Yaskawa L1000A Fault oC Overcurrent

Getting the oC fault on your Yaskawa L1000A elevator drive? Learn how to diagnose overcurrent causes like motor insulation failure, short circuits, and mechanical overloads.

 

In the elevator industry, the Yaskawa L1000A is a legendary drive known for its smooth ride and reliability. However, seeing the oC (Overcurrent) fault on the keypad can bring a building's traffic to a standstill. This fault indicates that the drive's output current has exceeded its instantaneous trip level.

Because an overcurrent event can stem from the motor, the wiring, or the drive itself, a systematic approach is required to find the root cause without causing further damage. Here is a human-made guide to troubleshooting the oC fault in your L1000A drive.

1. Inspect Motor Insulation and Health

The most common reason for an oC trip is a breakdown in the motor's internal insulation. If the windings are damaged due to age or previous overheating, electricity "leaks," causing a current spike.

• Perform a Megger Test: Use an insulation resistance tester to check the motor windings. If the resistance to ground is low, the motor has reached its end of life or is severely damaged.
• Physical Inspection: Check for a burnt smell or signs of overheating at the motor housing.
• Remedy: If the insulation is compromised, the motor must be repaired or replaced.

2. Check Motor Cabling and Grounding

A short circuit in the cables between the drive and the motor is a frequent culprit in elevator shafts where cables move or are subjected to vibration.

• Look for Shorts: Inspect the entire length of the motor cables for nicks, abrasions, or crushed sections.
• Check Grounding: Measure the resistance between the motor cables and the ground terminal. Any continuity suggests a grounding problem.
• Remedy: Remove any short circuits found and re-terminate loose wires. Replace the cable if the outer jacket or internal insulation is damaged.

3. Evaluate the Drive Hardware (IGBT Test)

If the motor and cables are healthy, the fault may be inside the Yaskawa L1000A itself. A blown output transistor (IGBT) will cause an immediate oC trip the moment the drive tries to output power.

• The Diode Test: With power OFF and the DC bus discharged, use a multimeter in diode mode to check the output side short circuit. Check between terminals (B1, U, V, W).
• Remedy: If the output transistors are broken, the drive hardware is failed. Contact your Yaskawa representative or an authorized repair center for a power board or unit replacement.

4. Analyze Mechanical Load and Drive Sizing

Is the elevator car physically too heavy for the motor/drive combination? If the current required to move the car exceeds the drive's rated capacity, it will trip on oC.

• Measure Running Current: Use a clamp-on ammeter to measure the actual current flowing into the motor during a run. Compare this to the "Rated Current" on the drive's nameplate.
• Check for Mechanical Jams: Ensure the elevator brakes are releasing fully and that the guide rails are properly lubricated. A "sticky" mechanical system forces the motor to draw more current.
• Remedy: Reduce the load or increase the drive/motor capacity if the application demands more current than the hardware can provide.

5. Adjust Acceleration and Deceleration Ramps

Aggressive programming can sometimes trigger "nuisance" overcurrent trips. If the drive tries to speed up or slow down a heavy elevator car too quickly, the torque demand causes a current surge.

• Ramp Settings: Review your acceleration (C1-01) and deceleration (C1-02) times.
• Remedy: Increase the ramp times (make them longer). This allows the drive to manage the inertia of the car more smoothly, keeping the current within safe limits.

Summary Troubleshooting Checklist

Checkpoint	Action
Motor Windings	Test insulation resistance (Megger).
Cabling	Check for phase-to-phase and phase-to-ground shorts.
Internal IGBTs	Perform diode test on U, V, W terminals.
Elevator Mechanics	Verify brake release and rail friction.
Parameters	Lengthen Accel/Decel times in Group C1.