Why output voltage is present at the output terminal of ATS48 when motor is not connected and it is on Rdy state.

Even when the ATS48 soft starter is in the OFF state and the motor is disconnected, a residual voltage may still be observed at the output terminals. This is normal behavior and occurs due to the internal design of the starter.

⚙️ Technical Explanation:

• Inside the ATS48, thyristors are used to control power to the motor.
• In parallel with each thyristor, an RC snubber circuit (a resistor and capacitor combination) is installed.
• These RC circuits are used to assist with thyristor commutation and to protect against voltage spikes.

⚡ Why Residual Voltage Appears:

• Even when the thyristors are not conducting (i.e., not triggered), the RC snubber circuits allow a small leakage current to pass through.
• This results in a residual voltage being present at the output terminals.
• This voltage is not capable of driving a motor but can be measured with a voltmeter or seen on sensitive equipment.

📌 Important Note:

• This residual voltage is not a fault and does not indicate a malfunction.
• However, it’s good practice to isolate the starter completely before performing any maintenance or testing.

Released for: Schneider Electric India