Motor Does Not Start
Likely Cause
Main contactor not energising, 12V DC control power absent, or RS485 communication failure.
How to Fix
- 1Confirm the MX-3P-SD LED is lit on the SP-3P-SD assembly. If dark, check 12V DC control power supply.
- 2Confirm Online status in the app before issuing start command.
- 3On start, listen for the main contactor click first. If no click: confirm the RS485 command reaches the module (check LED changes state).
- 4Check for an overload relay trip — the reset button on the overload relay section may be raised. Press to reset, wait 60 seconds to cool, and retry.
- 5Confirm three-phase supply at R, S, T input terminals — measure R-S, S-T, R-T voltages. All should be approximately 415V AC.
Motor Starts in Star But Does Not Transition to Delta
Likely Cause
Delta contactor not receiving the signal, transition timer too short, or delta contactor mechanical fault.
How to Fix
- 1Increase the star-delta transition timer by 2–3 seconds and retry: Device Settings → Motor → Star-Delta Timer.
- 2If the timer is adequate: check that the SP-3P-SD DELTA coil terminal is connected to the delta contactor coil inside the assembly. Open the assembly cover and confirm the DELTA output wire connection.
- 3Check for mechanical binding in the delta contactor — press the contactor manually (with mains isolated) to confirm it moves freely.
- 4Inspect the star/delta electrical interlock wiring inside the assembly — the star contactor NC auxiliary contact must open before the delta contactor can close.
- 5If the motor trips on every transition: the current spike at transition is triggering the overload relay — increase the transition timer to let the motor reach higher speed in star before the switch.
Motor Runs in the Wrong Direction
Likely Cause
Phase sequence at motor 6-wire terminal connection is reversed.
How to Fix
- 1Wrong rotation on a star-delta motor is corrected at the motor terminal box — not at the SP-3P-SD supply terminals.
- 2Isolate mains and prove dead at the motor terminal box. Swap U1 and V1 connections at the motor terminal box (or V1 and W1). This reverses the phase sequence seen by the motor windings.
- 3Do NOT swap R and S (or any supply phases) at the SP-3P-SD input terminals — this reverses phase sequence for all other equipment.
- 4Restore mains, retry, and confirm rotation before closing the motor terminal box cover.
Phase-Loss Alarm Triggered
Likely Cause
Supply phase absent, phase sense wires disconnected, or phase imbalance above threshold.
How to Fix
- 1Measure R-S, S-T, and R-T voltages at the SP-3P-SD supply input. Confirm all three are present and approximately equal.
- 2Check MX-3P-SD phase sense wires: R, S, T sense terminals must be connected. Disconnected sense wires cause false alarms.
- 3If all phases present at supply but one sense reading is 0V: trace that sense wire from the SP-3P-SD input terminal to the MX-3P-SD sense terminal — loose crimp or screw terminal.
- 4Intermittent phase-loss alarms: check for loose connections at the supply incomer and at the SP-3P-SD R/S/T input terminals. Tighten all terminal screws to rated torque.
- 5Reset fault latch in app (Device → Reset Fault) after all phases confirmed stable.
Overload Relay Trips During Delta Running
Likely Cause
FLA dial set to star current (too low), motor drawing excess current in delta, or mechanical load fault.
How to Fix
- 1Confirm the overload relay FLA dial is set to the motor nameplate delta FLA (the full-load current at 415V) — not to the star running current, which is approximately 58% of the delta current.
- 2Measure running current on all three phases in delta. Confirm balanced current and within nameplate FLA.
- 3If current is significantly above nameplate FLA: investigate the mechanical load — pump blockage, impeller wear, excessive delivery head, or process load increase.
- 4If current is balanced and within FLA but relay still trips intermittently: check the relay class (should be Class 10 for standard motors, Class 20 for high-inertia applications). Class 10 may nuisance-trip during sustained elevated loads.
- 5Ensure the motor is reaching full speed in delta before taking the running current reading — measuring current during acceleration (immediately after transition) gives falsely high readings.