Applicable Systems
SIVACON S8
Symptoms
The 3VA molded-case circuit breaker trips with the I (instantaneous) indicator displayed. The LED on the electronic trip unit flashes red. The downstream motor stops abruptly.
Possible Causes
- Motor starting current exceeds the instantaneous pick-up setting
- Phase-to-phase short in the motor cable or terminal box
- Breaker instantaneous setting too close to motor locked-rotor current
- Damaged contactor contacts welding shut and causing sustained overload
Troubleshooting Steps
- Step 1: Check the motor locked-rotor current (typically 6-8x FLA) and compare with breaker instantaneous setting
Breaker instantaneous is set >12x motor FLA or per IEC 60947-2 coordination tables - Step 2: Megger the motor and cable at 1000V DC to detect insulation faults
Insulation resistance is >5 MOhm phase-to-ground and phase-to-phase - Step 3: Inspect the contactor contacts for welding or excessive erosion
Contacts move freely, no welding, and contact gap is within manufacturer spec - Step 4: Verify the cable sizing meets the breaker ampacity and motor FLA requirements
Cable ampacity exceeds breaker rating per IEC 60364-5-52
How to Reset
Reset the 3VA breaker by pressing the ON button after the red trip indicator is reset. Ensure the cause is eliminated before reclosing.
Common Replacement Parts
- 3VA1112-5EF32-0AA0: Siemens 3VA12 circuit breaker with ETU320 (Verify frame size and trip unit compatibility with the existing breaker)
Frequently Asked Questions
- Q: What does the I trip indicator mean?
It indicates an instantaneous overcurrent trip, typically due to a short circuit or severe overload exceeding the magnetic pick-up threshold.
- Q: How do I adjust the instantaneous setting?
Use the rotary dial on the ETU trip unit. Settings are usually 2x, 3x, 4x, 6x, 8x, 10x, 12x, 15x In.
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Source: Siemens SIVACON S8 Operating Instructions, Edition 10/2023
Category: Electrical
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