rather than single-phase voltage? It's both simple and logical. The difference between a three-phase supply and a single-phase supply is easily distinguished. Three-phase voltage powers your electric motor with three phases and an earth, unlike single-phase power which uses only one phase, one neutral, and the earth.

Three-phase motors are generally supplied by a power and control circuit, by a variable frequency drive, by a soft starter, or by a star/delta starter.

But why use three-phase voltage? Industrialists generally use three-phase voltage because it allows them to reduce the current consumed by their motors. Three-phase electrical networks provide 400V, so the absorbed current is lower in three-phase because the absorbed current of a three-phase electric motor is equal to the useful power, divided by the voltage.

• Example: I = P / ( U x √3 x cos phi )

The higher your supply voltage, the higher the current consumed by your motor. In some cases, there are still 230V three-phase supplies, however, they are becoming increasingly rare.

Returning to the connection of your three-phase electric motor, it is relatively simple, however, a few principles must be respected so as not to damage your motor, injure yourself, or cause your installation to fail.

First step: know the supply voltage of your motor.

A three-phase motor can be offered in 230/400V three-phase voltage and 400/690V three-phase voltage. We regularly find small power motors wound in 230/400V three-phase and higher power motors in 400/690V.

The first step is to know the supply voltage of your three-phase motor. This will allow you to know how to connect your three-phase motor. In France, there are two types of three-phase voltages. 230V and 400V three-phase voltage.

In most cases, your supply voltage is 400V three-phase, however, it can sometimes happen, in old installations, to have a 230V three-phase voltage.

To measure the supply voltage, you need to equip yourself with a voltmeter or a multimeter that delivers a result in Volts "U". Please note, this operation must be carried out by an authorized person because it can be dangerous.

Once this step is completed, you know your supply voltage. This information will allow you to determine the appropriate coupling for your motor.

2nd step, Select the appropriate coupling for your three-phase motor.

As we have just seen, your three-phase motor can be 230/400V three-phase or 400/690V three-phase. This information is readable on the nameplate of your three-phase motor. This information is essential to know how to connect a three-phase motor. Feel free to read our article that allows you to understand the information on a motor nameplate

Discover the different possible couplings.

• Your network voltage is 230V three-phase and you have a 230/400V three-phase motor. Your coupling must be in delta.
• Your network voltage is 400V three-phase and the voltage indicated on your nameplate is 230/400V. The coupling of your three-phase motor must be in star.
• Your network voltage is 400V three-phase and you have a three-phase motor where the voltage indicated on the nameplate is 230/400V, your coupling must be in star.
• Your network voltage is 400V three-phase and you have a 400/690V three-phase motor, the coupling of your electric motor must be in delta.

Please note, it is possible to find two-speed electric motors or star/delta start. In this case, no coupling bar should be used to power your electric motor. There are electric motors with separate windings and Dahlander motors.

Last step, check the proper functioning of your three-phase motor.

Congratulations, your three-phase motor is working. It is rotating in the right direction and your application is running like clockwork. However, we advise you to measure some information.

First, measure the voltage under load. This allows you to know if you do not have a voltage drop related to an electrical problem or a cable section that is too small. Also, check the currents under load, this will be an opportunity to be sure of the proper functioning of the motor. Too high a current can be caused by an overload or a mechanical hard spot. This type of operation is necessary to ensure the reliability of your equipment.

Still in doubt? Our technical team remains at your disposal.