Is a Line Contactor Mandatory for Altistart Soft Starters ATS22, ATS430, ATS480, ATS490?

A line contactor or another independent isolation device is required when using:

• Altistart 22 Soft Starter (ATS22)
• Altistart 430 Process Soft Starter (ATS430)
• Altistart 480 Process Soft Starter (ATS480)

A line contactor is not mandatory for the Altistart 490 Process Soft Starter (ATS490) because the product includes an integrated safety function designed to safely stop the motor.

Why is an external isolation device required for ATS22, ATS430, and ATS480?

If the power thyristors inside the soft starter become short-circuited, or if the bypass relay in the Altistart 22 remains welded or stuck in the closed position, the soft starter can detect the fault but may no longer be able to stop the motor.

In such a condition, the motor could continue running even after a stop command is issued through a control input, PLC, or another control system. This represents a potentially hazardous situation.

The soft starter can indicate the fault through its fault relay, but it cannot physically disconnect power from the motor. Therefore, an independent device must be used to remove power from the motor circuit when a fault is detected.

Which devices can be used?

The protective device does not have to be a line contactor. Other suitable solutions include:

• Circuit breaker with undervoltage release (shunt trip or undervoltage trip)
• Safety contactor
• Other certified switching devices capable of disconnecting motor power

A typical implementation is:

1. The soft starter detects an internal fault.
2. The fault relay changes state.
3. The fault signal causes the external protective device to trip.
4. Power to the motor is removed, ensuring the motor stops safely.

ATS490 Exception

The Altistart 490 Process Soft Starter incorporates an integrated safety architecture that enables safe motor stopping without requiring an external line contactor solely for this purpose. However, additional switching or isolation devices may still be required to meet local regulations, machine safety requirements, or application-specific standards.