Soft Starter Wiring Diagram and Connection Procedure

A starter is a very important device to protect a motor from effective damage. We know that an electric motor can draw an excessive current during its starting if it is used without a motor starter. This high inrush current at the starting time may damage the motor and even it can affect the power system also such as power fluctuation, voltage drop, etc. So most of the motors are always operated with a motor starter especially the high-power motor must be operated with motor starter. There are so many types of motor starters available in the market. A soft starter is the latest and most advanced type of motor starter that is used for high-power motors(more than 10HP motor).

There are a lot of advantages of a soft starter over a normal conventional starter such as,

• Soft Starter can handle very high-power motors
• The operation speed of the soft starter is faster.
• As it is built with semiconductor devices so the electrical power loss is much less
• Soft starters require very few user adjustments they can operate automatically.
• It provides a very smoother startup than other starters.
• Soft starters require very less maintenance.

Soft Starter Wiring Diagram

Here, you can see the wiring diagram of soft starter.

In the above wiring diagram, you can see the three-phase soft starter has an incoming terminal in the upper section and outgoing terminals in the downside. Also, you can see a bypass contactor is also connected in parallel with the soft starter. Nowadays there are soft starters are available in the market that do not need an additional bypass contactor. The bypass contactor is already built with the motor starter.

Anyway, let's know the working principle of this starter. First of all when the motor is turned On the soft starter gradually increases voltage and current. So the high inrush current flow during the starting got eliminated. Once the motor runs at full speed and full load current, the soft starter activates the bypass contactor so the motor will be directly connected to the main power supply. And during this full-load operation, the soft starter has no control over the motor. Now, when we stop the motor the bypass contactor will be turned off and the motor will be connected to the soft starter. And the soft starter will prevent the instant stopping, it will gradually decrease the voltage and current so the motor will stop smoothly.

You can see here we used an MCCB as the main switch, you can use anything according to your electrical system.

Soft Starter Connection Procedure

As there are different models from different manufacturers. So it is better to read the manual and guidebooks before making the connection. Here, the procedure for the general connection is applied to most of the soft starters available in the market.

• Connect the incoming power supplies at the top side as shown in the figure.
• Connect the outgoing terminals at the bottom side. Must check the identification on the soft starter for an incoming and outgoing connection.
• Connect the bypass contactor in parallel to the soft starter with the main power supply and load.
• Find out the bypass output terminal on the soft started and connect the contactor coil terminals to the bypass output of the starter. Generally, it is a Normally Open(NO) terminal.

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