Shorted Thyristor or Wrong Connection

What does SSCr mean?

One or more thyristors within the soft starter have been detected as shorted, or an incorrect motor connection has been identified. This fault prevents proper current control and can lead to uncontrolled motor operation or damage.

• Internal short-circuit within one or more thyristor switching devices due to overvoltage, overcurrent, or component aging.
• Incorrect motor phase connection to the soft starter's output terminals (e.g., phases L1/T1, L2/T2, L3/T3 are miswired).
• Short circuit within the motor windings or motor cable insulation breakdown leading to current imbalance.
• Input phase voltage imbalance or transient spikes exceeding thyristor voltage ratings.
• Damage to the soft starter's gate drive circuit responsible for controlling the thyristors.

Click steps to track your progress.

1. 1

   1. Disconnect motor cables from the soft starter's output terminals (T1, T2, T3) and measure resistance across each soft starter output phase using a multimeter to check for internal shorts.

2. 2

   2. Visually inspect the soft starter's power circuit board for signs of arcing, burning, or component damage (e.g., thyristor module, gate drive resistors).

3. 3

   3. Verify motor winding resistance and insulation resistance (Megger test) to ground and phase-to-phase to confirm motor integrity.

4. 4

   4. Confirm correct motor cable connections to the soft starter's T1, T2, T3 terminals and input power connections to L1, L2, L3.

5. 5

   5. Measure incoming line voltage balance at L1, L2, L3 terminals and check for voltage transients with a power quality analyzer.