Introduction

In many industrial setups, an SCR power controller may trigger an inrush current alarm (INRUSH) during startup—even when the load is not overloaded.

👉 Key difference:

• Overload → current exceeds rating during operation
• Inrush current → short peak current at startup (milliseconds)

📍 Even a very short current spike can trigger protection.

First Check: Confirm It’s Not a Real Fault

Before adjusting anything, verify these two points:

1. Check actual current behavior

• Measure startup peak current
• Compare with stable running current

✔ If only startup peak is high → normal inrush
✔ If running current is also high → real overload

📍 Always distinguish peak vs continuous current.

2. Check measurement circuit

• Inspect current sensor / CT / sampling resistor
• Look for unstable or abnormal readings

📍 Faulty detection may cause false alarms.

Method 1: Adjust Inrush Protection Settings

This is the fastest and most effective solution.

Key parameters:

• Inrush current threshold (INRUSH LEVEL)
• Inrush delay time (INRUSH DELAY)

Recommended adjustment:

• Resistive load → 2.5–3× rated current
• Inductive load → 3–4×
• Capacitive load → 4–5×
• Delay time → increase to 0.3–0.5 s

📍 Allow short peaks without triggering protection.

Method 2: Use Soft Start or Ramp Control

Changing startup mode can significantly reduce current spikes.

Options:

• Soft start → gradual voltage increase
• Ramp start → controlled rise slope
• Constant current start → limit startup current

📍 Smooth startup = lower peak current.

✔ Recommended:

• 3–5 seconds soft start for most loads
• Longer for high inertia systems

Method 3: Add External Hardware Protection

For high-power or sensitive loads, settings alone may not be enough.

Solutions:

• Series reactor (choke) → limits current surge
• Soft starter (for motors) → controlled startup
• Staged heating (resistive loads) → avoid full load startup

📍 Hardware buffering is essential for large loads.

Method 4: Improve Power Supply & Wiring

External factors can amplify inrush current.

Check:

• Voltage stability (avoid sudden drops)
• Tight terminal connections
• Proper cable size
• Correct phase sequence (3-phase systems)

📍 Poor wiring or unstable supply increases current spikes.

Quick Verification

1. Start the system and check if alarm disappears
2. Measure startup peak current
3. Ensure stable operation without overheating

📍 If peak is controlled and system runs stable → issue resolved.

Conclusion

Inrush current alarms without overload are usually caused by:

• Improper protection settings
• Unsuitable startup mode
• Lack of buffering
• External electrical issues

👉 Follow this order:

1. Adjust parameters
2. Optimize startup method
3. Add hardware if needed
4. Improve power and wiring

📍 Matching startup behavior to load characteristics is the key to eliminating inrush alarms.