Delta MS300 oc overcurrent fault: what to check

• During acceleration: a ramp too fast for the inertia or for the torque the machine needs to start.
• During deceleration: a stopping ramp that is too short.
• At steady speed: a sudden load change, something jammed or material built up in the machine.
• A short circuit between output phases or to ground, often from damaged cable or moisture in the motor terminal box.
• A motor undersized for the job, or motor parameters loaded incorrectly in the drive.

1. 1Write down the exact variant shown on the display. Accelerating, decelerating and steady running are solved in different ways.
2. 2Remove power, apply lockout/tagout and wait for the bus to discharge. Then disconnect the motor and measure insulation between phases and to ground: that rules out a short circuit, the only urgent item on the list.
3. 3Turn the shaft by hand if the machine allows it. A seized bearing or jammed material is found in thirty seconds and explains many steady-state overcurrents.
4. 4If insulation is fine and the mechanics turn freely, lengthen the ramp that matches the variant and test again.
5. 5Check the motor nameplate data loaded in the drive. A wrongly parameterized motor forces currents the drive reads as a fault.

Work on an energized panel: apply lockout/tagout and follow your plant procedure. This sheet guides the diagnosis, it does not replace it, and the manufacturer manual overrides anything written here.