When a protection function trips on the CMC-MX series built-in bypass soft starter (380 V, 7.5–280 kW), the unit shuts down immediately and the display shows the active fault. Use the code below to identify the cause and apply the matching remedy before resetting.
CMC-MX Fault Code Table
Display | Status description | Remedy |
STOP | Start signal given, motor does not respond | 1. Check whether terminals 3 and 5 on X1 are closed. 2. Check control circuit wiring and the control switch. 3. Check whether control supply voltage is too low. 4. Check parameter C200 setting. |
No display | Unit powers up with nothing on screen | 1. Check whether terminals 6 and 7 on X3 are closed. 2. Check the control supply voltage. |
Err1 | Phase loss during motor starting | Check the phase voltage of all three supply phases; locate and clear the missing phase. |
Err2 | SCR / thyristor overheat | 1. Confirm good ventilation and vertical mounting. 2. Check the heatsink for overheating and whether the over-temperature switch has opened. 3. Starting too frequently — reduce the start frequency. 4. Check low control supply / excessive voltage dip during start. |
Err3 | Start failure | 1. Check every working parameter; verify settings match actual motor data. 2. Start not completed within the C105 time — check whether the current-limit multiplier is set too low. |
Err4 | Input-output short circuit, or open motor connection (C104 = 0) | Short circuit: check for an internal contactor stuck closed; check SCR breakdown or damage. Open connection: verify reliable output-to-motor wiring; check for an open circuit inside the motor; check the SCR; check incoming phase loss. |
Err5 | Current-limit function ineffective, or motor overcurrent during run | Check the C100 setting; check for an output short circuit; investigate sudden load increase or excessive load fluctuation. |
Err6 | Electronic thermal overload | Check for overload operation. |
Err7 | Wrong phase sequence | Check the incoming phase sequence and parameter C103. |
Err8 | Phase current imbalance | Check main-circuit current / voltage balance and parameter C107. |
Err9 | Frequency error | Check mains frequency and parameter C211. |
Err10 | Parameter loss | Power cycle; if the fault reappears, contact the manufacturer. |
Err11 | Wiring error | Check the wiring and parameter C212. |
Fault Reset Procedure
Faults are latched in memory. After clearing the root cause, reset the unit either by holding the STOP key for more than 4 seconds, or through the external fault-clear input (DI multi-function terminal). Reset returns the starter to the start-ready state.
Field reference: for a real commissioning outcome on a fan load, see the case study of a CMC-MX built-in bypass soft starter on process fans at a Zhejiang environmental plant — 350% Ie current limit, 15 s ramp and 40% initial voltage.
